Context Data Model 2.0

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Version

• This page describes version 2.0 of the Context Data Model
• See Context Data Model 1.0 for the released Higgins 1.0 version

Introduction

Although the CDM can be used for almost any kind of data, the focus of CDM is to provide a foundation for integrating, unifying, and sharing identity-related data. In particular we are focused on information about a person, a group or an entire organization. This might include contact information, authentication data, preferences, email addresses, interests, employer-related information. An object representing a single person, might have relationships to other objects and other people in the same or different data contexts.

See:

• Higgins Data Model Intro (PPT) for an overview.
• Context Data Model Background for information about motivations and design goals.

Relationship to RDF

The Context Data Model (CDM) encompasses the core semantics of the W3C's Resource Description Framework (RDF); anything expressible in RDF is expressible in the CDM although the converse isn't true.

Most of the subtle but important differences between CDM and RDF are derived from differences in the choice of identifiers used to identify objects in each model. RDF is based on pure HTTP URIs, whereas CDM is based on a more generalized URI called a UDI. Objects identified by URIs in RDF are called Resources, whereas in CDM they are identified by UDIs and are called Entities.

CDM entities, attributes and values form interconnected graphs of objects. A graph is contained in a data set called a Context. This is analogous to an RDF dataset. Within this main context graph may live zero or more sub-graphs known as sub-contexts. Each of these sub-contexts is analogous to the Named Graph extensions to RDF. Like named graphs the contexts are themselves entities that may have arbitrary attributes and values.

The CDM differs from RDF on a syntactic (semantically lossless) level. In RDF an object may have N properties of type T each of which has a single value whereas in the CDM an object may only have 0..1 property of type T, and if the property exists it has 1..N values. Further, in the CDM these properties are called Attributes.

Key Concepts

Top level concepts

1. Context - a container of objects called Entities. Contexts are a special kind of entity identified by a ContextId. Contexts may have sub-Contexts. A given EntityId may occur in multiple sub-Contexts (or Contexts).
2. Entity - an object identified within a Context by an EntityId.
3. Attribute - a property of an Entity. Attributes of an Entity are distinguished from one another by its AttributeId. Attributes have 1..N values. These values may be simple (literals) or complex (other Entities).
4. Data Range - a definition of a kind of simple, literal Attribute value. Generally a syntax restriction on one of the XML Schema datatypes.

cdm.owl

CDM uses concepts that, while they can be approximated in OWL, are unique to CDM and are not compatible with existing RDF/OWL data sources. These are described in a file called Cdm.owl 1.1. This cdm.owl file is provided only as a description using RDF/OWL of the foundational concepts of CDM (e.g. "Entity"). However the cdm.owl file should not be imported or used in creating ontologies, it was created only as a description of the CDM metamodel itself.

Misc

• Context Data Model 1.1 Open Issues
• Context Data Model Related Resources

See Also

• Higgins Data Model 1.1