Snapshot, Valid- and Transaction-Time, and Bitemporal as
Modifiers
The definitions of how ``snapshot,'' ``valid-time,''
``transaction-time,'' and ``bitemporal'' apply to relations provide
the basis for applying these modifiers to a range of other concepts.
Let x be one of snapshot, valid-time, transaction-time, and
bitemporal. Twenty derived concepts are defined as follows (+E1).
- relational database
- An x relational database contains
one or more x relations.
- relational algebra
- An x relational algebra has relations
of type x as basic objects.
- relational query language
- An x relational query language
manipulates any possible x relation. Had we used
``some'' instead of ``any'' in this definition, the
defined concept would be very imprecise (-E9).
- data model
- An x data model has an x query language and
supports the specification of constraints on any x
relation.
- DBMS
- An x DBMS supports an x data model.
The two model-independent terms, data model and DBMS, may be
replaced by more specific terms. For example, ``data model'' may be
replaced by ``relational data model'' in ``bitemporal data model.''