Attribute Substring Index

A substring index is a type of index that is used to keep track of which entries contain specific substrings. Index keys for a substring index consist of six-character substrings taken from attribute values and the corresponding values are a list containing the entry ID of the entries containing those substrings. The attribute's substring matching rule is used to normalize the values for the index keys, and substring indexes cannot be defined for attributes that do not contain substring matching rules.