David Beech

Generalized version control in an object-oriented database

An important function of an engineering database management system is to support incremental and cooperative design in an orderly way. This calls for a version-control mechanism of some generality if it is to be appropriate to the design of complex objects. The authors consider the nature of design objects, and develop some functional requirements for version control of such objects. They outline the basic object-oriented database model, which they take as the foundation for their proposal. They then discuss the relationship between versions and the objects they exemplify, describe the mechanisms for the creation of versioned objects and the conversion of non-versioned objects to versioned form, study the impact on referencing and type checking in the object model, and arrive at a flexible notion of a context containing rules for version selection. Their implementation of some of these concepts is also described.<<ETX>>

A Foundation for Evolution from Relational to Object Databases

Object models have an important part to play in the future of database systems, but progress is hampered by lack of agreement on their essential characteristics. Strong constraints on the design of a common model are exercised by the need to interface well with object models in programming languages, and the desirability of a smooth evolution from existing database technology.

Intensional concepts in an object database model

There is a requirement for a stronger treatment of intentional concepts and more general inferential ability within database systems. A framework for achieving this will be described in terms of extensions to an object data model. The type Concept is introduced into the model as a subtype of Action. Intentional concepts may then be defined as filters or generators, depending on the nature of the defining formula. In either case, the dual action should be available—provided automatically by the system or explicitly by the user. Finally, sets and types are treated as special cases of extensional concepts, leading to a novel structure of the hierarchy of system types.

Concepts in user interfaces: a reference model for command and response languages

Overview of the reference model.- Application of the reference model.- Users.- Contexts.- Customisation.- Help.- History.- Concurrency.- CRL Object management.- Naming.- Protection.- Shared storage.

Criteria for a standard command language based on data abstraction

A solution is offered to some fundamental problems that have thwarted previous efforts to develop a standard command language. The technical approach is based on the form of modularity provided by data abstraction, and this is introduced from the point of view of the end user, together with a discussion of the advantages and disadvantages that might be perceived at this level. This leads to the statement of a simple but stringent set of criteria for the inclusion of functional capabilities in a standard command language and the testing of various candidates against them. Some candidates are accepted and others rejected, resulting in an initial proposal for the scope of a standard command language that is small and simple enough to have a hope of success.

Modularity in the design and standardisation of open systems

Abstract Some practical suggestions are made as to how data abstraction may be used to provide a modular framework for the design of open systems and their means of interconnection. This framework is technically advantageous in clarifying the interfaces between the parts of a large design, and would also help in planning and coordinating the work of standards committees. A reference model for languages applicable to local system function is compared with the reference model for open systems interconnection (OSI), and a clarification is suggested which would make the models compatible. Two major functional requirements are proposed for the application layer of the OSI model, namely the ability to transmit arbitrary operations to be performed on remote objects, and the option to specify whether objects or merely references to them should be transmitted.