Introduction Software is becoming very expensive: a possible way to reduce cost: reuse parts from previously made software. assemble software from off-the-shelf components.
Introduction Advantages of reuse also include: reduced number of defects: standard and well-tested components are reused. reduced development time: provide early market access for products.
Software reuse Software development with reuse: similar to an electronic engineer building an electronic circuit: uses standard types of electronic ICs and other components.
At the most abstract level: What can be reused? Specification Design Code Test cases At the most abstract level: knowledge
Reuse of Knowledge More difficult compared to day- to-day reuse of knowledge: developers vary over time and over projects difficult to remember details of potentially reusable development knowledge.
Why almost no software reuse so far? Engineers working in industry often have a frustrated feeling: current system is similar to last few systems they have already built everything is being built from scratch current system is behind schedule: no one has time to figure out what this similarity really means.
Another complaint In spite of having software components available for reuse: programmers have preferred to create their own, because: available components are difficult to understand difficult to adapt to new application
Basic Issues in Software Reuse Component creation Component indexing Search Understanding Adaptation Repository maintenance
Basic Issues Component creation: Component indexing: Identify reusable components Component indexing: classification of reusable components so that they can be easily searched when we look for a component to reuse.
Basic Issues Search: search for right components in a database of components requires a proper method to describe components
Basic Issues Understanding: to decide whether we can use some component we need a precise and sufficiently complete understanding of what the component does.
Basic Issues Adaptation: A selected component may not exactly fit the problem at hand Tinkering with the code is not satisfactory: in any case justified only if thoroughly understood
Basic Issues Repository maintenance: component entering tracking faulty components new applications emerge older applications become obsolete components might need changes obsolete components might have to be removed
Domain analysis Aim: identify reusable components for a problem domain. identification of right kind of reusable information is a difficult problem.
Domain analysis Domain analysis identifies: objects, operations and relationship among them. Consider airline reservation: objects are seats, flights, airports, crew, meal orders Operations are scheduling a flight, reserving a seat, assigning a crew to a flight, etc.
Domain analysis Analysis of an application domain: to identify the reusable components Actual construction of reusable components for a domain is called domain engineering.
Reuse at organization level Reusability should be a standard part in: specification, design, implementation, test, etc. Ideally there is a steady flow of reusable components: in practice, things are not so simple.
Reuse at organization level Extracting reusable knowledge from past projects: presents difficulties not encountered in working with a current project typically original developers are no longer available for consultation.
Summary Basic issues in reuse: Component creation Component indexing Search Understanding Adaptation Repository maintenance
Summary Domain analysis: Creation of highly reusable components is a very difficult problem a promising approach is domain analysis Domain analysis: aims to identify reusable components for a problem domain
Summary Application generators: translate specifications into application programs. facilitate reuse not very flexible, if new concepts need to be supported.
Summary Reuse at organization level assess product’s potential for reuse refine product for greater reusability integrate product with reuse repository