Production Rules of CSDGM

A production rule specifies the relationship between a compound element, and data elements and other (lower-level) compound elements. Each production rule has a left side (identifier) and a right side (expression) connected by the symbol "=", meaning that the term on the left side is replaced by or produces the term on the right side. Terms on the right side are either other compound elements or individual data elements. By making substitutions using matching terms in the production rules, one can explain higher-level concepts using data elements.

The symbols used in the production rules have the following meaning:

=	is replaced by, produces, consists of
+	and
[|]	selection - select one term from the list of enclosed terms (exclusive or).
	Terms are separated by "|".
m{}n	iteration - the term(s) enclosed is(are) repeated from "m" to "n" times
()	optional - the term(s) enclosed is(are) optional


a = b + c		"a consists of b and c"
a = [b | c]		"a consists of one of b or c"
a = 4{b}6		"a consists of four to six occurrences of b"
a = b + (c)		"a consists of b and optionally c"

Interpreting the production rules:

This page excerpted from the introductory material of the CSDGM Version 2 - FGDC-STD-001-1998

Hugh Phillips, 10/1/2000