Why Ontologies?

An Ontology model provides much the same information, except a data model is specifically related to data only. The data model provides entities that will become tables in a Relational Database Management System (RDBMS), and the attributes will become columns with specific data types and constraints, and the relationships will be identifying and nonidentifying foreign key constraints. What a data model does not provide is a machine-interpretable definition of the vocabulary in a specific domain. Data Models will not contain vocabulary that defines the entire domain, but rather the data dictionary will contain information on the entities and attributes associated with a specific data element. This is where ontologies come in.