Next: Mapping Information
Up: The Extended Data
Previous: The Extended Data
The model of the database contains the following kinds of
- Domain names, indicating which column of which table
defines the possible values, together with an indication of the type
of the domain values (string or number) and whether the individuals
in that domain are animate or inanimate, for example:
ass_mark isDOMAN [ assign_mark![mark], number, inanimate ].
- Table definitions, providing the names of the tables,
and the named of the columns together with the domains of the values
of those columns, for example:
assignment isTABLE [ assno :ass_num,
weekdue :ass_weekdue ].
- key fields in the tables:
assignment hasKEY [ course ].
assignment hasKEY [ assno ].
This is used in the optimisation of the queries. In principle, if a
table has multiple keys, then the keyfields could all be provided in
a list. However, the code is not currently written to exploit this.
Chris Fox, September 1995