Identifiers

CAT identifies catalogues and components by various sorts of identifiers; INTEGER numbers, each with a unique value. In the calling arguments for the subroutines the following names are usually used for the various sorts of identifier:

GI	-	generic,
CI	-	catalogue,
PI	-	part (column or parameter),
FI	-	column (F for field),
QI	-	parameter,
EI	-	expression,
SI	-	selection

The following rules apply:

1. A generic identifier may be substituted by any type of identifier,

2. there are circumstances where it is sensible to consider columns and parameters to be a single sort of component; in these circumstances, components and parameters are referred to collectively as parts; a part identifier may be substituted by either a column or a parameter identifier.

3. an expression identifier may be substituted by a field, parameter (or hence part) identifier.