Rel version 0.3.20 released

This version of Rel makes major changes to the type system. It is now
possible to create subtypes of the built-in INTEGER, BOOLEAN,
RATIONAL, and CHARACTER types. The <, <=, >, >=, =, <>, AND, OR, XOR,
NOT, +, -, *, and / symbolic operators have been mapped to named
operators, all of which have a name prefixed with OP_. This makes it
straightforward to create appropriate operators for user-defined types
and subtypes, simply by defining new OP_ operators.

At this time, there is a slight overall performance penalty associated
with being able to subtype the built-in types, and a noticeable
performance hit associated with using subtyping-by-constraint on the
INTEGER, BOOLEAN, and CHARACTER types. For teaching purposes (Rel is
mainly used as a teaching tool) this shouldn't be a problem. If
you're using Rel to run your company payroll, however, the performance
hit may be of concern. This version of Rel makes no attempt to
optimise performance. As such, it is advisable to do appropriate
testing before using this version of Rel in production settings.
Future updates will implement appropriate optimisations.

Also, this version is the first to implement TCLOSE. However, it is
quite inefficient as it is based on the TRANCLO() example from page
175 of The Third Manifesto, 3rd Edition. However, for
teaching-oriented examples and the like, performance should be
acceptable.

For more information, or to download Rel, see
http://dbappbuilder.sourceforge.net/Rel.html