Presented by Charles Reid 2/7/2005 Foundations for the Study of Software Architecture by Dewayne Perry & Alexander Wolf ACM SIGSOFT, Oct. 1992 Presented by Charles Reid 2/7/2005

Dewayne E. Perry Undergrad degree in Philosophy with a M.S. and Ph.D. in Computer Science Long list of academic employment including UCLA (philosophy), CMU, and University of Texas at Austin Tons of professional research on software processes and software engineering Board member of International Software Process Association (ISPA).

Alexander L. Wolf Prof. of Computer Science at the University of Colorado at Boulder Director of Software Engineering Research Lab Chair of the ACM Special Interest Group in Software Engineering (SIGSOFT) Several publications in several areas – Networking, Distributed Systems, Software Architecture, Software Process, Security, Component Management, …

Purpose of the Paper The purpose is “to build the foundation for software architecture”. They look at other architectural disciplines to gain an intuition for software architecture. The paper proposes a model for software architecture and provides an example

Where Does Architecture Fit? Requirements Determine what information, processing, and characteristics of the information processing are needed Architecture Determines architectural elements, their interactions, and the constraints they are subject to Design Modularization and detailed interfaces, algorithms, and data types to support the architecture Implementation Representations of elements from the design

Why are they doing this? The authors expect that disciplined software architecture will: Provide an architectural framework for satisfying requirements Provide a basis for design, cost estimation, and process management Promote reuse Provide a basis for consistency and dependency analysis Provide a way to separate aesthetics from engineering

Architectural Erosion and Drift The system becomes more brittle due to violations of the original architecture Architectural Drift Due to “insensitivity about the architecture” They claim this leads to inadaptability which can lead to lack of clarity or coherence Erosion – sequential processing and then someone introduces concurrency somewhere which makes the system more susceptible to problems

Gaining the Intuition for Software Architecture Computer Architecture Not a useful basis for software architecture due to fundamental differences Relatively small number of design elements and scale is achieved through replication Network Architecture Also not too useful Focuses on nodes and connections and deals with a small number of topologies Relatively small number of design elements in hardware and

Gaining the Intuition for Software Architecture Building Architecture Provides useful insight Multiple views of same structure Architectural styles Style and engineering Style and materials Styles are descriptive and prescriptive, constrains elements and the formal relationships between them Can be applied to software systems, distributed might be a style, message passing

The Architectural Model Software Architecture = {Elements, Form, Rationale} Elements can be processing elements, data elements, or connecting elements Form consists of weighted properties and relationships Weighting indicates importance or necessity of the relationship Rationale is the reasoning behind the architectural decisions Water polo metaphor, players = processing elements, ball = data element, water = connecting element

Compiler Example Compiler with 5 phases Processing elements = {lexer, parser, semantor, optimizer, code generator} Data elements = {characters, tokens, phrases, annotated phrases, object code} Connecting Elements = {procedure calls, parameters}

Compiler Example cont. Form might dictate that the optimizer and annotated phrases must accompany each other but they are not necessary elements Form might also dictate relationship between data elements

Processing Architectural View Shows flow of data, relationships between processing elements

Architectural Data View Uses application-oriented properties to show the state of data that are important to the processing elements that manipulate the data

Comparing Different Compiler Models

Conclusions They believe that they’re model and the use of application-oriented properties will: Make it easier to compare architectures Make it easier to determine which architectural components can be reused Better illustrate the dependencies and consistency between architectural elements