8. Computer apparatus for specifying patterns in a target domain, comprising: a processor providing a meta-class defined for patterns, the meta-class being a class in a meta model of a target domain, each pattern having one or more pattern roles representing instances of respective interfaces, the pattern roles including any of: a component role representing an instance of an interface in the target domain, a composite role representing an instance of a class in the target domain that implements the component interface and composes instances of that interface, a leaf role representing an instance of the target domain class that implements the component interface, and a compose role representing an instance of the target domain operation defined by the class represented by the composite role; the processor providing a property of the meta-class as a respective meta-property for each pattern role; in computer memory: one or more connectors between meta-properties to represent relationships between pattern roles; and one or more associations for representing high level relationships between pattern roles in a manner simplifying pattern specification.
8. Computer apparatus for specifying patterns in a target domain, comprising: a processor providing a meta-class defined for patterns, the meta-class being a class in a meta model of a target domain, each pattern having one or more pattern roles representing instances of respective interfaces, the pattern roles including any of: a component role representing an instance of an interface in the target domain, a composite role representing an instance of a class in the target domain that implements the component interface and composes instances of that interface, a leaf role representing an instance of the target domain class that implements the component interface, and a compose role representing an instance of the target domain operation defined by the class represented by the composite role; the processor providing a property of the meta-class as a respective meta-property for each pattern role; in computer memory: one or more connectors between meta-properties to represent relationships between pattern roles; and one or more associations for representing high level relationships between pattern roles in a manner simplifying pattern specification. 9. Computer apparatus as claimed in claim 8 further comprising constraints specified between pattern roles in the context of the pattern meta-class.