Database rules and time: some proposed extensions to the SQL standard
O'Neill, Liam (1994) Database rules and time: some proposed extensions to the SQL standard. Master of Science thesis, Dublin City University.
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The subject of this thesis is the incorporation of temporal
semantics into database rules and how the resultant syntax
might be reconciled with the evolving SQL standard. In particular, it explores time-driven rules and the time-relationship between triggering events and associated actions.
A review of the key research results in the area of
database rules and the syntax developed for the major
prototype implementations is conducted, and a working
syntax , free of any limitations within the SQL standard,
developed. Next, an operational definition is evolved
through the application of this working syntax to two
sample domains rich in 'temporal rules'. In each case a
graphical representation of the domain is presented using
an adapted object-oriented modelling technique followed by
a mapping into the working temporal syntax.
Attention is then turned to the SQL-92 standard and its
future successor SQL3. An assessment is made of their
implications for the working syntax developed in the
earlier chapters - with particular reference to the
specification of time and the use of database triggers.
When an attempt was made to re-cast the working syntax into
SQL, a satisfactory mapping, which succeeded in preserving
the semantics of the original, could not be achieved.
Support for time-based triggers; cyclic operations;
delayed actions and rule lifetimes necessitated the
development of appropriate modifications to the basic SQL3
draft syntax. The proposed extensions capture all of the
semantics required for the specification of time-based
The example applications indicated that an extended SQLcompliant
language approach allied to a sound objectoriented
modelling formalism had a broad applicability.
Furthermore, it was apparent that the addition of a
temporal dimension to rule actions was a key enabling
factor in increasing their semantic power.
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