The History of Software Architecture 1

1
The History of Software Architecture (1)

• INFO3011 Software Architecture and Design
• downloadable pdf file

2
Leading Contributors

• The leading contributors of the modern discipline
  of Software Architecture to date are
• Dewayne Perry and Alexander Wolf
• Mary Shaw and David Garlan
• Len Bass, Paul Clements, Rick Kazman and Linda
  Northrup
• Frank Buschmann et al.,
• James O. Coplien

3
Foundations of Study

• The seminal work is a 1992 paper by Dewayne E.
  Perry and Alexander L. Wolf
• Foundations for the Study of Software
  Architecture. ACM SIGSOFT Software Engineering
  Notes 17(4) pp.40-52
• Constructed a model of Software Architecture
  consisting of 3 components
• Elements
• Form
• Rationale

4
Perry and Wolf, 1992

• We use the term architecture rather than
  design to evoke notions of codification, of
  abstraction, of formal training (of software
  architects), and of style
• Benefits sought
• Architecture as a framework for satisfying
  requirements
• Architecture as the technical basis for design
• Architecture as an effective basis for reuse
• Architecture as the basis for dependency and
  consistency analysis

5
Basis of the Intuition

• Perry and Wolf examined other architectural
  disciplines for lessons
• Computing hardware architecture
• Small number of design features
• Scale achieved by replication of the design
  elements
• Network architecture
• Two kinds of components nodes and connections
• Only a few topologies to be considered
• Building architecture
• Multiple views
• Architectural styles
• Style and engineering
• Style and materials

6
The Context of Architecture

• Requirements are concerned with the determination
  of the information, processing and
  characteristics of that information needed by the
  user of the system
• Architecture is concerned with the selection of
  architectural elements, their interactions, and
  the constraints on those elements and their
  interactions necessary to provide a framework in
  which to satisfy the requirements and serve as a
  basis for design
• Design is concerned with the modularisation and
  detailed interfaces of the design elements, their
  algorithms and procedures, and the data types
  needed to support the architecture and to satisfy
  the requirements and
• Implementation is concerned with the
  representations of the algorithms and data types
  that satisfy the design, architecture and
  requirements.

7
The Purpose of Architectural Specification

• Architectural specifications are required to be
  of such a character that we can
• Prescribe the architectural constraints to the
  desired level
• Separate aesthetics from engineering
• Express different aspects of architecture in an
  appropriate manner
• Perform dependency and consistency analysis

8
The Model elements

• Software Architecture elements, form,
  rationale
• Elements
• Processing elements
• Data elements
• Connecting elements

9
The Model form

• Form
• Consists of weighted properties and relationships
• Weighting is either
• Importance of property or relationship
• Or necessity of selecting among alternatives
• Properties
• Define the minimum constraints on the choice of
  architectural elements
• Relationships
• used to constrain the placement of
  architectural elements and how they interact

10
The Model rationale

• Rationale
• Is underlying, but integral
• Captures the motivation for the choice of style,
  elements and form
• In building architecture
• Rationale explicates underlying philosophical
  aesthetics
• In software architecture
• Instead explicates the satisfaction of system
  constraints
• Functional and non-functional

11
Architectural Style

• Perry and Wolf noted that, distinct from other
  architectural disciplines, software architecture
  had no named styles
• They proposed that architectural styles be used
  as constraints on an architecture
• The important thing about an architectural style
  is that it encapsulates important decisions about
  the architectural elements and emphasizes
  important constraints on their elements and their
  relationships