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  • 151.
    Berglund, Martin
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Analyzing Edit Distance on Trees: Tree Swap Distance is Intractable2011In: Proceedings of the Prague Stringology Conference 2011 / [ed] Jan Holub and Jan Žďárek, Prague: Prague Stringology Club, Czech Technical University , 2011, p. 59-73Conference paper (Refereed)
    Abstract [en]

    The string correction problem looks at minimal ways to modify one stringinto another using fixed operations, such as for example inserting a symbol, deleting asymbol and interchanging the positions of two symbols (a “swap”). This has been generalizedto trees in various ways, but unfortunately having operations to insert/deletenodes in the tree and operations that move subtrees, such as a “swap” of adjacent subtrees,makes the correction problem for trees intractable. In this paper we investigatewhat happens when we have a tree edit distance problem with only swaps. We callthis problem tree swap distance, and go on to prove that this correction problem isNP-complete. This suggests that the swap operation is fundamentally problematic inthe tree case, and other subtree movement models should be studied.

  • 152.
    Berglund, Martin
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Drewes, Frank (Contributor)
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Characterizing Non-Regularity2014Report (Other academic)
    Abstract [en]

    This paper considers a characterization of the context-free non-regular languages, conjecturing that there for all such languages exists a fixed string thatcan be pumped to exhibit infinitely many equivalence classes. A proof is given only for a special case, but the general statement is conjectured to hold. The conjecture is then shown to imply that the shuffle of two context-free languagesis not context-free.

  • 153.
    Berglund, Martin
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Complexities of Order-Related Formal Language Extensions2014Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The work presented in this thesis discusses various formal language formalisms that extend classical formalisms like regular expressions and context-free grammars with additional abilities, most relating to order. This is done while focusing on the impact these extensions have on the efficiency of parsing the languages generated. That is, rather than taking a step up on the Chomsky hierarchy to the context-sensitive languages, which makes parsing very difficult, a smaller step is taken, adding some mechanisms which permit interesting spatial (in)dependencies to be modeled.

    The most immediate example is shuffle formalisms, where existing language formalisms are extended by introducing operators which generate arbitrary interleavings of argument languages. For example, introducing a shuffle operator to the regular expressions does not make it possible to recognize context-free languages like anbn, but it does capture some non-context-free languages like the language of all strings containing the same number of as, bs and cs. The impact these additions have on parsing has many facets. Other than shuffle operators we also consider formalisms enforcing repeating substrings, formalisms moving substrings around, and formalisms that restrict which substrings may be concatenated. The formalisms studied here all have a number of properties in common.

    1. They are closely related to existing regular and context-free formalisms. They operate in a step-wise fashion, deriving strings by sequences of rule applications of individually limited power.
    2. Each step generates a constant number of symbols and does not modify parts that have already been generated. That is, strings are built in an additive fashion that does not explode in size (in contrast to e.g. Lindenmayer systems). All languages here will have a semi-linear Parikh image.
    3. They feature some interesting characteristic involving order or other spatial constraints. In the example of the shuffle multiple derivations are in a sense interspersed in a way that each is unaware of.
    4. All of the formalisms are intended to be limited enough to make an efficient parsing algorithm at least for some cases a reasonable goal.

    This thesis will give intuitive explanations of a number of formalisms fulfilling these requirements, and will sketch some results relating to the parsing problem for them. This should all be viewed as preparation for the more complete results and explanations featured in the papers given in the appendices.

  • 154.
    Berglund, Martin
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Complexities of Parsing in the Presence of Reordering2012Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The work presented in this thesis discusses various formalisms for representing the addition of order-controlling and order-relaxing mechanisms to existing formal language models. An immediate example is shuffle expressions, which can represent not only all regular languages (a regular expression is a shuffle expression), but also features additional operations that generate arbitrary interleavings of its argument strings. This defines a language class which, on the one hand, does not contain all context-free languages, but, on the other hand contains an infinite number of languages that are not context-free. Shuffle expressions are, however, not themselves the main interest of this thesis. Instead we consider several formalisms that share many of their properties, where some are direct generalisations of shuffle expressions, while others feature very different methods of controlling order. Notably all formalisms that are studied here

    • have a semi-linear Parikh image,
    • are structured so that each derivation step generates at most a constant number of symbols (as opposed to the parallel derivations in for example Lindenmayer systems),
    • feature interesting ordering characteristics, created either by derivation steps that may generate symbols in multiple places at once, or by multiple generating processes that produce output independently in an interleaved fashion, and
    • are all limited enough to make the question of efficient parsing an interesting and reasonable goal.

    This vague description already hints towards the formalisms considered; the different classes of mildly context-sensitive devices and concurrent finite-state automata.

    This thesis will first explain and discuss these formalisms, and will then primarily focus on the associated membership problem (or parsing problem). Several parsing results are discussed here, and the papers in the appendix give a more complete picture of these problems and some related ones.

  • 155.
    Berglund, Martin
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    The Membership Problem for the Shuffle of Two Deterministic Linear Context-Free Languages is NP-complete2012Report (Other academic)
    Abstract [en]

    Formal language models which employ shuffling, or interleaving, of strings are of interest in many areas of computer science. Notable examples include system verification, plan recognition, and natural language processing. Membership problems for the shuffle of languages are especially interesting. It is known that deciding membership for shuffles of regular languages can be done in polynomial time, and that deciding (non-uniform) membership in the shuffle of two deterministic context-free languages is NP-complete. In this paper we narrow the gap by showing that the non-uniform membership problem for the shuffle of two deterministic *linear* context-free languages is NP-complete.

  • 156.
    Berglund, Martin
    et al.
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Björklund, Henrik
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Björklund, Johanna
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Shuffled languages: representation and recognition2013In: Theoretical Computer Science, ISSN 0304-3975, E-ISSN 1879-2294, Vol. 489-490, p. 1-20Article in journal (Refereed)
    Abstract [en]

    Language models that use interleaving, or shuffle, operators have applications in various areas of computer science, including system verification, plan recognition, and natural language processing. We study the complexity of the membership problem for such models, in other words, how difficult it is to determine if a string belongs to a language or not. In particular, we investigate how interleaving can be introduced into models that capture the context-free languages.

  • 157.
    Berglund, Martin
    et al.
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Björklund, Henrik
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Drewes, Frank
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    On the Parameterized Complexity of Linear Context-Free Rewriting Systems2013In: Proceedings of the 13th Meeting on the Mathematics of Language (MoL 13), Association for Computational Linguistics, 2013, p. 21-29Conference paper (Other academic)
    Abstract [en]

    We study the complexity of uniform membership for Linear Context-Free RewritingSystems, i.e., the problem where we aregiven a string w and a grammar G and areasked whether w ∈ L(G). In particular,we use parameterized complexity theoryto investigate how the complexity dependson various parameters. While we focusprimarily on rank and fan-out, derivationlength is also considered.

