摘要:

This paper describes the design and implementation of a distributed file system (dfs) for embedded applications. The services provided in dfs include transaction management, file management and file access. Client processes use message passing to access these services. The file system provides client processes with different types of files. These includereplicatedfiles, with identical copies stored at multiple nodes, andconsistentfiles, stored at a single node. Both are accessed only within transactions. Multiple readers or a single writer are allowed access to the files, and updates are performed atomically using a co-ordinated commit protocol over multiple sites. A novel concurrency control algorithm which provides deterministic response and avoids deadlock has been designed to resolve contention. Other types of file are also provided for low-overhead storage of less critical data. This paper motivates the need for different types of file, and describes the design and implementation of dfs using the CONIC programming environment for the construction of distributed systems.

DOI:10.1049/sej.1988.0017

出版商:IEE    

年代:1988

数据来源: IET

摘要:

Unification is an important concept. It is used in Prolog, resolution, term rewriting and natural language understanding. As the use of formal methods increases, unification will be part of formally developed systems. Hence a theory of unification is desirable. This paper demonstrates the use of VDM to develop a theory of unification. Substitution application is defined recursively, a theory of non-circular substitutions is developed, and an implicit specification of unification is written. A proof of a particular unification algorithm is outlined with respect to this specification. The algorithm considered is more space-efficient than that which Manna and Waldinger prove correct. The theory developed is also compared with that of Manna and Waldinger.

DOI:10.1049/sej.1988.0018

出版商:IEE    

年代:1988

数据来源: IET

摘要:

Advances in communications technology allow the construction of very large distributed computing systems (VLDCSs) containing thousands of computers and spanning several organisational boundaries. Existing management tools and approaches are not appropriate to the size and multiple-organisation nature of these VLDCSs. This paper describes a new approach to the management of VLDCSs based on a domain model. While this model is applicable to most aspects of management, the paper describes an implementation of the domain model for management of access rights. Domains provide a flexible means for specifying access control policies, which reflect organisational structure, and permit secure inter-organisation interactions, while giving users transparent access to resources. The paper describes an implementation of domains in terms of capability-based access rights, which meets the flexibility and security requirements for managing VLDCSs. Security is enhanced by physically preventing programs from directly accessing capabilities.

DOI:10.1049/sej.1988.0019

出版商:IEE    

年代:1988

数据来源: IET

摘要:

This paper discusses the practical problems associated with the widespread implementation of re-usable software. The problems raised are not solely technical in nature, some being rooted in the cultural environment of current procurement, commercial and software engineering practices. The paper concludes that there needs to be a concerted effort by customers, suppliers and educational establishments in order to encourage software re-use to take off.

DOI:10.1049/sej.1988.0021

出版商:IEE    

年代:1988

数据来源: IET

摘要:

The development of the Ada language precipitated a number of studies of Ada software re-use. This paper presents some of the authors' conclusions from such studies, with references to the available Ada literature.

DOI:10.1049/sej.1988.0022

出版商:IEE    

年代:1988

数据来源: IET

摘要:

This paper presents the work of the TARA (Tool Assisted Requirements Analysis) project on the re-use of formatted specifications. The paper concentrates particularly on the established formatted requirements analysis method CORE (Controlled Requirements Expression). A model of re-use of formatted requirements specifications, derived in part from studies of analogy in legal reasoning, is presented. The model and its application to CORE is described in detail with a worked example based on standard specification case studies. A prototype tool, TRUE, constructed on the basis of the model is described.

DOI:10.1049/sej.1988.0024

出版商:IEE    

年代:1988

数据来源: IET

摘要:

This paper describes an information retrieval system which is specifically designed to be used for storing and retrieving information about software components. Rather than use a retrieval mechanism which is simply based on keyword descriptions, the authors have made use of developments in natural language research to represent component information in a form which encodes semantics as well as syntax. The authors call this the component descriptor frame. The paper describes the basic ideas which underlie the system and describes how they can be used for component information retrieval. An example of the system in use is presented. The version of the system described here has been fully implemented using Prolog and is now being developed as part of a more general re-use support system.

DOI:10.1049/sej.1988.0025

出版商:IEE    

年代:1988

数据来源: IET

摘要:

A problem domain analysis is described employing a method recently developed and applied at the Warton Unit of the Military Aircraft Division of British Aerospace. The method is based on the definition of attributes of a software component which categorise the component as re-usable, re-usable with modification or non-re-usable. These attributes were presented to a domain specialist in the form of a structured questionnaire. This work is the first stage in discovering ways to design a re-usable software component. Also detailed are the stages involved in the re-design of one of the re-usable components to enhance its re-usability, and an evaluation of the University of Strathclyde's intelligent knowledge-based cataloguing system is given. Finally, further work towards the development of a re-use support system is summarised.

DOI:10.1049/sej.1988.0026

出版商:IEE    

年代:1988

数据来源: IET