| class  | Association | This class allows one to relate a source and target registry object along a
 named relationship. | 
| class  | AuditableEvent | AuditableEvent instances provide a long-term record of events that effected a
 change in a RegistryObject. | 
| class  | Classification | A Classification instance classifies a RegistryObject instance by referencing
 a node defined within a particular ClassificationScheme. | 
| class  | ClassificationNode | ClassificationNode instances are used to define tree structures where each
 node in the tree is a ClassificationNode. | 
| class  | ClassificationScheme | A ClassificationScheme instance describes a taxonomy. | 
| class  | ExternalIdentifier | ExternalIdentifier instances provide the additional identifier information to
 RegistryObject such as DUNS number, Social Security Number, or an alias name
 of the organization. | 
| class  | ExternalLink | ExternalLinks use URIs to associate content in the registry with content that
 MAY reside outside the registry. | 
| class  | ExtrinsicObject |  | 
| class  | RegistryPackage | RegistryPackage instances allow for grouping of logically related
 RegistryObject instances even if individual member objects belong to
 different Submitting Organizations. | 
| class  | Service | Service instances describe services, such as web services, web sites, FTP
 servers, etc. | 
| class  | ServiceBinding | ServiceBinding instances are RegistryObjects that represent technical
 information on a specific way to access a Service instance. | 
| class  | SpecificationLink | A SpecificationLink provides the linkage between a ServiceBinding and one of
 its technical specifications that describes how to use the service using the
 ServiceBinding. |