  • 158.
    Berglund, Martin
    et al.
    Stellenbosch University.
    Björklund, Henrik
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Drewes, Frank
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Single-Rooted DAGs in Regular DAG Languages: Parikh Image and Path Languages2017In: Proceedings of the 13th International Workshop on Tree Adjoining Grammars and Related Formalisms (TAG+13) / [ed] M. Kuhlmann, T. Scheffler, Association for Computational Linguistics , 2017, p. 94-101Conference paper (Refereed)
    Abstract [en]

    In a recent survey (Drewes, 2017) of results on DAG automata  some open problems are formulated for the case where the  DAG language accepted by a DAG automaton A is restricted to DAGs with a single root, denoted by L(A)u. Here we consider each of  those problems, demonstrating that: (i) the finiteness  of L(A)u is decidable, (ii) the path languages of L(A)u can be characterized in  terms of the string languages accepted by partially blind  multicounter automata, and  (iii) the Parikh image of L(A)u is semilinear.

  • 159.
    Berglund, Martin
    et al.
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Björklund, Henrik
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Drewes, Frank
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    van der Merwe, Brink
    Stellenbosch University, South Africa.
    Watson, Bruce
    Stellenbosch University, South Africa.
    Cuts in Regular Expressions2013In: Developments in Language Theory: 17th International Conference, DLT 2013, Marne-la-Vallée, France, June 18-21, 2013. Proceedings / [ed] Marie-Pierre Béal, Olivier Carton, Springer Berlin/Heidelberg, 2013, p. 70-81Conference paper (Refereed)
    Abstract [en]

    Most software packages with regular expression matching engines offer operators that extend the classical regular expressions, such as counting, intersection, complementation, and interleaving. Some of the most popular engines, for example those of Java and Perl, also provide operators that are intended to control the nondeterminism inherent in regular expressions. We formalize this notion in the form of the cut and iterated cut operators. They do not extend the class of languages that can be defined beyond the regular, but they allow for exponentially more succinct representation of some languages. Membership testing remains polynomial, but emptiness testing becomes PSPACE-hard. 

  • 160.
    Berglund, Martin
    et al.
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Björklund, Henrik
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Högberg, Johanna
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Recognizing shuffled languages2011In: Language and Automata Theory and Applications: 5th International Conference, LATA 2011, Tarragona, Spain, May 26-31, 2011. Proceedings / [ed] Adrian-Horia Dediu, Shunsuke Inenaga and Carlos Martín-Vide, Springer Berlin/Heidelberg, 2011, p. 142-154Conference paper (Refereed)
    Abstract [en]

    Language models that use interleaving, or shuffle, operators have applications in various areas of computer science, including system verification, plan recognition, and natural language processing. We study the complexity of the membership problem for such models, i.e., how difficult it is to determine if a string belongs to a language or not. In particular, we investigate how interleaving can be introduced into models that capture the context-free languages.

  • 161.
    Berglund, Martin
    et al.
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Björklund, Henrik
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Högberg, Johanna
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Recognizing Shuffled Languages2011Report (Other academic)
    Abstract [en]

    Language models that use interleaving, or shuffle, operators have applications in various areas of computer science, including system verification, plan recognition, and natural language processing. We study the complexity of the membership problem for such models, i.e., how difficult it is to determine if a string belongs to a language or not. In particular, we investigate how interleaving can be introduced into models that capture the context-free languages.

  • 162.
    Berglund, Martin
    et al.
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Drewes, Frank
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    On the complexity of variants of the k Best strings problem2010In: Proceedings of the Prague stringology conference 2010, dblp , 2010, p. 76-88Conference paper (Refereed)
    Abstract [en]

    We investigate the problem of extracting the k best strings from a nondeterministic weighted automaton over a semiring S. This problem, which has been considered earlier in the literature, is more difficult than extracting the k best runs, since distinct runs may not correspond to distinct strings. Unsurprisingly, the computational complexity of the problem depends on the semiring S used. We study three different cases, namely the tropical and complex tropical semirings, and the semiring of positive real numbers. For the first case, we establish a polynomial algorithm. For the second and third cases, NP-completeness and undecidability results are shown.

  • 163.
    Berglund, Martin
    et al.
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Drewes, Frank
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    On the complexity of variants of the k best strings problem2010In: Proc. Prague Stringology Conference 2010 / [ed] M. Balík, J. Holub, 2010Conference paper (Refereed)
  • 164.
    Berglund, Martin
    et al.
    Stellenbosch University.
    Drewes, Frank
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Merwe, Brink van der
    University of Stellenbosch.
    On Regular Expressions with Backreferences and Transducers2018In: Tenth Workshop on Non-Classical Models of Automata and Applications (NCMA 2018) / [ed] Rudolf Freund, Michal Hospodár, Galina Jirásková, Giovanni Pighizzini, Österreichische Computer Gesellschaft , 2018, p. 49-64Conference paper (Refereed)
    Abstract [en]

    Modern regular expression matching software features many extensions, some general, while some are very narrowly specified. Here we consider the generalization of adding a class of operators which can be described by, e.g. finite-state transducers. Combined with backreferences, they enable new classes of languages to be matched. The addition of finite-state transducers is shown to make membership testing undecidable. Following this result, we study the complexity of membership testing for various restricted cases of the model.

  • 165.
    Berglund, Martin
    et al.
    Stellenbosch University.
    Drewes, Frank
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Merwe, Brink van der
    University of Stellenbosch.
    The output size problem for string-to-tree transducers2018In: Journal of Automata, Languages and Combinatorics, Vol. 23, no 1-3, p. 19-38Article in journal (Refereed)
    Abstract [en]

    The output size problem, for a string-to-tree transducer, is to determine the asymptotic behavior of the function describing the maximum size of output trees, with respect to the length of input strings. We show that the problem to determine, for a given regular expression, the worst-case matching time of a backtracking regular expression matcher, can be reduced to the output size problem. The latter can, in turn, be solved by determining the degree of ambiguity of a non-deterministic finite automaton.

  • 166.
    Berglund, Martin
    et al.
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Drewes, Frank
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    van der Merwe, Brink
    University of Stellenbosch, South Africa.
    Analyzing Catastrophic Backtracking Behavior in Practical Regular Expression Matching2014Conference paper (Refereed)
    Abstract [en]

    We consider in some detail how regular expression matching happens in Java, as a popular representative of the category of regex-directed matching engines. We extract a slightly idealized algorithm for this scenario. Next we define an automata model which captures all the aspects needed to perform matching, of the Java style, in a formal way. Finally, two types of static analysis, which take a regular expression and tells whether there exists a family of strings which make Java-style matching run in exponential time, are done.

