Klaus-Dieter Schewe

Conceptual modelling of web information systems

This paper presents the conceptual modelling parts of a methodology for the design of large-scale data-intensive web information systems (WISs) that is based on an abstract abstraction layer model (ALM). It concentrates on the two most important layers in this model: a business layer and a conceptual layer.The major activities on the business layer deal with user profiling and storyboarding, which addresses the design of an underlying application story. The core of such a story can be expressed by a directed multigraph, in which the vertices represent scenes and the edges actions by the users including navigation. This leads to story algebras which can then be used to personalise the WIS to the needs of a user with a particular profile.The major activities on the conceptual layer address the support of scenes by modelling media types, which combine links to databases via extended views with the generation of navigation structures, operations supporting the activities in the storyboard, hierarchical presentations, and adaptivity to users, end-devices and channels.

Semantics in databases

The term “Semantics” is one of the overloaded in computer science and used in various meaning. This variety can also be observed in database literature. In computer linguistics or web research, semantics is a component of the language which associates words or components of a grammar with their meaning (linguistic content). In modeling and specification, semantics assigns set-theoretic denotations to formulas in order to characterize truth. At the same time, semantics is used as the basis for certain methods of proof (truth and proof semantics in semiotics). In programming language technology, semantics is often used in the sense of operational semantics, i.e. consists in an interpretation of commands of a programming language by machine operations. This widespread usage of the term “semantics” has led to very different goals, methods, and applications. Semantics includes at the same time the interpretation of utterances, temporal, contextual, subjective and other aspects. Semantics is either considered operationally on the basis of applications or implementations, or logically associating a database state or a collection of database states to a truth value or pragmatically by relating utterances to the understanding of the user. These three understandings may be mapped to each other.

Design of data-intensive Web-based information services

One common usage of the WWW is to provide information services, e.g. for regional event calenders, university lecture management, travel information, etc. Their design requires a clear picture of the systems usage and the supported technical environment. The core of the problem is to provide flexible access units based on extended views on some underlying database. The extension consists of escort information, links, operational facilities and means for the generation of different presentations. We call such units media objects. In order to also allow a flexible presentation for them, we adapt the metaphor of a container. In this way it is possible to present the same information in various ways depending on the user profile and the possible technical restrictions of the display device.

Integrating database and dialogue design

Abstract. The user interface of data-intensive information systems may be described as a collection of semi-independent dialogues with underlying procedures accessing databases. It will be shown how to conceptualize dialogues via dialogue objects. These are organized in an object oriented fashion by dialogue classes modelled as extended database views. The description is based on an object oriented model which enables a smooth integration of dialogues with the underlying database schema.The resulting integrated model can serve as a unifying conceptual umbrella encompassing both databases and user-interfaces. The only remaining task for the presentation layer consists of suitable ergonomic presentations of dialogue objects on the screen by means of a general user interface management system.This approach may help in the development of information systems that aim at the support of highly skilled users. The design of such systems has to cope with the specific work conditions as being self-organized, equipped with certain duties and responsibilities and dependent on some environmental knowledge. Such systems are supposed to leave fundamental decisions to their users, e.g. to continue or interrupt a certain piece of work or to switch from one application to another in order to achieve a seamless embedding in organisational processes and work flow.

Modeling Interaction and Media Objects

Interaction of users with computational devices has to meet the u sers intention on one side and needs to be specified in a formal manner which can be uniquely interpreted by computers. Thus, we need a model of interaction which meets the intensional understanding of users and which has an extensional description that is directly implementable. In this paper we develop a model for interaction on the basis of the notion of interaction objects. We show further how this notion can be specialized to internet-based interaction. In the later case we use media objects for interaction.

Reasoning About Web Information Systems Using Story Algebras

As web information systems (WIS) tend to become large, it becomes decisive that the underlying application story is well designed. Such stories can be expressed by a process algebra. In this paper we show that such WIS-oriented process algebras lead to many-sorted Kleene algebras with tests, where the sorts correspond to scenes in the story space. As Kleene algebras with tests subsume propositional Hoare logic, they are an ideal candidate for reasoning about the story space. We show two applications for this: (1) the personalisation of the story space to the preferences of a particular user, and (2) the satisfaction of particular information needs of a WIS user.

Axiomatisations of functional dependencies in the presence of records, lists, sets and multisets

We investigate functional dependencies in databases that support complex values such as records, lists, sets anu multisets. Therefore, an abstract algebraic framework is proposed that classifies data models according to the underlying types they support. This allows to emphasise the impact of the data types rather than the specifics of a particular data model.The main results are finite, minimal, sound and complete sets of inference rules for the implication of functional dependencies in the presence of records and all combinations of lists, sets and multisets. The inference rules are similar to Armstrongs original axioms for the relational data model, thanks to the algebraic framework. The completeness result, however, requires a deep analysis in the case of sets and, in particular, multisets.

Modelling Data Warehouses and OLAP Applications by Means of Dialogue Objects

The idea of data warehouses is to provide condensed information in order to support managers in the analysis of business facts such as sales, costs, profits, etc.alon g various dimensions such as geography, organisation, time, etc. The analysis should allow fast switches between different selected multiple dimensions at different granularity. The task itself is usually called on-line analytical processing (OLAP). We show in this paper how to model data warehouses with OLAP functionality by means of dialogue objects. These are extended and possibly materialised views on collections of operative databases and couple structural and behavioural aspects of application units.

A Conceptual View of Web-Based E-Learning Systems

Starting from a general framework for web-based e-learning systems that is based on an abstraction layer model, this paper presents a conceptual modelling approach, which captures the modelling of learners, the modelling of courses, the personalisation of courses, and the management of data in e-learning systems. Courses are modelled by outline graphs, which are further refined by some form of process algebra. The linguistic analysis of word fields referring to an application domain helps to set up these course outlines. Learners are modelled by classifying value combinations for their characteristic properties. Each learner type gives rise to intentions as well as rights and obligations in using a learning system. Intentions can be formalised as postconditions, while rights and obligations lead to deontic constraints. The intentions can be used for the personalisation of the learning system to a learner type. Finally, the management of data in an e-learning system is approached on two different levels dealing with the content of individual learning units and the integrated content of the whole system, respectively. This leads to supporting databases and views defined on them.

Functional and multivalued dependencies in nested databases generated by record and list constructor

The impact of the list constructor on two important classes of relational dependencies is investigated. Lists represent an inevitable data structure whenever order matters and data is allowed to occur repeatedly. The list constructor is therefore supported by many advanced data models such as genomic sequence, deductive and object-oriented data models including XML. The article proposes finite axiomatisations of functional, multivalued and both functional and multivalued dependencies in nested databases supporting record and list constructor. In order to capture different data models at a time, an abstract algebraic approach based on nested attributes is taken. The presence of the list constructor calls for a new inference rule which allows to infer non-trivial functional dependencies from multivalued dependencies. Further differences to the relational theory become apparent when the independence of the inference rules is investigated. The extension of the relational theory to nested databases allows to specify more real-world constraints and increases therefore the number of application domains.