Context Data Model 2.0

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Version 1.1

• This page describes version 1.1 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.

CDM Core Semantics

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.

The CDM includes a kind of object called a Context that has no analog in RDF. Individual Contexts can be thought of as containers of portions of the overall graph of objects. Contexts partition the data space into disjoint sets of objects. Context Provider plug-in implementations map data stored in a various kinds of data stores into objects within Context boundaries in CDM.

The CDM also 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 identified by a ContextId
2. Entity - instances of objects (as well as the Entity Classes and Attribute Classes that define them) within a Context. All are 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). Complex-valued Attributes are called Entity Relations (think "links")
4. Data Range - a definition of a kind of simple, literal Attribute value. Generally a syntax restriction on one of the XML Schema datatypes.
5. Statement - a class that allows attributes to be added to a (single) value of an Attribute of an Entity.

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