  • 167.
    Berglund, Martin
    et al.
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    van der Merwe, Brink
    On the semantics of regular expression parsing in the wild2017In: Theoretical Computer Science, ISSN 0304-3975, E-ISSN 1879-2294, Vol. 679, p. 69-82Article in journal (Refereed)
    Abstract [en]

    We introduce prioritized transducers to formalize capturing groups in regular expression matching in a way that permits straightforward modeling of capturing in Java's 1 regular expression library. The broader questions of parsing semantics and performance are also considered. In addition, the complexity of deciding equivalence of regular expressions with capturing groups is investigated.

  • 168.
    Bergman, Åsa
    et al.
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Lövström, Cecilia
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Usability Improvement and Re-Design of SIMAIR - an Air Quality Assessment Tool2012Independent thesis Advanced level (degree of Master (One Year)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The thesis propose a new design solution of the web application and air assessment tool: SIMAIR, a product of The Swedish Meteorological and Hydrological Institute (SMHI). The current solution of SIMAIR is outdated regarding the interaction and visual apperance, as a result it is in need of a user adaption. No user study has been perform earlier and for that reason SMHI needs an increased knowledge about the users. The objectives of this thesis are therefore to perform a user study, develop a more user-friendly design and implementan interactive prototype of the new design solution.

    By using the design method Goal-Directed Design, a design target of the wide spread user group was found and personas of the user archetypes were developed. By narrowing down the target audience, the new design was more well defined and the chances to create a product that satisfied the users' needs increased.

    The design target and the personas was used to find goals and motivations, as well as aptitudes and attitudes, of the users. "Seriousness", "Professionalism" and "Reliability" were the objectives for the new design. They formed the basis for the creation and development of a modernized and user-friendly graphical user interface of SIMAIR. The prototypeto visualize the new interface, was developed by using HTML5, CSS3 and the JavaScript libraryJQuery. These technologies are also, well suited for further development and usability improvement of SIMAIR.

  • 169.
    Bergström, Lars
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Syntaxbaserad författarigenkänning2010Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    The writing style of a particular author can be divided into many subfeatures, for example use of words, language and syntax. Focusing on the latter, this study aims to show how well syntactic information alone can attribute the correct author to a document. Syntactic information is defined as overlapping syntactic subtrees of height one (1) for all sentences of all included documents. The performance is compared to that of the previously very successful method of comparing stop word frequencies. These are words normally excluded from search engine queries, because they are present in all sorts of texts regardless of topic. However, this property is a positive feature when it comes to authorship attribution, as it allows for context-free comparisons of texts. Training and test data is obtained from the icwsm 2009 corpus, containing some 200 igabyte of blog posts and news articles. This data is automatically filtered to create a reasonably large collection (about 250000 documents) while remaining manageable by an automatic natural language parser (Stanford nlp) within the constraints of time. The filtering process guarantees that all texts used for comparison has texts of the same author within the training portion of the data. Indexing and searching is done using Latent Semantic Indexing (lsi). All documents are represented by a vector in multidimensional space, thus creating a matrix of document vectors. Search documents are then matched with those in the matrix by calculating the angles between document vectors, returning those with the smallest angular difference to the query document. The process of creating a document matrix and search documents is repeated multiple times, creating a new document matrix of randomly selected authors  every time. The performance of the different methods are measured by comparing average scores for each created document matrix. The results show that by average the syntactic information is more successful in correct authorship recognition compared to both chance and stop word frequency analysis. These results hold true for all tested numbers of authors present within the index matrix, ranging from ten to one hundred unique authors.

  • 170.
    Bergström, Mattias
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Designing Touch Interaction for a 3D Game2015Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The marketshare of touch devices is increasing, and so is the number of games on that platform. As touch devices have become almost as powerful as game consoles, games from the PC and console platforms are being adapted to these touch devices. Console and PC games often feature quite complex controls which can be difficult to implement on touch devices.

    This thesis details the design, implementation, and evaluation of methods of interacting with a 3D game on touch devices. The project was performed at Dohi Sweden on the game MilMo, which is a 3D game currently available on the web.

    The results of this projects was two prototypes that were evaluated using both user tests as well as heuristic evaluation. The evaluation show that one of the prototypes was preferred because it was more similar to other existing solutions.

  • 171.
    Bernland, Anders
    et al.
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Wadbro, Eddie
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Berggren, Martin
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Acoustic shape optimization using cut finite elements2018In: International Journal for Numerical Methods in Engineering, ISSN 0029-5981, E-ISSN 1097-0207, Vol. 113, no 3, p. 432-449Article in journal (Refereed)
    Abstract [en]

    Fictitious domain methods are attractive for shape optimization applications, since they do not require deformed or regenerated meshes. A recently developed such method is the CutFEM approach, which allows crisp boundary representations and for which uniformly well-conditioned system matrices can be guaranteed. Here, we investigate the use of the CutFEM approach for acoustic shape optimization, using as test problem the design of an acoustic horn for favorable impedance-matching properties. The CutFEM approach is used to solve the Helmholtz equation, and the geometry of the horn is implicitly described by a level-set function. To promote smooth algorithmic updates of the geometry, we propose to use the nodal values of the Laplacian of the level-set function as design variables. This strategy also improves the algorithm's convergence rate, counteracts mesh dependence, and, in combination with Tikhonov regularization, controls small details in the optimized designs. An advantage with the proposed method is that the exact derivatives of the discrete objective function can be expressed as boundary integrals, as opposed to when using a traditional method that uses mesh deformations. The resulting horns possess excellent impedance-matching properties and exhibit surprising subwavelength structures, not previously seen, which are possible to capture due to the fixed mesh approach.

  • 172.
    Bernland, Anders
    et al.
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Wadbro, Eddie
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Berggren, Martin
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    SHAPE OPTIMIZATION OF A COMPRESSION DRIVER PHASE PLUG2019In: SIAM Journal on Scientific Computing, ISSN 1064-8275, E-ISSN 1095-7197, Vol. 41, no 1, p. B181-B204Article in journal (Refereed)
    Abstract [en]

    A compression driver is an electro-acoustic transducer with considerably higher efficiency than direct radiating loudspeakers, thanks to the increased radiation resistance caused by a large vibrating diaphragm placed in a compression chamber with small openings. The transition section between compression chamber and output waveguide, the phase plug, must be carefully designed to avoid irregularities in the output sound pressure level (SPL) as a function of frequency. Here we present a shape optimization method based on an implicit level-set description and adjoint sensitivity analysis, which enables a large number of design parameters and vast design freedom. The CutFEM approach, a fictitious domain finite element method, removes the need for mesh updates and makes the method robust and computationally inexpensive. Numerical experiments for a generic annular diaphragm compression driver are presented, with optimized designs showing only minor frequency irregularities. Two different objective functions are considered: one for maximum SPL and one where the SPL is fitted to that of a hypothetical ideal design; the latter approach is found to be more effective in reducing irregularities. Visco-thermal boundary-layer losses are included in a post-processing step, and, though the influence of losses is clearly noticeable, the overall performance is similar and the optimized designs still outperform the original design.

