Architectural styles are named collections of constraints on configurations of architectural elements, and are believed to bring economies of scale in applying software architecture techniques to software development. Existing research on architectural styles provides little guidance for the systematic design and construction of architectural style elements. This paper proposes a framework, Alfa, for systematically and constructively composing "architectural primitives" to obtain elements of architectural styles. This is based on our observation that architectural styles share many underlying concepts that lead to architectural primitives. We have identified eight forms and nine functions as architectural primitives that reflect the syntactic and semantic characteristics of architectural styles and are expressive enough to compose their elements. Our approach is also illustrated using a familiar style -- pipe-and-filter.

Software systems of today are frequently composed from prefabricated, heterogeneous components that provide complex functionality and engage in complex interactions. Existing research on component-based development has mostly focused on component structure, interfaces, and functionality. Recently, software architecture has emerged as an area that also places significant importance on component interactions, embodied in the notion of software connectors. However, the current level of understanding and support for connectors has been insufficient. This has resulted in their inconsistent treatment and a notable lack of understanding of what the fundamental building blocks of software interaction are and how they can be composed into more complex interactions. This paper attempts to address this problem. It presents a comprehensive classification framework and taxonomy of software connectors. The taxonomy is obtained through an extensive analysis of existing component interactions. The taxonomy is used both to understand existing software connectors and to suggest new, unprecedented connectors. We demonstrate the use of the taxonomy on the architecture of a large, existing system.