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Journals  Conferences  Reports

  1. Koster, C.H.A. and Weide, Th.P. van der, Hairy Search Trees. The Computer Journal, Nr: 8, Vol: 38, Pages: 691-694, 1995

    Random search trees have the property that their depth depends on the order in which they are built. They have to be balanced in order to obtain a more efficient storage-and-retrieval data structure. Balancing a search tree is time consuming. This explains the popularity of data structures which approximate a balanced tree but have lower amortised balancing costs, such as AVL trees, Fibonacci trees and 2-3 trees. The algorithms for maintaining these data structures efficiently are complex and hard to derive. This observation has led to insertion algorithms that perform local balancing around the newly inserted node, without backtracking on the search path. This is also called a fringe heuristic. The resulting class of trees is referred to as 1-locally balanced trees, in this note referred to as hairy trees. In this note a simple analysis of their behaviour is povided.

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  2. Proper, H.A. and Weide, Th.P. van der, Information Disclosure in Evolving Information Systems: Taking a shot at a moving target. Data & Knowledge Engineering, Vol: 15, Pages: 135-168, 1995

    In this paper, we introduce a query language for evolving information systems. Evolving information systems go beyond the capacity of conventional database systems, not only as they incorporate a time dimension, but also since they allow all aspects of the system to evolve.

    The introduced language is related to the philosophy underlying NIAM (Natural language Information Analysis Method). This method investigates the grammar of the communication in the Universe of Discourse. Usually this grammar is depicted as an information structure diagram (NIAM or ER schema).

    This paper describes the language Elisa-D, which is based on this grammar. As a result, expressions in this language have a direct meaning in the universe of discourse, while natural language expressions are easily formalised in this language.

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  3. Proper, H.A. and Weide, Th.P. van der, A General Theory for the Evolution of Application Models. IEEE Transactions on Knowledge and Data Engineering, Nr: 6, Vol: 7, Pages: 984-996, December, 1995

    In this article we focus on evolving information systems. First a delimitation of the concept of evolution is provided, resulting in a first attempt to a general theory for such evolutions.

    The theory makes a distinction between the underlying information structure at the conceptual level, its evolution on the one hand, and the description and semantics of operations on the information structure and its population on the other hand. Main issues within this theory are object typing, type relatedness and identification of objects. In terms of these concepts, we propose some axioms on the well-formedness of evolution.

    In this general theory, the underlying data model is a parameter, making the theory applicable for a wide range of modelling techniques, including object-role modelling and object oriented techniques.

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Journals  Conferences  Reports

  1. Berger, F.C. and Weide, Th.P. van der, A Feedback Mechanism for Query by Navigation. Proceedings of the Sixth Australasian Database Conference, ADC`95, Edited by: R. Sacks-Davis, and J. Zobel. Australian Computer Science Communications, Vol: 17(2), Pages: 56-65, January, 1995

    The Two-Level Hypermedia Paradigm sees an Information Retrieval System as consisting of a document network (the Hyperbase) and a descriptor (term) network (the Hyperindex). Query by Navigation is a process whereby the searcher gives a description of the Information Need by travelling through the descriptor network. This paper presents a formalism for expressing the effects of traversing the Hyperindex on the elements of the Hyperindex. This formalism makes use of probabilities for modelling the searcher's behavious. The events which can occur during the search process are discussed and modelled. Some important properties, which are reasonable to demand of a retrieval system, can be proven to be valid if this formalism is adopted. A mechanism for assigning a measure of relevance to documents is presented. This uses the formalism mentioned above. An example will show the effectiveness of The aspect of relevance feedback and its role in Query by Navigation is introduced by examining the different level on which the searcher can offer information for weeding out unwanted sections of the search space. In order to illustrate the workings of Query by Navigation a small example is included.

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  2. Hofstede, A.H.M. ter and Proper, H.A. and Weide, Th.P. van der, Computer Supported Query Formulation in an Evolving Context. Proceedings of the Sixth Australasian Database Conference, ADC`95, Edited by: R. Sacks-Davis, and J. Zobel. Australian Computer Science Communications, Vol: 17(2), Pages: 188-202, January, 1995

    Even if high-level query languages are used, query formulation may cause problems. This is notably so in case of large and complex application domains. Typical examples of these kinds of application domains are evolving application domains. In an evolving application domain not only populations may change, but also the conceptual schema. Even more, the history of the application domain should be recorded, and be retrievable.