  • 173.
    Bhuyan, Monowar H.
    et al.
    Umeå University, Faculty of Science and Technology, Department of Computing Science. Umea University.
    Elmroth, Erik
    Umeå University, Faculty of Science and Technology, Department of Computing Science. Umea University.
    Multi-Scale Low-Rate DDoS Attack Detection Using the Generalized Total Variation Metric2018In: 17th IEEE International Conference on Machine Learning and Applications, IEEE, 2018, p. 1040-1047Conference paper (Refereed)
    Abstract [en]

    We propose a mechanism to detect multi-scale low-rate DDoS attacks which uses a generalized total variation metric. The proposed metric is highly sensitive towards detecting different variations in the network traffic and evoke more distance between legitimate and attack traffic as compared to the other detection mechanisms. Most low-rate attackers invade the security system by scale-in-and-out of periodic packet burst towards the bottleneck router which severely degrades the Quality of Service (QoS) of TCP applications. Our proposed mechanism can effectively identify attack traffic of this natures, despite its similarity to legitimate traffic, based on the spacing value of our metric. We evaluated our mechanism using datasets from CAIDA DDoS, MIT Lincoln Lab, and real-time testbed traffic. Our results demonstrate that our mechanism exhibits good accuracy and scalability in the detection of multi-scale low-rate DDoS attacks.

  • 174.
    Bilander, Jesper
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Transferring heterogeneous data from generic databases into a SQL database using HTTPPossibilities and Implementation2017Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The thesis investigates the possibility to create software that can synchronize heterogeneous data from generic databases through the Internet. To further enhance the conclusion, we implement a prototype that fetches data from numerous source system databases, and stores the data in another location, more accessible for processing. To achieve that, previous work with topics related to the area was inspected and analyzed. Based on the investigation, the implemented prototype uses a client-server approach which communicates with a REST-like design using JSON-strings and HTTP. This thesis and the resulting prototype proves that it is fully possible to create such software by combining and using existing protocols and frameworks.i

  • 175.
    Billing, Erik
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Cognition Rehearsed: Recognition and Reproduction of Demonstrated Behavior2012Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The work presented in this dissertation investigates techniques for robot Learning from Demonstration (LFD). LFD is a well established approach where the robot is to learn from a set of demonstrations. The dissertation focuses on LFD where a human teacher demonstrates a behavior by controlling the robot via teleoperation. After demonstration, the robot should be able to reproduce the demonstrated behavior under varying conditions. In particular, the dissertation investigates techniques where previous behavioral knowledge is used as bias for generalization of demonstrations.

    The primary contribution of this work is the development and evaluation of a semi-reactive approach to LFD called Predictive Sequence Learning (PSL). PSL has many interesting properties applied as a learning algorithm for robots. Few assumptions are introduced and little task-specific configuration is needed. PSL can be seen as a variable-order Markov model that progressively builds up the ability to predict or simulate future sensory-motor events, given a history of past events. The knowledge base generated during learning can be used to control the robot, such that the demonstrated behavior is reproduced. The same knowledge base can also be used to recognize an on-going behavior by comparing predicted sensor states with actual observations. Behavior recognition is an important part of LFD, both as a way to communicate with the human user and as a technique that allows the robot to use previous knowledge as parts of new, more complex, controllers.

    In addition to the work on PSL, this dissertation provides a broad discussion on representation, recognition, and learning of robot behavior. LFD-related concepts such as demonstration, repetition, goal, and behavior are defined and analyzed, with focus on how bias is introduced by the use of behavior primitives. This analysis results in a formalism where LFD is described as transitions between information spaces. Assuming that the behavior recognition problem is partly solved, ways to deal with remaining ambiguities in the interpretation of a demonstration are proposed.

    The evaluation of PSL shows that the algorithm can efficiently learn and reproduce simple behaviors. The algorithm is able to generalize to previously unseen situations while maintaining the reactive properties of the system. As the complexity of the demonstrated behavior increases, knowledge of one part of the behavior sometimes interferes with knowledge of another parts. As a result, different situations with similar sensory-motor interactions are sometimes confused and the robot fails to reproduce the behavior.

    One way to handle these issues is to introduce a context layer that can support PSL by providing bias for predictions. Parts of the knowledge base that appear to fit the present context are highlighted, while other parts are inhibited. Which context should be active is continually re-evaluated using behavior recognition. This technique takes inspiration from several neurocomputational models that describe parts of the human brain as a hierarchical prediction system. With behavior recognition active, continually selecting the most suitable context for the present situation, the problem of knowledge interference is significantly reduced and the robot can successfully reproduce also more complex behaviors.

  • 176.
    Billing, Erik
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Cognition reversed: Robot learning from demonstration2009Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The work presented in this thesis investigates techniques for learning from demonstration (LFD). LFD is a well established approach to robot learning, where a teacher demonstrates a behavior to a robot pupil. This thesis focuses on LFD where a human teacher demonstrates a behavior by controlling the robot via teleoperation. The robot should after demonstration be able to execute the demonstrated behavior under varying conditions.

    Several views on representation, recognition and learning of robot behavior are presented and discussed from a cognitive and computational perspective. LFD-related concepts such as behavior, goal, demonstration, and repetition are defined and analyzed, with focus on how bias is introduced by the use of behavior primitives. This analysis results in a formalism where LFD is described as transitions between information spaces. Assuming that the behavior recognition problem is partly solved, ways to deal with remaining ambiguities in the interpretation of a demonstration are proposed.

    A total of five algorithms for behavior recognition are proposed and evaluated, including the dynamic temporal difference algorithm Predictive Sequence Learning (PSL). PSL is model-free in the sense that it makes few assumptions of what is to be learned. One strength of PSL is that it can be used for both robot control and recognition of behavior. While many methods for behavior recognition are concerned with identifying invariants within a set of demonstrations, PSL takes a different approach by using purely predictive measures. This may be one way to reduce the need for bias in learning. PSL is, in its current form, subjected to combinatorial explosion as the input space grows, which makes it necessary to introduce some higher level coordination for learning of complex behaviors in real-world robots.

