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This paper describes the use of a persistent store to support incremental system construction. A single example is elaborated throughout the paper to introduce elements of the incremental construction mechanism. The essence of the technique is to permit assignment of executable program fragments to typed locations in order to change the behaviour of a program under construction. The technique described in this paper relies upon the existence of three features: a persistent store, updatable locations and first class executable values. The examples in this paper use the persistent programming language Napier88, but any language with these features could be used to construct such a system. 1. Introduction In many programming environments, the compilation units are syntactic entities which typically contain some data and a set of procedures (or functions) which provide access to that data. This approach is exemplified by packages in Ada [1] and Object Oriented Design Methodolog...

I hereby declare that I am the sole author of this thesis. This is a true copy of the thesis, including any required final revisions, as accepted by my examiners. I understand that my thesis may be made electronically available to the public. Components are widely seen by software engineers as an important technology to address the “software crisis”. An important aspect of components in other areas of engineering is that system reliability can be estimated from the reliability of the components. We show how commonly proposed methods of reliability estimation and composition for software are inadequate because of differences between the models and the actual software systems, and we show where the assumptions from system reliability theory cause difficulty when applied to software. This thesis provides an approach to reliability that makes it possible, if not currently plausible, to compose component reliabilities so as to accurately and safely determine system reliability. Firstly, we extend previous work on input sub-domains, or partitions, such that our