1. Architectural Design

2. Objectives • To discuss the relationships between architectural design and product and detailed design • To list influences on architectural design • To review the architectural design process • To present the contents of a software architecture document (SAD) • To explain quality attributes and their role in architectural design • To survey architectural specification notations, especially those for interfaces

3. Topics • Architectural design, product design, and detailed design • Architectural design influences • The architectural design process • Quality attributes • Architectural design specifications

4. Architectural Design Architectural design is the activity of specifying a program’s major parts; their responsibilities, properties, and interfaces; and the relationships and interactions among them.

5. Architectural Design During Product Design Architecture is often needed during product design to • Judge feasibility • Convince stakeholders their needs can be met • Conduct tradeoff analyses • Plan the project

6. Architectural versus Detailed Design Often the distinction between architectural and detailed design is not clear. • What is a “major” program part? • How abstract should architectural specifications be? • What is the architecture of a very small program?

7. Influence on Architectural Design • Code libraries and other assets • Organizational structure • Knowledge and experience of designers • Architectures influence people and organizations too

8. Architectural Design Process

9. Software Architecture Document (SAD) Contents • ProductOverview—Product vision, stakeholders, target market, etc. • ArchitecturalModels—Specification using various models, both static and dynamic • DeSCRIPTR • Mapping BetweenModels—Tables and text relating models • Architectural DesignRationale—Explanation of difficult, crucial, puzzling, and hard-to-change design decisions

10. Quality Attributes A quality attribute is a characteristic or property of a software product independent of its function that is important in satisfying stakeholder needs. • Non-functional requirements • Architectures have a big influence on quality attributes • Development or operational attributes • Techniques for using quality attributes (later)

11. Development Attributes • Maintainability—Ease with which a product can be corrected, improved, or ported • Often subdivided • Reusability—Degree to which a product’s parts can be reused in another product • Others

12. Operational Attributes • Performance—Ability to accomplish product functions within time or resource limits • Availability—Readiness for use • Reliability—Ability to behave in accord with requirements under normal operating conditions • Security—Ability to resist being harmed or causing harm by hostile acts or influences • Others

13. Notations for Architectural Specifications

14. Interfaces An interface is a communications boundary between entities. An interface specification describes the mechanism that an entity uses to communicate with its environment.

15. Interface Specifications • Syntax—Elements of the communications medium and how they are combined to form messages • Semantics—The meanings of messages • Pragmatics—How messages are used in context to accomplish tasks • Interface specifications should cover the syntax, semantics, and pragmatics of the communication between a module and its environment.

16. Interface Specification Template

17. Semantic Specification • A precondition is an assertion that must be true at the start of an activity or operation. • A postcondition is an assertion that must be true at the completion of an activity or operation. • Pre- and postconditions can together specify what happens when an operation executes, thus explaining its semantics.

18. Summary 1 • Architectural design must usually begin during product design to help product feasibility. • Architectural design may shade into detailed design. • A SAD contains an overview, architecture specifications, and design rationale. • Architectural decisions greatly influence quality attributes.

19. Summary 2 • A variety of notations are used for architectural modeling. • Interface specifications should include descriptions of a communication medium’s • Syntax, • Semantics, and • Pragmatics.