    The thesis also gives a broad introduction to computational models of the human brain, where a tight coupling between perception and action plays a central role. With the focus on generation of bias, typical features of existing attempts to explain humans' and other animals' ability to learn are presented and analyzed, from both a neurological and an information theoretic perspective. Based on this analysis, four requirements for implementing general learning ability in robots are proposed. These requirements provide guidance to how a coordinating structure around PSL and similar algorithms should be implemented in a model-free way.

  • 177.
    Billing, Erik
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Cognitive Perspectives on Robot Behavior2010In: Proceedings of the 2nd International Conference on Agents and Artificial Intelligence: Special Session on Computing Languages with Multi-Agent Systems and Bio-Inspired Devices / [ed] Joaquim Filipe, Ana Fred and Bernadette Sharp, Portugal: INSTICC , 2010, p. 373-382Conference paper (Refereed)
    Abstract [en]

    A growing body of research within the field of intelligent robotics argues for a view of intelligence drastically different from classical artificial intelligence and cognitive science. The holistic and embodied ideas expressed by this research promote the view that intelligence is an emergent phenomenon. Similar perspectives, where numerous interactions within the system lead to emergent properties and cognitive abilities beyond that of the individual parts, can be found within many scientific fields. With the goal of understanding how behavior may be represented in robots, the present review tries to grasp what this notion of emergence really means and compare it with a selection of theories developed for analysis of human cognition, including the extended mind, distributed cognition and situated action. These theories reveal a view of intelligence where common notions of objects, goals, language and reasoning have to be rethought. A view where behavior, as well as the agent as such, is defined by the observer rather than given by their nature. Structures in the environment emerge by interaction rather than recognized. In such a view, the fundamental question is how emergent systems appear and develop, and how they may be controlled.

  • 178.
    Billing, Erik
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Representing behavior: Distributed theories in a context of robotics2007Report (Other academic)
    Abstract [en]

    A growing body of research within the field of intelligent robotics argues for a view of intelligence drastically different from classical artificial intelligence and cognitive science. The holistic and embodied ideas expressed by this research sees emergence as the springing source for intelligence. Similar perspectives, where numerous interactions within the system lead to emergent properties and cognitive abilities beyond that of the individual parts, can be found within many scientific fields. With the goal of understanding how behavior may be represented in robots, the present review tries to grasp what this notion of emergence really means and compare it with a selection of theories developed for analysis of human cognition. These theories reveal a view of intelligence where common notions of objects, goals and reasoning have to be rethought. A view where behavior, as well as the agent as such, is in the eye of the observer rather than given. Structures in the environment is achieved by interaction rather than recognized. In such a view, the fundamental question is how emergent systems appear and develop, and how they may be controlled.

  • 179.
    Billing, Erik
    et al.
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Hellström, Thomas
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    A formalism for learning from demonstration2010In: Paladyn Journal of Behavioral Robotics, ISSN 2080-9778, 2081-4836 (e-version), Vol. 1, no 1, p. 1-13Article in journal (Refereed)
    Abstract [en]

    The paper describes and formalizes the concepts and assumptions involved in Learning from Demonstration (LFD), a common learning technique used in robotics. LFD-related concepts like goal, generalization, and repetition are here defined, analyzed, and put into context. Robot behaviors are described in terms of trajectories through information spaces and learning is formulated as mappings between some of these spaces. Finally, behavior primitives are introduced as one example of good bias in learning, dividing the learning process into the three stages of behavior segmentation, behavior recognition, and behavior coordination. The formalism is exemplified through a sequence learning task where a robot equipped with a gripper arm is to move objects to specific areas. The introduced concepts are illustrated with special focus on how bias of various kinds can be used to enable learning from a single demonstration, and how ambiguities in demonstrations can be identified and handled.

  • 180.
    Billing, Erik
    et al.
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Hellström, Thomas
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Behavior recognition for segmentation of demonstrated tasks2008In: IEEE SMC International Conference on Distributed Human-Machine Systems (DHMS), 2008Conference paper (Refereed)
    Abstract [en]

    One common approach to the robot learning technique Learning From Demonstration, is to use a set of pre-programmed skills as building blocks for more complex tasks. One important part of this approach is recognition of these skills in a demonstration comprising a stream of sensor and actuator data. In this paper, three novel techniques for behavior recognition are presented and compared. The first technique is function-oriented and compares actions for similar inputs. The second technique is based on auto-associative neural networks and compares reconstruction errors in sensory-motor space. The third technique is based on S-Learning and compares sequences of patterns in sensory-motor space. All three techniques compute an activity level which can be seen as an alternative to a pure classification approach. Performed tests show how the former approach allows a more informative interpretation of a demonstration, by not determining "correct" behaviors but rather a number of alternative interpretations.

  • 181.
    Billing, Erik
    et al.
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Hellström, Thomas
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Formalising learning from demonstration2008Report (Other academic)
    Abstract [en]

    The paper describes and formalizes the concepts and assumptions involved in Learning from Demonstration (LFD), a common learning technique used in robotics. Inspired by the work on planning and actuation by LaValle, common LFD-related concepts like goal, generalization, and repetition are here defined, analyzed, and put into context. Robot behaviors are described in terms of trajectories through information spaces and learning is formulated as the mappings between some of these spaces. Finally, behavior primitives are introduced as one example of useful bias in the learning process, dividing the learning process into the three stages of behavior segmentation, behavior recognition, and behavior coordination.

  • 182.
    Billing, Erik
    et al.
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Hellström, Thomas
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Predictive Learning in Context2010In: Proceedings of the tenth international conference on epigenetic robotics: modeling cognitive development in robotic systems / [ed] Birger Johansson, Erol Sahin & Christian Balkenius, Lund, Sweden, 2010, p. 157-158Conference paper (Refereed)
  • 183.
    Billing, Erik
    et al.
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Hellström, Thomas
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Predictive learning in context2010In: Proceedings of the 10th International Conference on Epigenetic Robotics: Modelling Cognitive Development in Robotic Systems, Lund University , 2010, p. 157-158Conference paper (Refereed)
  • 184.
    Billing, Erik
    et al.
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Hellström, Thomas
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Janlert, Lars Erik
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Behavior recognition for learning from demonstration2010In: Proceedings of IEEE International Conference on Robotics and Automation / [ed] Nancy M. Amato et. al, 2010, p. 866-872Conference paper (Refereed)
    Abstract [en]

    Two methods for behavior recognition are presented and evaluated. Both methods are based on the dynamic temporal difference algorithm Predictive Sequence Learning (PSL) which has previously been proposed as a learning algorithm for robot control. One strength of the proposed recognition methods is that the model PSL builds to recognize behaviors is identical to that used for control, implying that the controller (inverse model) and the recognition algorithm (forward model) can be implemented as two aspects of the same model. The two proposed methods, PSLE-Comparison and PSLH-Comparison, are evaluated in a Learning from Demonstration setting, where each algorithm should recognize a known skill in a demonstration performed via teleoperation. PSLH-Comparison produced the smallest recognition error. The results indicate that PSLH-Comparison could be a suitable algorithm for integration in a hierarchical control system consistent with recent models of human perception and motor control.

