Software System Design and Implementation

Software Design and Implementation

• Software design and implementation is the stage in the software engineering process where an executable software system is developed.
• These activities are inter-leaved, meaning design informs implementation and vice versa.
• Software design is a creative activity that identifies software components and their relationships based on customer requirements.
• Implementation realizes the design as a program.

Process Stages

• There are various object-oriented design processes that depend on the organization using the process.
• Common activities in these processes include:
  • Defining the context and modes of use of the system
  • Designing the system architecture
  • Identifying principal system objects
  • Developing design models
  • Specifying object interfaces

System Context and Interactions

• Understanding the relationships between the software and its external environment is essential for deciding how to provide required system functionality and structure the system to communicate with its environment.
• Understanding the context also lets you establish the boundaries of the system, which helps decide what features to implement in the system and what features to implement in associated systems.

Context and Interaction Models

• A system context model is a structural model that demonstrates other systems in the environment of the system being developed.
• An interaction model is a dynamic model that shows how the system interacts with its environment as it is used.

Architectural Design

• Once interactions between the system and its environment are understood, this information is used to design the system architecture.
• The major components that make up the system and their interactions are identified, and components are organized using an architectural pattern such as a layered or client-server model.

Object Class Identification

• Identifying object classes is a difficult part of object-oriented design.
• There is no 'magic formula' for object identification, and it relies on the skill, experience, and domain knowledge of system designers.
• Object identification is an iterative process, and you are unlikely to get it right the first time.

Approaches to Identification

• Use a grammatical approach based on a natural language description of the system.
• Base identification on tangible things in the application domain.
• Use a behavioral approach and identify objects based on what participates in what behavior.
• Use a scenario-based analysis, where objects, attributes, and methods are identified in each scenario.

Design Models

• Design models show the objects and object classes and relationships between these entities.
• Static models describe the static structure of the system in terms of object classes and relationships.
• Dynamic models describe the dynamic interactions between objects.

Examples of Design Models

• Subsystem models show logical groupings of objects into coherent subsystems.
• Sequence models show the sequence of object interactions.
• State machine models show how individual objects change their state in response to events.

Design Patterns

• A design pattern is a way of reusing abstract knowledge about a problem and its solution.
• A pattern is a description of the problem and the essence of its solution.
• Patterns are useful for solving common problems in software design.

Implementation Issues

• Focus on other implementation issues that are often not covered in programming texts, such as:
  • Reuse: Most modern software is constructed by reusing existing components or systems.
  • Configuration management: managing changes to software systems.
  • Host-target development: developing software on one computer and executing it on another.

Reuse

• The abstraction level: reusing knowledge of successful abstractions.
• The object level: reusing objects from a library.
• The component level: reusing collections of objects and object classes.
• The system level: reusing entire application systems.

Configuration Management

• The process of managing a changing software system.
• Activities include version management, system integration, and problem tracking.

Host-Target Development

• Developing software on one computer and executing it on another.
• Development platform and execution platform may have different architectures and installed software.

Integrated Development Environments (IDEs)

• A set of software tools that supports different aspects of software development within a common framework and user interface.

Component/System Deployment Factors

• Factors to consider when deploying components or systems, such as hardware and software support, high availability, and communication traffic.

Open Source Development

• An approach to software development in which the source code of a software system is published and volunteers are invited to participate in the development process.
• Roots in the Free Software Foundation, which advocates that source code should not be proprietary.
• Open source software extended this idea by using the Internet to recruit a larger population of volunteer developers.