A telephone book is a familiar type of directory, a card catalog in a library is another, and a department store catalog still another. In a computerized environment, a directory is a specialized database that stores collections of information about objects. Although a directory is a database, it is designed very differently from a relational database. Directories are primarily read-focused . Typical use of a directory involves a relatively small number of data updates, and a potentially very large number of data retrievals.
Directories handle relatively simple transactions on relatively small units of data .
For example, an application might use a directory to store and retrieve an e-mail address, a telephone number, or a digital portrait. By contrast, a relational database is designed to handle large and diverse transactions using large data items and many operations. Directories are location-independent . Directory applications expect, at all times, to see the same information throughout the deployment environment regardless of which server they are querying. If a queried server does not have the information locally, then the server must either retrieve it or point the client application to it transparently.