Software Design: Principles, Process, and Concepts

1
Software Design Principles, Process, and Concepts

• Getting Started with Design

2
General Information on Design

• Analysis (requirements) model vs. design model
• End User vs. Developer
• Function and behavior (what) vs. architecture,
  interface, and component (how)
• Primary views of the design
• Data/Classes necessary information, data
  structures, data stores, objects and actors
• Architecture Overall big picture of
  relationships among system elements, design
  framework and patterns
• Deployment How system is hosted in target
  environment (i.e., what computers, data files,
  networks, and/or other infrastructure).
• Interfaces user, external, and internal
• Components refinement of visible object classes
  to include system, support, and utility classes.

3
Design Modeling Principles

• Design should result from analysis
• Design should consider s/w architecture first
• Give thought to data structures (foundation of
  design). Good data design simplifies components.
• Give extra care to communicate across interfaces
• Keep user in mind when creating UI, stress easy
  use, not easy implementation.
• Keep components cohesive (functionally
  independent)
• Keep components loosely coupled (simple
  interfaces)
• Keep your designs (and design descriptions)
  simple and easily understood
• Develop the design iteratively
• See task set on pg 112 6/e (and more detailed on
  pg 222 7/e, pg 232 6/e)

4
Design Modeling Process

• Class Modeling
• Examine analysis class diagrams for data
  characteristics content, pervasiveness,
  sharing, flow, transformation, persistence
• Examine analysis class diagrams and use cases for
  problem domain actors and objects, processes,
  constraints, and interfaces
• Architecture Modeling
• Identify all major system components
• Determine relationships among major components,
  business processes, system elements
• Apply design framework or pattern (if
  appropriate)
• Interface Design
• Three interface types user, external and
  internal
• Component-Level Design
• Elaborate and refine detail of major components
• Add helper, system and utility classes as
  required
• Re-factor as required

5
Design Modeling Concepts

• Abstraction allows us to handle complexity
• Architecture organizes program components
• Patterns when applicable, provides insight or
  guidance for design choices
• Modularity the mechanism for implementing
  abstractions
• Information Hiding inhibits side effect errors
• Functional Independence low coupling and high
  cohesion
• Refinement the manner in which designs are
  elaborated
• Refactoring improving the internal structure of
  the design or code

6
Additional Points of Emphasis

• Diversification and convergence (pg 216 7/e,
  pg227 6/e)
• Quality Attributes (pgs 220-221 7/e, pgs 231-232
  6/e)
• Functionality
• Usability
• Reliability
• Performance
• Supportability
• Design Classes (pg 230 7/e, pg 239 6/e)
• UI Classes
• Business Domain Classes
• Process Classes
• Persistent Classes
• System Classes

Application-specific classes