  • 185.
    Billing, Erik
    et al.
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Hellström, Thomas
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Janlert, Lars Erik
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Model-free learning from demonstration2010In: ICAART 2010 - Proceedings of the international conference on agents and artificial intelligence:  volume 2 / [ed] Joaquim Filipe, Ana LN Fred, Bernadette Sharp, Portugal: INSTICC , 2010, p. 62-71Conference paper (Refereed)
    Abstract [en]

    A novel robot learning algorithm called Predictive Sequence Learning (PSL) is presented and evaluated. PSL is a model-free prediction algorithm inspired by the dynamic temporal difference algorithm S-Learning. While S-Learning has previously been applied as a reinforcement learning algorithm for robots, PSL is here applied to a Learning from Demonstration problem. The proposed algorithm is evaluated on four tasks using a Khepera II robot. PSL builds a model from demonstrated data which is used to repeat the demonstrated behavior. After training, PSL can control the robot by continually predicting the next action, based on the sequence of passed sensor and motor events. PSL was able to successfully learn and repeat the first three (elementary) tasks, but it was unable to successfully repeat the fourth (composed) behavior. The results indicate that PSL is suitable for learning problems up to a certain complexity, while higher level coordination is required for learning more complex behaviors.

  • 186.
    Billing, Erik
    et al.
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Hellström, Thomas
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Janlert, Lars Erik
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Predictive learning from demonstration2011In: Agents and artificial Intelligence: Second International Conference, ICAART 2010, Valencia, Spain, January 22-24, 2010. Revised Selected Papers / [ed] Filipe, Joaquim, Fred, Ana, Sharp, Bernadette, Berlin: Springer Verlag , 2011, 1, p. 186-200Chapter in book (Refereed)
    Abstract [en]

    A model-free learning algorithm called Predictive Sequence Learning (PSL) is presented and evaluated in a robot Learning from Demonstration (LFD) setting. PSL is inspired by several functional models of the brain. It constructs sequences of predictable sensory-motor patterns, without relying on predefined higher-level concepts. The algorithm is demonstrated on a Khepera II robot in four different tasks. During training, PSL generates a hypothesis library from demonstrated data. The library is then used to control the robot by continually predicting the next action, based on the sequence of passed sensor and motor events. In this way, the robot reproduces the demonstrated behavior. PSL is able to successfully learn and repeat three elementary tasks, but is unable to repeat a fourth, composed behavior. The results indicate that PSL is suitable for learning problems up to a certain complexity, while higher level coordination is required for learning more complex behaviors.

  • 187.
    Billing, Erik
    et al.
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Hellström, Thomas
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Janlert, Lars Erik
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Robot learning from demonstration using predictive sequence learning2011In: Robotic systems: applications, control and programming / [ed] Ashish Dutta, Kanpur, India: IN-TECH, 2011, p. 235-250Chapter in book (Refereed)
    Abstract [en]

    In this chapter, the prediction algorithm Predictive Sequence Learning (PSL) is presented and evaluated in a robot Learning from Demonstration (LFD) setting. PSL generates hypotheses from a sequence of sensory-motor events. Generated hypotheses can be used as a semi-reactive controller for robots. PSL has previously been used as a method for LFD, but suffered from combinatorial explosion when applied to data with many dimensions, such as high dimensional sensor and motor data. A new version of PSL, referred to as Fuzzy Predictive Sequence Learning (FPSL), is presented and evaluated in this chapter. FPSL is implemented as a Fuzzy Logic rule base and works on a continuous state space, in contrast to the discrete state space used in the original design of PSL. The evaluation of FPSL shows a significant performance improvement in comparison to the discrete version of the algorithm. Applied to an LFD task in a simulated apartment environment, the robot is able to learn to navigate to a specific location, starting from an unknown position in the apartment.

  • 188.
    Billing, Erik
    et al.
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Hellström, Thomas
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Janlert, Lars Erik
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Simultaneous control and recognition of demonstrated behavior2011Report (Other academic)
    Abstract [en]

    A method for Learning from Demonstration (LFD) is presented and evaluated on a simulated Robosoft Kompai robot. The presented algorithm, called Predictive Sequence Learning (PSL), builds fuzzy rules describing temporal relations between sensory-motor events recorded while a human operator is tele-operating the robot. The generated rule base can be used to control the robot and to predict expected sensor events in response to executed actions. The rule base can be trained under different contexts, represented as fuzzy sets. In the present work, contexts are used to represent different behaviors. Several behaviors can in this way be stored in the same rule base and partly share information. The context that best matches present circumstances can be identified using the predictive model and the robot can in this way automatically identify the most suitable behavior for precent circumstances. The performance of PSL as a method for LFD is evaluated with, and without, contextual information. The results indicate that PSL without contexts can learn and reproduce simple behaviors. The system also successfully identifies the most suitable context in almost all test cases. The robot's ability to reproduce more complex behaviors, with partly overlapping and conflicting information, significantly increases with the use of contexts. The results support a further development of PSL as a component of a dynamic hierarchical system performing control and predictions on several levels of abstraction. 

  • 189. Billing, Erik
    et al.
    Hellström, Thomas
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Janlert, Lars-Erik
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Simultaneous recognition and reproduction of demonstrated behavior2015In: Biologically Inspired Cognitive Architectures, ISSN 2212-683X, Vol. 12, p. 43-53Article in journal (Refereed)
    Abstract [en]

    Predictions of sensory-motor interactions with the world is often referred to as a key component in cognition. We here demonstrate that prediction of sensory-motor events, i.e., relationships between percepts and actions, is sufficient to learn navigation skills for a robot navigating in an apartment environment. In the evaluated application, the simulated Robosoft Kompai robot learns from human demonstrations. The system builds fuzzy rules describing temporal relations between sensory-motor events recorded while a human operator is tele-operating the robot. With this architecture, referred to as Predictive Sequence Learning (PSL), learned associations can be used to control the robot and to predict expected sensor events in response to executed actions. The predictive component of PSL is used in two ways: (1) to identify which behavior that best matches current context and (2) to decide when to learn, i.e., update the confidence of different sensory-motor associations. Using this approach, knowledge interference due to over-fitting of an increasingly complex world model can be avoided. The system can also automatically estimate the confidence in the currently executed behavior and decide when to switch to an alternate behavior. The performance of PSL as a method for learning from demonstration is evaluated with, and without, contextual information. The results indicate that PSL without contextual information can learn and reproduce simple behaviors, but fails when the behavioral repertoire becomes more diverse. When a contextual layer is added, PSL successfully identifies the most suitable behavior in almost all test cases. The robot's ability to reproduce more complex behaviors, with partly overlapping and conflicting information, significantly increases with the use of contextual information. The results support a further development of PSL as a component of a dynamic hierarchical system performing control and predictions on several levels of abstraction.

