The matching rule description format is described in RFC 4512, section 4.1.3, in Augmented Backus-Naur Form (ABNF). For more information about ABNF, see RFC 4234 and RFC 5234. This is the format that is used to display matching rules in the matchingRules attribute of the schema subentry, and it shows the properties that can be associated with a matching rule. The following example shows the definition of the matching rule description format:
MatchingRuleDescription = LPAREN WSP numericoid ; object identifier [ SP "NAME" SP qdescrs ] ; short names (descriptors) [ SP "DESC" SP qdstring ] ; description [ SP "OBSOLETE" ] ; not active SP "SYNTAX" SP numericoid ; assertion syntax extensions WSP RPAREN ; extensions
The matching rule description includes these elements:
The numeric OID is used to uniquely identify the matching rule in the directory server. Every matching rule must have a unique OID.
The name elements are human-readable names assigned to the matching rule that can be used to refer to it in place of the OID. A matching rule is not required to have any human-readable names. If it has only a single name, then it is enclosed in single quotes. If there are multiple names for a matching rule, each is enclosed in single quotes with spaces between the names, and parentheses around the entire set of names.
The description element is a human-readable description for the matching rule. There can be at most one description, and if it is present, it should be enclosed in single quotation marks.
The OBSOLETE flag indicates whether this matching rule should be considered available for use. If a matching rule is marked OBSOLETE, then it should not be possible to create any new attribute types or matching rule uses that reference this matching rule.
The syntax element identifies the attribute syntax with which the matching rule is associated. This is used to indicate the acceptable format for values on which the matching rule operates. More information about attribute syntaxes can be found in Understanding Attribute Syntaxes. The syntax OID must be included in all matching rule descriptions.
The extensions for a matching rule can be used to identify other properties for that matching rule that might not be included in the standard definition. The directory server does not currently support any extensions for use in matching rules.
For example, the following is the matching rule description for the standard caseIgnoreMatch matching rule:
( 126.96.36.199 NAME 'caseIgnoreMatch' SYNTAX 188.8.131.52.4.1.14184.108.40.206.15 )
In this case, the OID is 220.127.116.11. There is one name, which is caseIgnoreMatch. There is no description. The OID of the associated syntax is 18.104.22.168.4.1.1422.214.171.124.15 (which is the Directory String syntax). There are no extensions.