Production Rule
Note
Indexing Service is no longer supported as of Windows XP and is unavailable for use as of Windows 8. Instead, use Windows Search for client side search and Microsoft Search Server Express for server side search.
A production rule defines a nonterminal symbol in terms of other nonterminal symbols and terminal symbols. A production rule has this form:
left side = right side ;
The equal sign (=) separates the definition (right side) from the defined symbol (left side), and a semicolon terminates the rule. As the result of a production rule, right side replaces left side wherever left side appears in a production rule.
To produce a valid instance of a query-language construct, successively (even recursively) apply production rules until only terminal symbols remain.
The definition (right side) consists of a combined sequence of nonterminal and terminal symbols that uses several operators. The following table describes the operators.
| Operator | Name | Example | Meaning |
|---|---|---|---|
| | | Alternative | a | b | Either a or b |
| implicit | Concatenation | a b | a followed by b; ab |
| - | Except | abc - b | abc less b; ac |
| * | Occurrences | 5 * a | Five as; aaaaa |
There are four bracketing constructs to represent grouping, repetition, and optional inclusion. The following table describes these constructs.
| Construct | Name | Example | Meaning |
|---|---|---|---|
| ( … ) | Grouped | ( a | b ) c | ac or bc |
| [ … ] | Optional | [ a ] b | ab or b |
| { … } | Repeated zero or more times | a { a } | a, aa, aaa, … |
| { … }- | Repeated one or more times | a { a }- | aa, aaa, aaaa, … |
There also are two miscellaneous constructs. The following table describes these constructs.
| Construct | Name | Example | Meaning |
|---|---|---|---|
| (* … *) | Comment | (* This is a comment. *) | Not part of the syntax specification |
| ? … ? | Special | ? Not defined ? | Not defined by EBNF |