  • 190.
    Billing, Erik
    et al.
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Servin, Martin
    Umeå University, Faculty of Science and Technology, Department of Physics.
    Composer: A prototype multilingual model composition tool2013In: MODPROD2013: 7th MODPROD Workshop on Model-Based Product Development / [ed] Peter Fritzson, Umeå: Umeå universitet , 2013Conference paper (Other academic)
    Abstract [en]

    Composer - A prototype multilingual model composition tool

    Erik Billing and Martin Servin

    November 10, 2012

    Facing the task to design, simulate or optimize a complex system itis common to find models and data for the system expressed in differentformats, implemented in different simulation software tools. When a newmodel is developed, a target platform is chosen and existing componentsimplemented with different tools have to be converted. This results inunnecessary work duplication and lead times. The Modelica languageinitiative [2] partially solves this by allowing developers to move modelsbetween different tools following the Modelica standard. Another possi-bility is to exchange models using the Functional Mockup Interface (FMI)standard that allows computer models to be used as components in othersimulations, possibly implemented using other programming languages[1]. With the Modelica and FMI standards entering development, there isneed for an easy-to-use tool that supports design, editing and simulationof such multilingual systems, as well as for retracting system informationfor formulating and solving optimization problems.A prototype solution for a graphical block diagram tool for design, edit-ing, simulation and optimization of multilingual systems has been createdand evaluated for a specific system. The tool is named Composer [3].The block diagram representation should be generic, independent ofmodel implementations, have a standardized format and yet support effi-cient handling of complex data. It is natural to look for solutions amongmodern web technologies, specifically HTML5. The format for represent-ing two dimensional vector graphics in HTML5 is Scalable Vector Graphics(SVG). We combine the SVG format with the FMI standard. In a firststage, we take the XML-based model description of FMI as a form for de-scribing the interface for each component, in a language independent way.Simulation parameters can also be expressed on this form, and integratedas metadata into the SVG image. 

    The prototype, using SVG in conjunction with FMI, is implementedin JavaScript and allow creation and modification of block diagrams directly in the web browser. Generated SVG images are sent to the serverwhere they are translated to program code, allowing the simulation ofthe dynamical system to be executed using selected implementations. Analternative mode is to generate optimization problem from the systemdefinition and model parameters. The simulation/optimization result is 

    returned to the web browser where it is plotted or processed using otherstandard libraries.The fiber production process at SCA Packaging Obbola [4] is used asan example system and modeled using Composer. The system consists oftwo fiber production lines that produce fiber going to a storage tank [5].The paper machine is taking fiber from the tank as needed for production.A lot of power is required during fiber production and the purpose of themodel was to investigate weather electricity costs could be reduced byrescheduling fiber production over the day, in accordance with the electricity spot price. Components are implemented for dynamical simulationusing OpenModelica and for discrete event using Python. The Python implementation supports constraint propagation between components andoptimization over specified variables. Each component is interfaced as aFunctional Mock-up Unit (FMU), allowing components to be connectedand properties specified in language independent way. From the SVGcontaining the high-level system information, both Modelica and Pythoncode is generated and executed on the web server, potentially hosted ina high performance data center. More implementations could be addedwithout modifying the SVG system description.We have shown that it is possible to separate system descriptions onthe block diagram level from implementations and interface between thetwo levels using FMI. In a continuation of this project, we aim to integratethe FMI standard also for co-simulation, such that components implemented in different languages could be used together. One open questionis to what extent FMUs of the same component, but implemented withdifferent tools, will have the same model description. For the SVG-basedsystem description to be useful, the FMI model description must remainthe same, or at least contain a large overlap, for a single component implemented in different languages. This will be further investigated in futurework.

    References

    [1] Modelica Association. Functional mock-up interface, http://www.fmi-standard.org, November 2012.

    [2] Modelica Association. Modelica and the modelica association, http://www.modelica.org, November 2012.

    [3] Erik Billing and Martin Servin. Composer, http://imuit.cs.umu.se/composer, November 2012. [4] SCA Packaging. Sca packaging obbola, http://www.scapackaging.com, November 2012.

    [5] Patrik Törmänen and Hussein Jaffal. Reducing electricity cost - case study. Technical report, UMIT Research Lab, Umeå University, 2011.2

  • 191.
    Bjorklund, Johanna
    et al.
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Fernau, Henning
    Kasprzik, Anna
    Polynomial inference of universal automata from membership and equivalence queries2016In: Information and Computation, ISSN 0890-5401, E-ISSN 1090-2651, Vol. 246, p. 3-19Article in journal (Refereed)
    Abstract [en]

    A MAT learning algorithm is presented that infers the universal automaton (UA) for a regular target language, using a polynomial number of queries with respect to that automaton. The UA is one of several canonical characterizations for regular languages. Our learner is based on the concept of an observation table, which seems to be particularly fitting for this computational model, and the necessary definitions are adapted from the literature to the case of UA. 

  • 192.
    Bjorklund, Johanna
    et al.
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Zechner, Niklas
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    My name is legion: estimating author counts based on stylistic diversity2016In: 2016 European intelligence and security informatics conference (EISIC) / [ed] Brynielsson J., Johansson F., IEEE , 2016, p. 108-111Conference paper (Refereed)
    Abstract [en]

    Online propaganda is a growing concern. Fraudulent users write under multiple signatures to give the impression that the opinions they promote are more widespread than they really are, or held by a different demography. The problem as such is not new, but it is becoming increasingly organised and therefore has effects on a larger scale. In this work, we develop methods for assessing the true number of authors of a body of work, to detect artificially inflated user sets. The assessments are based on stylistic richness, here measured as the number of unique features (e.g., words or syntactic fragments) divided by the sum of all features. Initial results suggest that the order of magnitude can be reliable estimated. It is for example possible to differentiate the works of hundreds and thousands of writers.

  • 193.
    Bjuhr, Marcus
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    VARN  Ett nätverksbaserat 2D-actionmultiplayerspel skrivet i Java.2010Independent thesis Basic level (degree of Bachelor), 10 credits / 15 HE creditsStudent thesis
    Abstract [en]

    VARN A network multiplayer 2D action game written in Java. All games that support any form of play across networks is in one way or another affected by the delay, or "ping", that occurs from the time it takes for information to travel over the wires. Not only does it take time, it varies depending on how far away the connected partner is and the current status of the network you are on. Through the years a lot of different methods have been developed to combat these delays. I have reviewed some of these methods and implemented a synchronization system in Java meant to be used in online action multiplayer games.

