Matching rules are used by the directory server to compare two values for the same attribute, that is, to perform matching operations on them. There are several different types of matching rules, including:
These matching rules are used to determine whether two values are logically equal to each other. Different implementations of equality matching rules can use different criteria for making this determination (for example, whether to ignore differences in capitalization or deciding which spaces are significant).
These matching rules are used to determine the relative order for two values, for example, when evaluating greater-or-equal or less-or-equal searches, or when the results need to be sorted.
These matching rules are used to determine whether a given substring assertion should match a particular value. A substring assertion is composed of at least one element from the following sets: at most one subInitial element, zero or more subAny elements, and at most one subFinal element.
These matching rules are used to determine whether two values are approximately equal to each other. This is frequently based on “sounds like” or some other kind of fuzzy algorithm. Approximate matching rules are not part of the official LDAP specification, but they are included in the directory server for added flexibility.