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.

The notion of an audio/video (AV) database is introduced. An AV database is a collection of AV values such as digital audio and video data and AV activities such as interconnectable components used to process AV values. Two abstraction mechanisms, temporal composition and flow composition, allow the aggregation of AV values and AV activities respectively. An object-oriented framework, incorporating an AV data model and prescribing AV database/application interaction, is described.>

In this paper we present an object-oriented perspective to multimedia and discuss an approach for prototyping distributed multimedia applications.We describe the implementation of a component kit, an example application, called a virtual museum, and a visual composition tool.The tool allows interactive construction of multimedia applications from generic software components by direct manipulation and graphical editing.

Video widgets are user-interface components rendered with video information.The implementation and several usage examples of a family of video widgets, called video actors,, are presented.Video actors rely on two capabilities of digital video: non-linear access, and the layering of video information.Non-linear access allows video frames to be displayed in mbitrary order without loss of continuity, layering allows two or more video streams to be spatially composed.Both capabilities are now becoming available to user-interface designers.

Abstract Multimedia applications can be seen as sets of autonomous parts, independent yet capable of working together. This assumption allows for the construction of multimedia applications in a “connectionist” fashion. In this paper we describe mechanisms for the visual composition of multimedia applications. These mechanisms allow for quick and flexible application construction by direct manipulation with reference to multiple composition models. An object‐oriented framework for multimedia systems will be introduced throughout the paper.

Object-orientation offers more than just objects, classes and inheritance as means to structure applications. It is an approach to application development in which software systems can be constructed by composing and refining pre-designed, plug-compatible software components. But for this approach to be successfully applied, programming languages must provide better support for component specification and software composition, the software development life-cycle must separate the issues of generic component design and reuse from that of constructing applications to meet specific requirements, and, more generally, the way we develop, manage, exchange and market software must adapt to better support large-scale reuse for software communities. In this paper we shall explore these themes and we will highlight a number of key research directions and open problems to be explored as steps towards improving the effectiveness of object technology.

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. 1. Introduction The improving capabilities of multimedia workstations, combined with the development of multimedia recording formats (for example, CD-I and DVI, see [14] for a recent description) is likely to increase the demand for applications involving multimedia. However the development of multimedia applications is presently hampered by two key problems: First, multimedia involves concepts from audio recording, video production, animation, and music -- concepts that are novel to many programmers. Second, multimedia operations of...

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.

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 algorithm's 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.

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.

Most object-oriented systems lack two useful facilities: the ability of objects to migrate to new environments and the ability of objects to acquire new operations dynamically. This paper proposes Knos, an object-oriented environment that supports these actions. Knos' operations, data structures, and communication mechanisms are discussed. Knos objects “learn” by exporting and importing new or modified operations. The use of such objects as intellectual support tools is outlined. In particular, various applications involving cooperation, negotiation, and apprenticeship among objects are described.

Several problems of document presentation and query, formulation arising in systems dealing with multimedia documents are discussed. Examples from a prototype distributed multimedia document filing system are described.

A data model for representing the structure and semantics of office objects is proposed.The model contains features for modeling forms, documents, and other complex objects; these features include a constraint mechanism based on triggers, templates for presenting objects in different media, and unformatted data types such as text and audio.The representation of common office objects is described.User-level commands may be translated to operations within the model.

Message systems send and receive messages but do not manage the information the messages contain. Database management systems manage the information of a global database but do not have a notion of address. In this paper the authors outline a prototype system which integrates the facilities of message systems and database management systems. The system manages structured messages according to their contents. The messages can be stored within a station and transferred between stations. Information present in the messages can be queried in a distributed manner. Message structure can also be exploited by automatic procedures which recognize triggering conditions and perform user specified actions.