Concepts

Component

Metadata describing a building block of the software system.

A component consists of:

• A name
• An optional set of tags
• Zero or more dependency selectors
• A start function
• An optional stop function

Configuration

A collection of components, describing a system.

Tag

Identifies components. Every component has a name, which is a tag, and can have additional tags. Tags can have is-a relationships, so that they form graphs.

Selector

Criteria to select components in a configuration. A selector consists of one or more tags. A components matches a selector if it provides all tags in the selector.

Dependency

A selector specifying a component or set of components that a component depends on.

Dependencies usually are unique, requiring exactly one matching component in the configuration. Optional dependencies specify a set of zero or more matching components.

Dependency Graph

A data structure derived from a configuration, by resolving component dependencies, and detecting unsatisfied and ambiguous dependencies.

Component Instance

A concrete instance of a component, a value returned from the component's start function.

System

A map of component instances, obtained from the configuration with the help of a dependency graph.