Software productivity has been steadily increasing over the last 30 years, but not enough to close the gap between the demands placed on the software industry and what the state of the practice can deliver [22,39]; nothing short of an order of magnitude increase in productivity will extricate the software industry from its perennial crisis [39,67]. Several decades of intensive research in software engineering and artificial intelligence left few alternatives but sofware reuse as the (only) realistic approach to bring about the gains of productivity and quality that the software industry needs. In this paper, we discuss the implications of reuse on the production, with an emphasis on the technical challenges. Software reuse involves building software that is reusable by design, and building with reusable software. Software reuse includes reusing both the products of previous software projects, and the processes deployed to produce them, leading to a wide spectrum of reuse approaches, from the building blocks (reusing products) approach on one hand, to the generative or reusable processor (reusing processes) on the other [68]. We discuss the implications of such appproaches on the organization, control, and method of software development and discuss proposed models for their economic analysis. Software reuse benefits from methodologies and tools to: 1) build more readily reusable software, and 2) locate, evaluate, and tailor reusable software, the latter being critical for the building blocks approach. Both sets of issues are discussed in this paper, with a focus on application generators and object-oriented development for the first, and a thorough discussion of retrieval techniques for software components, component composition (or bottom-up design) and transformational systems for the second. We conclude by highlighting areas that, in our opinion, are worthy of further investigation.

A safety case should present a clear, comprehensive and defensible argument that a system is acceptably safe to operate within a particular context. However, many existing safety cases, in their attempt to manage potentially complex arguments, are poorly structured, presented and understood. This creates problems in developing and maintaining safety cases, and in capturing successful safety arguments for use on future projects. This thesis defines and demonstrates a coherent approach to the development, presentation, maintenance and reuse of the safety arguments within a safety case. This approach is based upon a graphical technique -- the Goal Structuring Notation (GSN) -- and has three strands. Firstly, a method for the use of GSN is defined together with an approach to supporting incremental safety case development. Secondly, the thesis presents a systematic process for the maintenance of a GSN-structured safety argument. Thirdly, the concept of `Safety Case Patterns' is defined as a means of supporting and promoting the reuse of successful safety arguments between safety cases. Examples of the approach are provided throughout. Evaluation of the approach is described through tool implementation, case studies, pilot projects and industrial project applications. Through these activities the approach has been shown to be both a valid and capable tool for safety case management.

In this paper we investigate the impact of human cogni-tion on developers ability to effectively reuse software artefacts. We look at the cognitive impediments to and furtherance of software reuse. We review the computing models of human knowledge and reasoning which may assist in the emulation of our abilities to reuse software. Finally we investigate the possibility of integrating human and machine capabilities to arrive at the efficient method of software reuse.