Off-the-shelf components used as building blocks for larger software.

• Examples: sort verb in COBOL, library functions such as sqrt, Lisp system functions, IMSL library.

• Booch components (based on abstract data types) are used somewhat.

• Inheritance in object-oriented programming can be considered to be in this category.

• Abstraction: must provide specifications (aside from code) of what the components do.

• Selection: Manuals not so good for selection; need good indexes and automation.

• Specialization: Edit code or parameterize, e.g. by specifying a ``contents'' type. Problem: how much parameterization is possible?

• Integration: Name conflicts may be a problem. Unix pipes are another form of integration.

• Cognitive distance: small if user already understands the concept ( e.g., matrix inversion).

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