physical instance in a way that facilitates processing. Function In the real-world context of engineering online systems, identity management can involve five basic functions: The pure identity function: Creation, management and deletion of identities without regard to access or entitlements; The user access (log-on) function: For example: a smart card and its associated data used by a customer to log on to a service or services (a traditional view); The service function: A system that delivers personalized, role-based, online, on-demand, multimedia (content), presence-based services to users and their devices. Identity Federation: A system that relies on federated identity to authenticate a user without knowing their password. Audit function: Monitor bottlenecks, malfunctions and suspect behaviour. Pure identity A general model of identity can be constructed from a small set of axioms, for example that all identities in a given namespace are unique, or that such identities bear a specific relationship to corresponding entities in the real world. Such an axiomatic model expresses "pure identity" in the sense that the model is not constrained by a specific application context. In general, an entity (real or virtual) can have multiple identities and each identity can encompass multiple attributes, some of which are unique within a given name space. The diagram below illustrates the conceptual relationship between identities and entities, as well as between identities and their attributes. In most theoretical and all practical models of digital identity, a given identity object consists of a finite set of properties (attribute values). These properties record information about the object, either for purposes external to the model or to operate the model, for example in classification and retrieval. A "pure identity" model is strictly not concerned with the external semantics of these properties. The most common departure from "pure identity" in practice occurs with properties intended to assure some aspect of identity, for example a digital signature or software token which the model may use internally to verify some aspect of the identity in satisfaction of an external purpose. To the extent that the model expresses such semantics internally, it is not a pure model. Contrast this situation with properties that might be externally used for purposes of information security such as managing access or entitlement, but which are simply stored, maintained and retrieved, without special treatment by the model. The absence of external semantics within the model qualifies it as a "pure identity" model. Identity