Open Source Development Principles

Chapter 7 - Design and Implementation

• Software design and implementation is the stage in the software engineering process where an executable software system is developed.
• Design and implementation activities are typically interwoven.
• Software design is a creative process identifying software components and their relationships based on customer requirements.
• Implementation is the process of translating the design into a program.
• Off-the-shelf systems (COTS) are available in many domains, allowing tailoring to meet user needs.
• Using COTS can be faster and cheaper than developing a system from scratch.
• The design process for COTS applications focuses on using configuration features to achieve system requirements.
• Object-oriented design processes involve creating various system models.
• These models require significant development and maintenance effort, making them less cost-effective for small systems.
• For large systems developed by multiple groups, design models are important communication tools.

Process Stages

• Various object-oriented design processes exist, influenced by the organization using them.
• Common activities include defining the system context and use modes, designing the system architecture, identifying principal system objects, developing design models, and specifying object interfaces.

Context and Interaction Models

• A system context model is a structural representation of other systems within the environment of the system being developed.
• An interaction model depicts how the system interacts with its environment during use.

Architectural Design

• Once interactions between the system and its environment are understood, the system architecture can be designed.
• Identifying major system components and their interactions, and using architectural patterns (e.g., layered, client-server) is part of this process.

High-Level Architecture of the Weather Station

• Architecture is presented as a diagram showing subsystems like fault manager, configuration manager, power manager, communication link, communications, data collection, and instruments.

Object Class Identification

• Identifying object classes is a challenging aspect of object-oriented design.
• There's no single formula; it relies on domain expertise and experience of the designers.
• Identifying objects often involves an iterative process.

Design Models

• Design models illustrate objects, classes, and relationships.
• Two types of models exist:
  • Structural models depict the static system structure using classes and relationships.
  • Dynamic models describe the dynamic interactions between objects.

Examples of Design Models

• Subsystem models group objects into logical subsystems (packages).
• Sequence models show the order of object interactions.
• State machine models demonstrate how individual objects change state in response to events.
• Other models, such as use-case models, aggregation models, and generalization models, also exist.

Design Patterns

• Design patterns are methods for reusing abstract knowledge about problems and their solutions.
• Patterns document the problem, solution, and essence of the approach.
• Patterns should be abstract enough to be reused in diverse situations.
• Patterns commonly utilize object-oriented characteristics like inheritance and polymorphism.

Pattern Elements

• Name identifies the pattern.
• Problem description defines the problem solved by the pattern.
• Solution description outlines the solution approach.
• Consequences detail the results and trade-offs of applying the pattern.

Implementation Issues

• Implementation focuses on issues beyond programming, including:
  • Reuse of existing components or systems.
  • Configuration management for tracking software component versions.
  • Host-target development where the development environment and execution environment are different.

Open Source Development

• Open source development makes source code publicly available for community contributions and modifications.
• This approach is rooted in the Free Software Foundation, which advocates for publicly accessible source code.

Open Source Systems

• The Linux operating system is a prominent example of an open source product.
• Other open source products include Java, Apache web server, and MySQL.

Open Source Business

• Various product companies use open-source approaches for development.
• They believe this approach allows for cheaper, faster development and creation of a strong user community.

Open Source Licensing

• Although open source code is freely available, developers still own the code; thus, license conditions for its use are important.
• Some developers believe that systems using open-source components should also be open source.
• Some developers allow their code for use without restrictions.

Key Points

• Software design and implementation are intertwined.
• Object-oriented design includes designing the system architecture, identifying objects, relating objects using models, and documenting interfaces.
• Object-oriented design often produces diverse models.
• When developing software, consider reusing existing components, services, or complete systems.
• Open source development involves making source code public.

This quiz explores essential concepts of open source development, including its principles, benefits, and the role of community involvement. It also touches on object-oriented design and the structure of design patterns. Test your knowledge on these key areas and see how well you understand the fundamentals of software development.