84 research outputs found

    Discontinuities in pattern inference

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    This paper deals with the inferrability of classes of E-pattern languages—also referred to as extended or erasing pattern languages—from positive data in Gold’s model of identification in the limit. The first main part of the paper shows that the recently presented negative result on terminal-free E-pattern languages over binary alphabets does not hold for other alphabet sizes, so that the full class of these languages is inferrable from positive data if and only if the corresponding terminal alphabet does not consist of exactly two distinct letters. The second main part yields the insight that the positive result on terminal-free E-pattern languages over alphabets with three or four letters cannot be extended to the class of general E-pattern languages. With regard to larger alphabets, the extensibility remains open. The proof methods developed for these main results do not directly discuss the (non-)existence of appropriate learning strategies, but they deal with structural properties of classes of E-pattern languages, and, in particular, with the problem of finding telltales for these languages. It is shown that the inferrability of classes of E-pattern languages is closely connected to some problems on the ambiguity of morphisms so that the technical contributions of the paper largely consist of combinatorial insights into morphisms in word monoids

    Discontinuities in pattern inference

    Get PDF
    This paper deals with the inferrability of classes of E-pattern languages—also referred to as extended or erasing pattern languages—from positive data in Gold’s model of identification in the limit. The first main part of the paper shows that the recently presented negative result on terminal-free E-pattern languages over binary alphabets does not hold for other alphabet sizes, so that the full class of these languages is inferrable from positive data if and only if the corresponding terminal alphabet does not consist of exactly two distinct letters. The second main part yields the insight that the positive result on terminal-free E-pattern languages over alphabets with three or four letters cannot be extended to the class of general E-pattern languages. With regard to larger alphabets, the extensibility remains open. The proof methods developed for these main results do not directly discuss the (non-)existence of appropriate learning strategies, but they deal with structural properties of classes of E-pattern languages, and, in particular, with the problem of finding telltales for these languages. It is shown that the inferrability of classes of E-pattern languages is closely connected to some problems on the ambiguity of morphisms so that the technical contributions of the paper largely consist of combinatorial insights into morphisms in word monoids

    Conjunctive Queries for Logic-Based Information Extraction

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    This thesis offers two logic-based approaches to conjunctive queries in the context of information extraction. The first and main approach is the introduction of conjunctive query fragments of the logics FC and FC[REG], denoted as FC-CQ and FC[REG]-CQ respectively. FC is a first-order logic based on word equations, where the semantics are defined by limiting the universe to the factors of some finite input word. FC[REG] is FC extended with regular constraints. The second approach is to consider the dynamic complexity of FC.Comment: Based on the author's PhD thesis and contains work from two conference publications (arXiv:2104.04758, arXiv:1909.10869) which are joint work with Dominik D. Freydenberge

    Finding facts vs. browsing knowledge in hypertext systems

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    Efficient Computation of Descriptive Patterns

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    A pattern α\alpha is a word consisting of constants and variables and the pattern language L(α)L(\alpha) (over an alphabet ÎŁ\Sigma) is the set of all words that can be obtained from α\alpha by uniformly replacing the variables with words over ÎŁ\Sigma. We investigate the problem of computing a pattern α\alpha that is descriptive of a given finite set S⊆Σ∗S \subseteq \Sigma^* of words, i.\,e., S⊆L(α)S \subseteq L(\alpha) and there is no other pattern ÎČ\beta with S⊆L(ÎČ)⊂L(α)S \subseteq L(\beta) \subset L(\alpha). A pattern α\alpha that is descriptive of a set SS represents the structural commonalities of the words in SS and, thus, can serve as a classifier with respect to this structure. Furthermore, (polynomial time) computability of descriptive patterns is sufficient for (polynomial time) inductive inference of pattern languages. We investigate the complexity of computing descriptive patterns and, for subclasses of patterns, we present efficient algorithms for computing them

    Effects of automatically updated database documentation on the work tasks of IS professionals and end-users

