Reusing and Interconnecting Software Components

This article covers some problems, concepts, and approaches relevant to environments for creating, documenting, and maintaining large software systems. The goal is to make programming significantly easier, more reliable, and cost effective by reusing previous code and programming experience to the greatest extent possible. Suggestions given here include: systematic (but limited) use of semantics, by explicitly attaching theories (which give semantics, either formal or informal) to software components with views (which describe semantically correct interconnections at component interfaces); use of generic entities, to maximize reusability; a distinction between horizontal and vertical composition; use of a library interconnection language, called LIL, to assemble large programs from existing entities; support for different levels of formality in both documentation and validation; and facilitation of program understanding by animating abstract data types and module interfaces. ADA is used for examples because it has some convenient features, but the proposals also apply to other languages.