Benefits and problems of reuse; reuse planning

Software reuse means building new systems from existing software assets (components, designs, whole applications) instead of developing everything from scratch.

Benefits of software reuse

1. Increased dependability – reused software has been tried and tested in working systems, so its faults are already found and fixed.
2. Reduced process risk – the cost of existing software is known, so cost and schedule estimates are more accurate.
3. Effective use of specialists – experts build reusable components once instead of repeating the same work in many projects.
4. Standards compliance – standard components (e.g. a common UI library) make all applications look and behave consistently.
5. Accelerated development – less new code means faster delivery and lower cost.

Problems of software reuse

1. Increased maintenance costs – if the source code of a reused component is not available, maintenance becomes harder as the system changes.
2. Lack of tool support – CASE tools may not support development with reuse.
3. Not-invented-here syndrome – engineers prefer to rewrite components, believing they can do better.
4. Creating and maintaining a component library – building a well-catalogued library and keeping it up to date is expensive.
5. Finding, understanding and adapting components – engineers must be confident a component is correct and fits before using it.

Factors in reuse planning

1. Development schedule – a tight schedule favours reusing COTS systems or large components.
2. Expected software lifetime – long-life systems need maintainability, so access to source code becomes important.
3. Background, skills and experience of the team – reuse technologies (frameworks, generators) need specialised skills.
4. Criticality and non-functional requirements – safety-critical systems may need certified components and full source code; strict performance needs may rule out generated code.
5. Application domain – some domains (e.g. ERP, banking) have ready-made product lines and frameworks.
6. Execution platform – components must be compatible with the target hardware, OS and middleware.
7. Cost of buying, adapting and integrating components versus building new ones.