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    Abstract. This study analysed the effects of automatically generated database documentation on the work tasks of IS professionals and end-users. The effects were analysed with case study approach in one Finnish software company that provides customer information system to their customer companies. The availability of the consistent database documentation was a new situation for both IS professionals in the case company and for the end-users in the customer companies. The case company wished to understand, how the documentation would affect the work tasks of the two stakeholder groups. Database documentation is used for database design and analysis tasks. Database documentation is created in the development phase of an IS and maintained afterwards. Yet, the documentation can end up stagnated and the documentation maintenance is commonly considered a burden for the IS professionals. Database reverse-engineering allows automatic generation of database documentation, thus erasing the manual maintenance of database documentation. The research data was gathered using two separate questionnaires for the end-users and IS professionals. Both qualitative and quantitative data were gathered. The questionnaire’s open questions were analysed using content analysis and closed questions were considered descriptive statistics. According to the findings, database documentation supports both IS professionals’ and end-users’ in their work tasks. Database documentation was considered important for the efficiency of their work tasks. Documentation aids the database users to gain knowledge of the database structure and prevents false interpretations. Database documentation also allows the users to plan work better and to conduct tasks with fewer increments. Additionally, documentation allows a better degree of independent work and gives courage for the employees to familiarize themselves to new parts of the database and information system. The consistent, up-to-date database documentation has positive effects on the work tasks of both IS professionals and end-users. Lower workload, better understanding of the system and less false interpretations indicate that software companies would benefit from documenting their databases in more detail and more consistently, for example, using database reverse-engineering. Consistent database documentation benefits all of the database users

    Pattern matching with variables: Efficient algorithms and complexity results

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    A pattern α (i. e., a string of variables and terminals) matches a word w, if w can be obtained by uniformly replacing the variables of α by terminal words. The respective matching problem, i. e., deciding whether or not a given pattern matches a given word, is generally NP-complete, but can be solved in polynomial-time for restricted classes of patterns. We present efficient algorithms for the matching problem with respect to patterns with a bounded number of repeated variables and patterns with a structural restriction on the order of variables. Furthermore, we show that it is NP-complete to decide, for a given number k and a word w, whether w can be factorised into k distinct factors. As an immediate consequence of this hardness result, the injective version (i. e., different variables are replaced by different words) of the matching problem is NP-complete even for very restricted clases of patterns

    Sketch-based digital storyboards and floor plans for authoring computer-generated film pre-visuals

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    Pre-visualisation is an important tool for planning films during the pre-production phase of filmmaking. Existing pre-visualisation authoring tools do not effectively support the user in authoring pre-visualisations without impairing software usability. These tools require the user to either have programming skills, be experienced in modelling and animation, or use drag-and-drop style interfaces. These interaction methods do not intuitively fit with pre-production activities such as floor planning and storyboarding, and existing tools that apply a storyboarding metaphor do not automatically interpret user sketches. The goal of this research was to investigate how sketch-based user interfaces and methods from computer vision could be used for supporting pre-visualisation authoring using a storyboarding approach. The requirements for such a sketch-based storyboarding tool were determined from literature and an interview with Triggerfish Animation Studios. A framework was developed to support sketch-based pre-visualisation authoring using a storyboarding approach. Algorithms for describing user sketches, recognising objects and performing pose estimation were designed to automatically interpret user sketches. A proof of concept prototype implementation of this framework was evaluated in order to assess its usability benefit. It was found that the participants could author pre-visualisations effectively, efficiently and easily. The results of the usability evaluation also showed that the participants were satisfied with the overall design and usability of the prototype tool. The positive and negative findings of the evaluation were interpreted and combined with existing heuristics in order to create a set of guidelines for designing similar sketch-based pre-visualisation authoring tools that apply the storyboarding approach. The successful implementation of the proof of concept prototype tool provides practical evidence of the feasibility of sketch-based pre-visualisation authoring. The positive results from the usability evaluation established that sketch-based interfacing techniques can be used effectively with a storyboarding approach for authoring pre-visualisations without impairing software usability
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