Simon J. Gibbs

Groupware: some issues and experiences

Groupware reflects a change in emphasis from using the computer to solve problems to using the computer to facilitate human interaction. This article describes categories and examples of groupware and discusses some underlying research and development issues. GROVE, a novel group editor, is explained in some detail as a salient groupware example

Concurrency control in groupware systems

Groupware systems are computer-based systems that support two or more users engaged in a common task, and that provide an interface to a shared environment. These systems frequently require fine-granularity sharing of data and fast response times. This paper distinguishes real-time groupware systems from other multi-user systems and discusses their concurrency control requirements. An algorithm for concurrency control in real-time groupware systems is then presented. The advantages of this algorithm are its simplicity of use and its responsiveness: users can operate directly on the data without obtaining locks. The algorithm must know some semantics of the operations. However the algorithms overall structure is independent of the semantic information, allowing the algorithm to be adapted to many situations. An example application of the algorithm to group text editing is given, along with a sketch of its proof of correctness in this particular case. We note that the behavior desired in many of these systems is non-serializable.

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].

Composite multimedia and active objects

An object-oriented framework for composite multimedia is described. In analogy to constructing complex graphics entities from graphics primitives and geometric transformations, composite multimedia is constructed from multimedia primitives and temporal transformations. Active objects based on real-time processes are proposed as multimedia primitives. Their combination to form composite multimedia and the requisite temporal transformations are illustrated.

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.

Query processing in a multimedia document system

Query processing in a multimedia document system is described. Multimedia documents are information objects containing formatted data, text, image, graphics, and voice. The query language is based on a conceptual document model that allows the users to formulate queries on both document content and structure. The architecture of the system is outlined, with focus on the storage organization in which both optical and magnetic devices can coexist. Query processing and the different strategies evaluated by our optimization algorithm are discussed.

LIZA: an extensible groupware toolkit

Software for supporting groups of cooperating users — groupware — raises a number of new issues in user interface design. This paper gives a definition of groupware and presents a model of group tools based on active objects. The model has been applied to the design and implementation of an extensible groupware toolkit known as LIZA. The paper describes the architecture of LIZA. Examples of group tools running under LIZA are used to illustrate some of the problems in the design of multi-user interfaces.

Virtual studios: an overview

Virtual studio systems began as experimental prototypes that extended traditional chromakeying. Now commercial products based on graphics supercomputers are commonly used for broadcast production. We discuss this evolution and consider extensions, alternative approaches, and issues facing broadcasters who introduce virtual studio systems.

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.