A Coordination Perspective on Software Architecture: Towards a Design Handbook for Integrating Software Components

This thesis argues that many of the difficulties associated with building software applications by integrating existing components are related to a failure of current programming languages to recognize component interconnection as a separate design problem, orthogonal to the specification and implementation of a component's core function. It proposes SYNOPSIS, an architectural description language which supports two orthogonal abstractions: activities, for representing the functional pieces of an application, and dependencies, for describing their interconnection relationships. Coordination processes, defined as an attribute of dependencies, describe implementations of interconnection protocols. Executable systems can be generated from SYNOPSIS descriptions by successively replacing activities with more specialized versions and managing dependencies with coordination processes, until all elements of the description are specific enough for code generation to take place. Furthermore, it proposes a "design handbook", consisting of a vocabulary of common dependency types and a design space of associated coordination processes. The handbook is based on the insight that many software interconnection relationships can be described using a relatively narrow set of concepts orthogonal to the problem domain of most applications, such as resource flows, resource sharing, and timing dependencies. A prototype component-based application development tool called SYNTHESIS was developed. SYNTHESIS maintains a repository of increasingly specialized dependency types, based on the proposed design handbook. It assists the generation of executable applications by successive semi-automatic transformations of their SYNOPSIS descriptions. A set of four experiments is described. Each experiment consisted in specifying a test application as a SYNOPSIS diagram, associating application activities with components exhibiting various mismatches, and using SYNTHESIS to assemble these components into executable systems. SYNTHESIS was able to exploit its dependencies repository in order to resolve a wide range of interoperability and architectural mismatches and integrate independently developed components into the test applications, with minimal or no need for additional manually-written code. It was able to reuse a single SYNOPSIS architectural description in order to generate versions of a test application for two different execution environments. Finally, it was able to suggest various alternative architectures for integrating each component set into its corresponding application.