Various technologies and techniques are disclosed for providing a framework with a common set of domain-specific entity identifier types that object models representing conceptually similar entities from a domain can use to correlate to model-specific object instances. A particular model-specific object instance of a particular one of the object models can be retrieved using a common set of domain-specific entity identifier types. An instance of a particular domain-specific entity identifier type can be retrieved from a corresponding one of the model-specific object instances. One or more extensibility mechanisms allow third parties to extend the set of domain-specific entity identifier types.