Software Architecture

Introduction to Software Architecture

• Software architecture encompasses the set of significant decisions about the organization of a software system :
  • Selection of structural elements and their interfaces by which a system is composed.
  • Behaviour as specified in collaborations among those elements.
  • Composition of these structural and behavioural elements into larger subsystem.
  • Architectural style that guides this organization.

• Definition:
  • The structure or structures of the system which comprise of software elements, the externally visible properties of those elements and the relationships among them.

Why Architecture

Communication

• There are different stakeholders (client, user, project manager, developer, maintainer) who want different qualities of the system being built.
• E.g. client is concerned about cost, user about usability, project manager about dividing work, developer about implementation and maintainer about making changes.
• An architecture provides a framework and structure for airing these concerns.

Capture early design decisions

• An architecture constrains implementation.
• An architecture can help to determine organisational structure.
• Allow apriori reasoning about change.
  • Probably the most important - since 80% of software cost occurs after deployment.
  • Enables risk assessment of future project changes.
• Support analysis and prediction about future properties.

Reusable abstraction of systems

• The earlier a software artefact can be reused, greater the payoff.
• Architectural reuse - means not only reuse code, but also requirements and development experience.
• Domain specific software architectures can be developed.
• Process becomes oriented towards component assembly rather than programming.

Problems due to lack of architecture

• Costly maintenance - prone to side effect problems.
• Evolution not possible and reuse difficult.
• Inefficient or infeasible
  • Arch may partition the work in such a way that every engineer must communicate with every other engineer.
  • Throughput problems - processing bottlenecks, etc.

Influences on architecture

• Software architecture is a result of technical, business and social influences.
• System stakeholders.
• Developing organisation.
  • Org may have a business investment in certain assets.
  • May wish to make a long term business investment.
  • The organizational structure can shape the software architecture.
• Background and experience of architects.
• Technical environment.