Dennis Tsichritzis

Component-oriented software development

Object-oriented programming techniques promote a new approach to software engineering in which reliable, open applications can be lar gely constructed, rather than programmed, by reusing “frameworks” [3] of plug-compatible software components. Although the dream of a components-based software industry is very old [9], only now does it appear that we are close to realizing the dream. The reason for this is twofold: • Modern applications are increasingly open in terms of topology, platform and evolution, and so the need for a component-oriented approach to development is even more acute than in the past; • Objects provide an organizational paradigm for decomposing large applications into cooperating objects as well as a reuse paradigm for composing applications from pre-packaged software components. Despite the contributions of object-oriented technology , there are several open research problems that must be resolved to reach the goal of ef f ctive component-oriented development. First, object-oriented mechanisms for composition and reuse must be cleanly integrated with other features, such as concurrency , persistence and distribution. Second, ef fective reuse of software presupposes the existence of tools to support the organisation and retrieval of components according to application requirements and the interactive construction of running applications from components. Third, the design of reusable frameworks is an iterative, evolutionary process, so it is necessary to manage software and software information in such a way that designs and implementations can evolve gracefully. Finally, present object-oriented methodologies do not explicitly address the design of reusable frameworks. Not only the languages and tools, but the economics, methods and culture of software development must ultimately adapt to a new evolutionary software life-cycle if we are to realize the benefits of large-scale software reuse [2][17].

Form management

This paper consists of three interrelated parts. In the first part forms are intoduced as an abstraction and generalization of business paper forms. A set of facilities for the manipulation of forms and their contents is outlined. Forms can be created, stored, found, viewed in different media, mailed, and located by office workers. Data on forms can also be processed in a completely integrated way. The facilities are discussed both abstractly and in relation to a prototype system. In the second part a facility is outlined for the specification and implementation of automatic form procedures. These procedures specify actions on forms which are triggered automatically when certain preconditions are met. The preconditions, actions, and specification method are based on forms. The discussion is centered on our implementation of such a specification framework. Finally, in the third part, techniques for the analysis of office flow are specified. An algorithm is outlined for the categorization of forms into classes depending on the local routing and actions on the forms. In this way, we can obtain the paths that forms take and analyze the system for correctness and loading characteristics.

The dynamics of innovation

Research always brings to mind the paradigm of an absent-minded scientist playing aimlessly with his pencil (and computer) seeking some universal truth. It is a paradigm that gave us, over the centuries, great progress in science, and it resulted in relative prosperity for mankind. The basis for this paradigm was and still is that the researcher is highly intelligent, self-motivated, and rather undisciplined. Can we go to the next millennium with this paradigm? In a society where everything is measured, quantified, and rationalized, how can researchers continue to live in an idealistic world? We already see the signs of trouble. Research budgets and research institutes are under pressure in both the public and private sectors. This is the time to revise our position, especially in the fast-moving area of information technology.

Reengineering the university

new concepts. The Internet allows virtual classrooms. Digital libraries provide knowledge repositories. The Web offers up-to-date material for seminar discussions. Computer simulation substitutes for laboratories. Technology is not simply an add-on service as computers or audiovisual were before—it touches the very substance of the university, that is, knowledge development and transfer. A complete reengineering has to take place in order to retain the spirit of the university as an intellectual watering hole. The crisis in universities is both financial and structural. Most universities around the world are still largely dependent on public financing, but educational funds are drying up due to the general tightening in governmental budgets. In addition, academic research funds are also being cut. Governments frequently question the economic value of academic research. Meanwhile, companies are buying only relevant research and Universities are due for a radical restructuring. After centuries of evolu-

Data modeling of time-based media

Many aspects of time-based media—complex data encoding, compression, “quality factors,” timing—appear problematic from a data modeling standpoint. This paper proposes timed streams as the basic abstraction for modeling time-based media. Several media-independent structuring mechanisms are introduced and a data model is presented which, rather than leaving the interpretation of multimedia data to applications, addresses the complex organization and relationships present in multimedia.

Class management for software communities

Object-oriented programming may engender an approach to software development characterized by the large-scale reuse of object classes. Large-scale reuse is the use of a class not just by its original developers, but by other developers who may be from other organizations, and may use the classes over a long period of time. Our hypothesis is that the successful dissemination and reuse of classes requires a well-organized community of developers who are ready to share ideas, methods, tools and code. Furthermore, these communities should be supported by software information systems which manage and provide access to class collections. In the following sections we motivate the need for software communities and software information systems. The bulk of this article discusses various issues associated with managing the very large class collections produced and used by these communities.

Hierarchical Data-Base Management: A Survey

This survey paper discusses the facilities provided by hierarchical data-base management systems. The systems are based on the hierarchical data model which is defined as a special case of the network data model. Different methods used to access hierarchically organized data are outlined. Constructs and examples of programming languages are presented to illustrate the features of hierarchical systems. This is followed by a discussion of techniques for implementing such systems. Finally, a brief comparison is made between the hierarchical, the network, and the relational systems.

Message files

We describe a message-filing capability which allows for the retrieval of messages according to contents. Messages are organized in large, general files such that frequent reorganization is avoided. The user specifies a filter which restricts the attention to a manageable subset of messages. Messages within the subset are retrieved for a final check. We discuss file organization and access method, as well as performance and implementation considerations.

Muse: A Multimedia Filing System

New technology is changing the way we store documents. This experimental system features flexible document retrieval, a distributed architecture, and the capacity to store many very large documents.

A unified approach to functional dependencies and relations

In Codds relational model, the relation name groups together a family of functional dependencies over a set of attributes. For integrity and for maintenance purposes it is important to eliminate inherent redundancy within a relation due to the repetition of instances of a functional connection between attributes. This led Codd to propose a series of three normalizations. The manipulation of normal forms is governed by functional dependencies that are explicitly declared to exist within the relation. Since functional dependencies completely govern the decomposition rules of normalization, perhaps it is more sensible to take them as the elementary notions to be later synthesized into more complex structures, such as relations. Our goals, then are twofold. First, we will discuss how the use of functional dependencies lends itself to a rigorous and correct, yet clear and simple description of complex data relationships. Second, we will outline some new computational techniques to map functional dependencies into normal form relations algorithmically, thus allowing us to use the dependencies as a basic unit on the implementation as well as conceptual level.