    This paper focuses on support for query formulation in the context of large conceptual schemata. The solution presented uses the idea of query-by-navigation in conjunction with query-by-construction. First this idea is illustrated by means of some examples, then it is formally defined.

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Journals  Conferences  Reports

  1. Frederiks, P.J.M. and Weide, Th.P. van der, Fundamentals of Object Orientation in KISS. Technical report: CSI-N9601, May, Computing Science Institute, University of Nijmegen, 1995

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  2. Frederiks, P.J.M. and Koster, C.H.A. and Weide, Th.P. van der, Object-Oriented Analysis using Informal Language. Technical report: CSI-R9516, December, Computing Science Institute, University of Nijmegen, Nijmegen, The Netherlands, 1995

    In this paper we study one aspect of the analysis of information systems, viz., how to obtain a (formal) model using informal formulations. We give a general framework for this modeling process, and also discuss the cognitive identity of domain experts. The starting point of the modeling process is a set of formulations (intended as an informal specification). Initially, these formulations need not form a complete and consistent specification. In an iterative process, alternating deduction and induction, an informal specification and corresponding formal model are to be derived. Rather than aiming at one (large) model, certain partial models are derived that collectively describe the application domain in a complete and consistent fashion. This process involves both domain expert and system analyst, communicating primarily in natural language.

    This communication is supported by a system analyzing informal formulations to obtain fragments of the (formal) model, and paraphrasing fragments of this model to obtain feedback. This feedback mechanism is intended to support the validation of the model, regarding both structural aspects and constraints on populations.

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  3. Hofstede, A.H.M. ter and Lippe, E. and Weide, Th.P. van der, A Categorical Framework for Conceptual Data Modeling: Definition, Application, and Implementation. Technical report: CSI-R9512, November, Computing Science Institute, University of Nijmegen, Nijmegen, The Netherlands, 1995

    For successful information systems development, conceptual data modeling is essential. Nowadays a plethora of techniques for conceptual data modeling exist. Many of these techniques lack a formal foundation and a lot of theory, e.g. concerning updates or schema transformations, is highly data model specific. As such there is a need for a unifying formal framework providing a sufficiently high level of abstraction. In this paper the use of category theory for this purpose is addressed. Well­known conceptual data modeling concepts, such as relationship types, generalization, specialization, and collection types are discussed from a categorical point of view. An important advantage of this framework is its ``configurable semantics''. Features such as null values, uncertainty, and temporal behavior can be added by selecting appropriate instance categories. The addition of these features usually requires a complete redesign of the formalization in traditional set­based approaches to semantics. Applications of the framework in the context of schema transformations and improved automated modeling support are discussed.

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  4. Hofstede, A.H.M. ter and Bosman, F.J.M. and Weide, Th.P. van der, Toward a Data Modeling Shell. Technical report: CSI-R9513, November, Computing Science Institute, University of Nijmegen, Nijmegen, The Netherlands, 1995

    Much research has been performed into improved automated modeling support. Ideally, a modeling support environment is highly flexible and allows analysts to define their own concepts and ways of working. While in general this seems an unattainable goal, for specific types of modeling techniques this might be achieved. In this paper, a data modeling shell is discussed which is based on a framework for conceptual data modeling techniques embedded in category theory. An important property of the framework is its ``configurablesemantics'', which means that features such as null values, uncertainty, and temporal behavior can be added by selecting appropriate instance categories. Hence, the data modeling shell not only allows syntactic conventions, including representational aspects, to be customized for a conceptual data modeling technique, it also allows a choice of required semantic features.

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  5. Ven, E.S.C. van de and Bommel, P. van and Frederiks, P.J.M. and Weide, Th.P. van der, Natural Language Properties and Information Systems. Technical report: CSI-N9608, Computing Science Institute, University of Nijmegen, 1995

    In this paper the concept of natural language is discussed from three perspectives: which properties does natural language have from a psychologic point of view, how are natural language sentences built, and what is their meaning? The paper serves as a basis for applying natural language in information systems engineering.

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  6. Verhoef, T.F. and Weide, Th.P. van der, Gerichte ondersteuning voor systeemontwikkeling met bouwstenen. Technical report: CSI-N9501, Maart, Radboud University Nijmegen, 1995

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