  • 194.
    Björklund, Anna
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    NoSQL Database for Software Project Data2011Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The field of databases have exploded in the last couple of years. New architectures try to meet the need to store more and more data and new kinds of data. The old relational model is no longer the only way and the NoSQL movement is not a trend but a new way of making the database fit the data, not the other way around.This master thesis report aims to find an efficient and well designed solution for storing and retrieving huge amounts of software project data at Tieto. It starts by looking at different architectures and trying three to see if any of them can solve the problem. The three databases selected are the relational database PostgreSQL, the graph database Neo4j and the key value store Berkeley DB. These are all implemented as a Web service and time is measured to find out which, if any, can handle the data at Tieto. In the end it is clear that the best database for Tieto is Berkeley DB. Even if Neo4j is almost as fast, it is still new and not as mature as Berkeley DB.

  • 195.
    Björklund, Henrik
    et al.
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Berglund, Martin
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Petter, Ericson
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Uniform vs. Nonuniform Membership for Mildly Context-Sensitive Languages: A Brief Survey2016In: Algorithms, ISSN 1999-4893, E-ISSN 1999-4893, Vol. 9, no 2, article id 32Article in journal (Refereed)
    Abstract [en]

    Parsing for mildly context-sensitive language formalisms is an important area within natural language processing. While the complexity of the parsing problem for some such formalisms is known to be polynomial, this is not the case for all of them. This article presents a series of results regarding the complexity of parsing for linear context-free rewriting systems and deterministic tree-walking transducers. We discuss the difference between uniform and nonuniform complexity measures and how parameterized complexity theory can be used to investigate how different aspects of the formalisms influence how hard the parsing problem is. The main results we survey are all hardness results and indicate that parsing is hard even for relatively small values of parameters such as rank and fan-out in a rewriting system.

  • 196.
    Björklund, Henrik
    et al.
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Björklund, Johanna
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Ericson, Petter
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Minimisation and Characterisation of Order-Preserving DAG Grammars2018Report (Other academic)
    Abstract [en]

    Order-preserving DAG grammars (OPDGs) is a formalism for processing semantic infor- mation in natural languages [5, 4]. OPDGs are sufficiently expressive to model abstract meaning representations, a graph-based form of semantic representation in which nodes en- code objects and edges relations. At the same time, they allow for efficient parsing in the uniform setting, where both the grammar and subject graph are taken as part of the input.

    In this article, we introduce an initial algebra semantic for OPDGs, which allows us to view them as regular tree grammars. This makes it possible to transfer a number of results from that domain to OPDGs, both in the unweighted and the weighted case. In particular, we show that deterministic OPDGs can be minimised efficiently, and that they are learnable in the so-called MAT setting. To conclude, we show that the languages generated by OPDGs are MSO-definable.

  • 197.
    Björklund, Henrik
    et al.
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Björklund, Johanna
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Ericson, Petter
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    On the Regularity and Learnability of Ordered DAG Languages2017In: Implementation and Application of Automata: 22nd International Conference, CIAA 2017, Marne-la-Vallée, France, June 27-30, 2017, Proceedings / [ed] Arnaud Carayol and Cyril Nicaud, Cham, 2017, p. 27-39Conference paper (Refereed)
    Abstract [en]

    Order-Preserving DAG Grammars (OPDGs) is a subclass of Hyper-Edge Replacement Grammars that can be parsed in polynomial time. Their associated class of languages is known as Ordered DAG Lan- guages, and the graphs they generate are characterised by being acyclic, rooted, and having a natural order on their nodes. OPDGs are useful in natural-language processing to model abstract meaning representa- tions. We state and prove a Myhill-Nerode theorem for ordered DAG languages, and translate it into a MAT-learning algorithm for the same class. The algorithm infers a minimal OPDG G for the target language in time polynomial in G and the samples provided by the MAT oracle. 

  • 198.
    Björklund, Henrik
    et al.
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Björklund, Johanna
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Zechner, Niklas
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Compression of finite-state automata through failure transitions2014In: Theoretical Computer Science, ISSN 0304-3975, E-ISSN 1879-2294, Vol. 557, p. 87-100Article in journal (Refereed)
    Abstract [en]

    Several linear-time algorithms for automata-based pattern matching rely on failure transitions for efficient back-tracking. Like epsilon transitions, failure transition do not consume input symbols, but unlike them, they may only be taken when no other transition is applicable. At a semantic level, this conveniently models catch-all clauses and allows for compact language representation.

    This work investigates the transition-reduction problem for deterministic finite-state automata (DFA). The input is a DFA A and an integer k. The question is whether k or more transitions can be saved by replacing regular transitions with failure transitions. We show that while the problem is NP-complete, there are approximation techniques and heuristics that mitigate the computational complexity. We conclude by demonstrating the computational difficulty of two related minimisation problems, thereby cancelling the ongoing search for efficient algorithms.

  • 199.
    Björklund, Henrik
    et al.
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Drewes, Frank
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Ericson, Petter
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Between a Rock and a Hard Place: Parsing for Hyperege Replacement DAG Grammars2016In: Proc. 10th International Conference on Language and Automata Theory and Applications (LATA 2016) / [ed] A.H. Dediu, J. Janoušek, C. Martín-Vide, and B. Truthe, Springer Publishing Company, 2016, Vol. 9618, p. 521-532Conference paper (Refereed)
    Abstract [en]

    Motivated by applications in natural language processing, we study the uniform membership problem for hyperedge-replacement grammars that generate directed acyclic graphs. Our major result is a low-degree polynomial-time algorithm that solves the uniform membership problem for a restricted type of such grammars. We motivate the necessity of the restrictions by two different NP-completeness results.

  • 200.
    Björklund, Henrik
    et al.
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Drewes, Frank
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Ericson, Petter
    Umeå University, Faculty of Science and Technology, Department of Computing Science.
    Parsing Weighted Order-Preserving Hyperedge Replacement Grammars2019In: Proceedings of the 16th Meeting on the Mathematics of Language / [ed] F. Drewes, P. de Groote, G. Penn, Association for Computational Linguistics, 2019, p. 1-11Conference paper (Refereed)
    Abstract [en]

    We introduce a weighted extension of the recently proposed notion oforder-preserving hyperedge-replacement grammars and prove that the weightof a graph according to such a weighted graph grammar can be computeduniformly in quadratic time (under assumptions made precise in the paper).

1234567 151 - 200 of 1839
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