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Data Model |
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A data model formally defines the data elements and the relationships between them for a domain of interest A data model describes how data is represented and accessed. Usually data models are specified in a data modeling language.
In the ANSI Four Schema Model there are four types of data model:
- External Schemas: A collection of inconsistent requirements from individual stakeholders
- Conceptual Schema: A consistent, but usually incomplete, consolidation of requirements
- Logical Data Model: A consistent and complete description of a data model independent of any particular implementation
- Physical Data Model: An implementation targeted at a particular technology (such as Oracle or an OODB)
The activity of Data Modelling is usually concerned with realising an implementation of a working model. As such it is important to Information Architecture but not essential. In many ways the work of the Information Architect can be thought of as defining the constraints of the Conceptual Schema, discovering who can contribute External Schemas and drawing out from them a description of what they feel is important. The Data Modeller then takes this set of requirements and creates a Logical Data Model that fulfils them.
Relation to data form
When defining a data form it is important to define the physical media, encoding, entity definitions, structure, reference integrity and conventions. The data model covers an important part of this picture, however most definitions of format do not explicitly define which elements are to be included.
The most flexible approach is to define the structure in the same way that the data model is described. This allows this part of the format to be clearly defined without restricting the structure described. In addition it lets future applications select an alternate form of the data, for example one that works better for remote operations.
Links to this page
The following pages link to here: ANSI Four Schema Model, Cardinality, Complexity, Computer Science, Conceptual Schema, Data Convention, Data Footprint, Data Form, Data Migration, Data Model, Data Modeling Language, Data Repository, Data Type, Database, External Schemas, Format, Implementing IA, Information Architect, Information Architecture, Information technology, Logical Data Model, Mandatory Attribute, Model, Online analytical processing, Optional Attribute, Physical Data Model, Relationship, Theory, Uses for IA, XML