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Distributed systems has been an area of intense activity over the past ten years. The subject is entering a stage of maturity with work now focussing on standards for Open Distributed Processing (ODP). However, it is important that standardisation is responsive to new demands on the technology. This is especially true with the emergence of high speed networks in general and multimedia computing in particular. This paper describes research into handling multimedia in the Advanced Networked Systems Architecture (ANSA), a state of the art distributed platform. It is shown that ANSA, although comprehensive in scope, fails to explicitly address multimedia requirements. A number of specific extensions are proposed to remedy these omissions. These include streams, as an abstraction over multimedia protocols, and chains, as a generic control interface to multimedia devices (including storage servers). Importantly, the proposed extensions do not affect the core ANSA architecture, but instead ad...

We propose a framework for the specification of extensible database systems. A particular goal is to implement a software component for parsing and rule-based optimization that can be used with widely varying data models and query languages as well as representation and query processing systems. The key idea is to use second-order signature (and algebra), a system of two coupled many-sorted signatures, where the top-level signature offers kinds and type constructors and the bottom-level signature provides polymorphic operations over the types defined as terms of the top level. Hence the top level can be used to define a data or representation model and the bottom level to describe a query algebra or a query processing algebra. We show the applicability of this framework by examples drawn from relational modeling and query processing.

this paper is to show how a collection of specification constructs may be formally defined that supports the former effort. We should stress that we shall not attempt to provide a full and practical specification language that can be used for object-oriented design. We shall have to limit ourselves to concentrate on the definition of our main primitive of specification (formalising the notion of object) together with two well known specification constructs: inheritance and aggregation (complex objects). However, we do not see deep problems in extending our results to other useful constructs such as class/type grouping and parameterisation.

The use of hierarchy is an important component of object-oriented design. Hierarchy allows the use of type families, in which higher level supertypes capture the behavior that all of their subtypes have in common. For this methodology to be effective, it is necessary to have a clear understanding of how subtypes and supertypes are related. This paper takes the position that the relationship should ensure that any property proved about supertype objects also holds for its subtype objects. It presents two ways of defining the subtype relation, each of which meets this criterion, and each of which is easy for programmers to use. The subtype relation is based on the specifications of the sub- and supertypes; the paper presents a way of specifying types that makes it convenient to define the subtype relation. The paper also discusses the ramifications of this notion of subtyping on the design of type families. 1 Introduction What does it mean for one type to be a subtype of another? We arg...

The purpose of this thesis is to investigate a type system for databases and object-oriented programming and to design a statically typed programming language for these applications. Such a language should ideally have a static type system that supports: • polymorphism and static type inference, • rich data structures and operations to represent various data models for databases including the relational model and more recent complex object models, • central features of object-oriented programming including user definable class hierarchies, multiple inheritance, and data abstraction, • the notion of extents and object-identities for object-oriented databases. Without a proper formalism, it is not obvious that the construction of such a type system is possible. This thesis attempts to construct one such formalism and proposes a programming language that uniformly integrate all of the above features. The specific contributions of this thesis include: • A simple semantics for ML polymorphism and axiomatization of the equational theory of ML. • A uniform generalization of the relational model to arbitrary complex database objects that

In this paper we present an extended type system for an object-oriented database language, based uniquely on the set interpretation of object classes. We show that this system has the same expressive power as more complex approaches and is well suited to type inference for programming or querying database languages. 1. Introduction A lot of work has been done to provide object-oriented systems with types that would permit efficient compilation. On the theoretical side, variant records have been added to polymorphic type systems to allow object-oriented forms of programming [Car88][Car89][Mit90]. On the practical side, complex object models have been developed to improve compilation [Wan87][Red88][CHC90][GJ90]. The database community has proposed some powerful type systems to manage complex objects with associated compiling and optimization techniques [Ku85][SZ87][Ja89][AK89]. Investigations to merge logic and objects have also produced interesting type systems [Ait86][GM86][KL89]. How...