6 Information language

The information language comprises concepts, rules and structures for the specification of an ODP system from the information viewpoint.

An information specification defines the semantics of information and the semantics of information processing in an ODP system.

In this Reference Model, prescription in the information viewpoint is restricted to a small basic set of concepts and rules addressing the scope and nature of information specifications.

The information language contains the concepts of ITU-T Rec. X.902 | ISO/IEC 10746-2 and those defined here, subject to the rules of 6.2.

6.1.1 Invariant schema: A set of predicates on one or more information objects which must always be true. The predicates constrain the possible states and state changes of the objects to which they apply.

NOTE - Thus, an invariant schema is the specification of the types of one or more information objects that will always be satisfied by whatever behaviour the objects might exhibit.

6.1.2 Static schema: A specification of the state of one or more information objects, at some point in time, subject to the constraints of any invariant schemata.

NOTE - Thus, a static schema is the specification of the types of one or more information objects at some particular point in time. These types are subtypes of the types specified in the invariant schema.

6.1.3 Dynamic schema: A specification of the allowable state changes of one or more information objects, subject to the constraints of any invariant schemata.

NOTES

1 Behaviour in an information system can be modelled as transitions from one static schema to another, i.e., reclassification of instances from one type to another.

2 In the information language, a state change involving a set of objects can be regarded as an interaction between those objects. Not all of the objects involved in the interaction need change state; some of the objects may be involved in a read-only manner.

An information specification defines the semantics of information and the semantics of information processing in an ODP system in terms of a configuration of information objects, the behaviour of those objects and environment contracts for the system.

An information object template references static, invariant and dynamic schemata. The relationships between information objects can be modelled as part of the state of those information objects. Information objects are either atomic or are represented as a composition of component information objects. The state of the composite object is represented by the combined state of its component information objects. An atomic information object template represents a concept for which there is no model at a particular level of abstraction. A composite information object represents a derived concept expressed in terms of other concepts. Since object composition includes encapsulation, an information object that is a component of one composite object cannot be a component of another. Therefore information objects resulting from the instantiation of a composite information object template only exist as part of the instantiated composite object and have no meaning outside it.

Allowable state changes specified by a dynamic schema can include the creation of new information objects and the deletion of information objects involved in the dynamic schema. Allowable state changes can be subject to ordering and temporal constraints.

NOTE - The result of accessing the state of one or more information objects can be modelled as the creation of a new information object.

In an information specification, the configuration of information objects and the behaviour of those objects need not be suitable for distribution (e.g., there need not be any concept of failure or location for information interactions).

NOTE - If an information notation uses the concept of interface, any interfaces defined cannot themselves be reference points; thus there is no commitment to the interfaces appearing in an implementation.

Conformance statements in information specifications require that the behaviour of an ODP system is conformant to a particular set of invariant, static and dynamic schemata.

An implementor claiming conformance must list the relevant engineering reference points which give access to the system and the engineering and computational specifications which apply to them. By this act the identified reference points become conformance points. The interactions at these conformance points can then be interpreted in information language terms to check that they are consistent with the invariant, static and dynamic schemata.

Information specifications can be applied to all four classes of reference point (programmatic, perceptual, interworking, and interchange reference points) identified in ITU-T Rec. X.902 | ISO/IEC 10746-2.