odel, a structure of types and relations against which instances
&gt;    of the types and relations can be stored. Definitions of the types and
&gt;    relations are in natural language. Some constraints are defined, usually
&gt;    in terms of the cardinality of relationships.
&gt;
&gt;  - Ontology, types, relations, and possibly instances of those together
&gt;    with axioms, usually in First Order Logic, that define the rules that
&gt;    apply to members of the types and relations.
&gt;
&gt;Data Models