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_. Any 'a + b' is translated to 'OP_PLUS(a, b)', 'a - b' becomes 'OP_MINUS(a, b)', 'a >= b' turns into 'OP_GREATERTHANOREQUALS(a, b)' and so on. 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
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