Reuse is not a new concept. Many industries have been using reuse to improve quality and consistency and realize reduced development time and maintenance costs.
Most organizations use multiple types of reuse. Each of the types of reuse may be appropriate in different instances and with different types of content. Your models identify what type of reuse is appropriate (see Chapter 8).
Opportunistic reuse is when the author makes a conscious decision to find an element, retrieve it, and reuse it. Use opportunistic reuse when you do not have the technology to support systematic reuse, or when your content or corporate culture warrants the use of flexible reuse and choice.
Systematic reuse is planned reuse. Use systematic reuse when your content is very structured and you can explicitly identify where content is to be reused, and where you want to ensure that certain content is reused.
Locked reuse is reusable content that cannot be changed except by the original author. Use locked reuse when you want to ensure content is not changed.
Derivative reuse is content that is not reused identically; the content is changed. Use derivative reuse when you want to retain the relationships between pieces of information, but some of the content can be changed.
Nested reuse involves content that has a number of reusable elements contained within a single element. The sum of all the elements creates one element, and subsets of the element can be used to create alternate information products. Use nested reuse when you want to retain the context for alternate content or when content is a subset of other content.