Software Reuse and Configuration Management

Implementation Issues

• Focus is on implementation issues beyond programming, a crucial but often overlooked aspect.

• Reuse: Modern software is often constructed by reusing existing components or systems. Maximize use of existing code for development.

• Configuration Management: Throughout development, track various versions of each software component using config management systems.

• Host-Target Development: Production software often executes on a different computer than the development environment. Develop on a "host" and execute on a "target" machine.

Reuse

• From the 1960s to the 1990s, most software was developed from scratch using high-level programming languages.
• Reuse mainly involved functions and objects in programming language libraries..
• Cost and schedule pressures made the purely "from-scratch" approach increasingly impractical, especially for commercial and web-based systems.
• An approach for development relying on existing software emerged and is now common for business and scientific software.

Reuse Levels

• Abstraction Level: Reuse knowledge of successful abstractions in design, not the software directly.

• Object Level: Reuse objects directly from libraries instead of writing code yourself.

• Component Level: Reuse components which are collections of objects and object classes within application systems.

• System Level: Reuse entire application systems.

Software Reuse

• System (Application Systems (COTS)): Top level of software reuse.

• Abstraction (Architectural and Design Patterns): Lowest level of software reuse.

• Component (Component Frameworks): Mid level of software reuse.

• Object (Programming Language Libraries): Mid level of software reuse.

Reuse Costs

• Time spent locating and assessing reusable software.

• Costs of purchasing the reusable software especially for off-the-shelf systems.

• Costs of adapting and configuring the reusable software to match project needs.

• Costs of integrating reusable software components from different sources with new codebase.

Configuration Management

• Configuration management (CM) is the general term for managing changes in a software system.
• CM ensures all project code and documentation is accessible in a controlled method.
• CM tracks changes and manages compiling and linking of components to create a system.
• Refer to Chapter 25 for more detail.

Configuration Management Activities

• Version management: Tracking different versions of software components. Version management systems are used to coordinate development by developers.

• System integration: Defining component versions to build a system. Used to build the system automatically by compiling and linking components.

• Problem tracking: Reporting and managing bugs and other issues. Developers can see who is working on issues and when they are fixed.

Configuration Management Tool Interaction

• Diagrams illustrate the interaction between various configuration management tools.

Host-Target Development

• Most software is developed on one machine (the host) and runs on a different machine (the target).

• This means more than just hardware, it deals with the development platform (e.g., IDE, compilers, testing tools) and the execution platform (e.g., libraries, related systems, databases.)

• The development platform often has different software and architectures from the execution platform.

Development Platform Tools

• Integrated compiler & syntax-directed editor: Creating, editing, and compiling code.

• Language debugging system: Debugging support.

• Graphical editing tools (e.g., for UML models): Visual modeling tools.

• Testing tools (e.g., JUnit): Automating test execution.

• Project support tools: Organizing the codebase for different project phases.

Integrated Development Environments (IDEs)

• IDEs group development tools to create a coherent environment for software development.

• IDEs provide common framework and user interface for various development tasks (e.g., coding, compiling, testing).

• Software tools often created to support a specific language, e.g. Java.

Component/System Deployment Factors

• Components designed for specific architectures need to be deployed onto platforms supporting them.

• High-availability systems may need deployment on multiple platforms to ensure continued operation during failure.

• Frequent communication between components is better served on the same or nearby platforms to reduce communication latency.

Open Source Development

• Open source development involves publishing the source code of a software system and inviting volunteers to contribute to the development process.

• The Free Software Foundation (FSF) advocates for free availability of source code and not proprietary software.

• Open source software allows the use of the internet to recruit large populations of volunteer developers.

Open Source Systems

• Linux is the most prominent open-source operating system, used as a server and increasingly as a desktop environment.

• Other prominent open-source products include Java, Apache web server, and MySQL database management system.

Open Source Issues

• Should existing products use open source components?

• Should an open source approach be applied to development ?

Open Source Business

• More companies adopt open-source approaches for software development.

• Businesses focus on selling support for open-source products rather than the products themselves.

• Involvement of open-source communities is viewed as enhancing product development in terms of speed, cost, and user base.

Open Source Licensing

• Open source development embraces accessible source code but does impose legal restrictions (e.g., license requirements).

• Developers retain ownership of their code.

• Open source licenses can restrict usage and define how the code can be used legally.

• Some favor open-source components for developed systems while others allow proprietary systems.

License Models

• GNU General Public License (GPL): Reciprocal license; if you use GPL software, you must make the software open source.

• GNU Lesser General Public License (LGPL): Variant of GPL; permite linking to open source code without having publish the source of these components.

• Berkeley Standard Distribution (BSD) License: Non-reciprocal; you are not obliged to re-publish any changes to the open source code, you can use it in proprietary systems.

License Management

• Maintain information about open-source components.
• Be aware of open-source license types and terms.
• Understand component licensing before use.
• Be aware of evolution pathways for components.
• Educate development team about open-source issues.
• Auditing systems should be in place.
• Active participation in open-source communities.

Key Points (Software Design and Implementation)

• Software design and implementation intertwine directly, and details depend on specific system type (plan-driven vs agile)
• The object-oriented design process involves steps for designing system architecture, identifying objects in systems, describing designs with models, and documenting component interfaces.
• Different models (static, dynamic) aid in object-oriented design process.
• Component interfaces need precise definition for use by other objects (e.g., UML interfaces).

Key Points (General)

• Reuse consideration is important during software development (components, services, or complete systems).
• Configuration management is essential for maintaining consistency in evolving systems, especially when multiple developers are collaborating.
• Most software development now follows the host-target model (development on one computer, execution on another).
• Open-source development involves making source code public, encouraging broader participation and improvements.