1. A computer-implemented method for efficient retrieval of a knowledge reference, comprising: receiving a query for retrieving an entry from a directory information system, wherein the entry from the directory information system is represented in a relational database; modifying the query, by using a processor, to retrieve the entry and a representation of the knowledge reference from the directory information system, wherein the representation of the knowledge reference is in the relational database, wherein modifying the query comprises: receiving a request for a first attribute value pair; generating a database query statement to search for the first attribute value pair; and inserting an OR operator and a second attribute value pair in the database query statement, wherein the second attribute value pair includes the knowledge reference attribute and attribute value; retrieving the entry and the representation of the knowledge reference in the relational database, wherein the representation of the knowledge reference comprises remote directory server information for a partition of a directory information tree, wherein the directory information system content is partitioned among multiple directory servers; responding to the query for retrieving the entry from the relational database with the entry and the knowledge reference from the relational database; locating one or more catalog tables in the relational database for one or more searchable attributes in the directory information system; inserting a place holder in the one or more catalog tables for the knowledge reference; and displaying the entry and the knowledge reference on a display device or storing the entry and the knowledge reference in a volatile or non-volatile computer-usable medium.