Terms

Entities

• Component -- A computational entity: An object, module, or encapsulated collection of services.
• Host -- the main component of interest in a design task.
• Client -- A component that uses the host.
• Helper -- a component that host component relies on.
• (Sub)System -- a collection of components serving a common aggregate purpose.
• Class -- description of the common features of a family of components. Encompasses module declarations (of only one entity) and packages describing parameterized families thereof.
• Namespace -- a scoping construct to subdivide the set of names and their visibility within a system. In many languages, this is tied to other computational constructs, e.g., classes, procedures, modules, packages.
• Service -- a function, procedure, or process that performs an action requested by a client. A service is stateless if its availability and effects do no depend on internal preconditions, otherwise it is stateful.

Specifications

• Specification -- description at some level of precision for some level of abstraction of a component. Interfaces are descriptions, not code. (Beware that alternative accounts (e.g., CORBA) do treat interfaces as components.)
• Export interface -- what services/types client can use. e.g., list of methods, signatures, pre-post conditions, list of responsibilities, axiomatic constraints,
• Import specification -- what services the client needs to supply to compose/reuse the component. A description of how this component relies on connections with other components (helpers). This compositional specification of a component needs to be separated from client visible interface to support architectural reuse. Common connection rules and constraints may be abstracted as design patterns.
• Configuration specification -- description and facilities for arranging that specific context parameters be supplied to instantiate the component

Development Roles

• Producer -- component author
• Consumer -- client author
• Implementor -- author of code to coordinate helpers to obtain desired functionality.
• Architect -- (sub)system author.
• Specifier -- specification author.