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Revision as of 14:25, 1 September 2008
{{#eclipseproject:technology.higgins}}
Contents
Version 1.1
- This page describes the Higgins 1.1 Context Data Model
- See Context Data Model 1.0 for the released Higgins 1.0 version
Introduction
The Context Data Model (CDM) is a portion of the Higgins Data Model.
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
The Context Data Model defines these concepts:
- Attribute
- Attribute Definition
- Context
- ContextId
- Context Relation
- Context Correlation
- Data Range
- Entity
- EntityId
- Entity Relation
- Entity Correlation
higgins.owl and cdm.owl
The CDM model is a set of concepts. From 1.1M4 forward, we divide this set of concepts into two subsets. The first subset contains concepts that can are expressed in OWL1.1 and can be directly imported and used as a base ontology by RDF/OWL data sources and systems. These are contained in the file higgins.owl, a file that has been nicknamed HOWL (see HOWL 1.1). HOWL describes the semantic concepts used in the CDM.
The second subset contains concepts that, while they can be described 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
HOWL 1.1 is an abstract (sometimes called an "upper") ontology for identity information. It is abstract in that it doesn't describe any concrete attributes such as "email address" or "first name". It also doesn't define very specialized classes of objects such as "calendar event" or "student", "movie", "book", etc. These are left to Context Providers to define for themselves.
Building on HOWL 1.1
Developers must create specialized ontologies based on HOWL that describe specific concrete domains.
For example, if a developer wanted to describe a CRM database, she would create an OWL ontology that would describe the data objects in the CRM database. This CRM database is called a Context in Higgins. If, for example, the database contained records about customers and those customers had full-names and email addresses, then the developer would define "Customer" as a sub-class of Entity and "full-name" and "email" as kinds of Attributes.