Schema Dynamic Maintenance In Directory Service System

With the development of Computer network and Internet applications, people can share the information and resource in world wide. For the convenience of sharing and managing the various resource and information in the network, the directory service technology came into being. Lightweight Directory Access Protocol (LDAP), as the standard protocol of directory service, becomes more and more popular. The volatility of application requires the directory service system to provide the ability of dynamic schema maintenance.Directory service system HUST-DSS supports LDAP, choosing the directory service sever of free software OpenLDAP to provide ordinary directory service, and integrating the LDAP schema management system which designed and coded by ourselves to provide schema dynamic maintenance service. In order to provide user's transplant access, HUST-DSS chooses the agent technology based on the Common Object Request Broker Architecture (CORBA), and uses the mixed-server strategy for replication management to enhance the system's availability.During the process of dynamic schema maintenance, the system should keep the consistency of LDAP schema firstly. In order to check schema consistency conveniently, the equivalent conditions of LDAP schema consistency, called Schema Invariant, are be introduced. For keeping these Schema Invariants before and after the schema maintenance, some rules for consistency maintenance are designed to control schema maintenance operations. To simplify the analysis, all schema operations are divided into two categories and the collection of basic schema operations are constructed. For every basic schema operation, schema maintenance algorithm related is provided.Besides, the system needs to keep the consistency between directory data and the schema during the process of schema dynamic maintenance. In order to reduce the delay mainly produced during data reorganization in disk, the entry popularity conception is introduced. For judging the entries'type, an entry popularity judgment strategy is proposed. The most popular entries are stored in cache, and a special cache management model is used to manage the data and the popularity information of popular entries. Based on entries'type, a strategy to maintain the consistency between directory data and the schema driven by system and user's search is used. The experiments show that this strategy can reduce the delay time to some extent in the comparison with traditional strategies.