2.4.1 Introduction to directories

Directory services emerged from pioneering work done in the early 1980s at the Xerox Palo Alto Research Center (PARC). The first real implementation was called Clearinghouse and was developed as part of a system architecture called Grapevine. Clearinghouse was used initially to enable users to roam around the network using a personalized desktop profile. As with many PARC inventions, this was a product ahead of its time. In essence, directories are specialized databases containing abstract content (i.e., a collection of objects). Directory services enable networked users or applications to locate resources or retrieve data using one or more attributes. The terms white pages and yellow pages are often used to describe how a directory is accessed (i.e., by name or by subject). For example, a directory of user information (e.g., a company's telephone directory) could be queried to find a person's job title, telephone number, and e-mail address by using his or her name and location as search attributes. A directory of network resources could be searched to find the location of the closest PostScript printer on the network, an ActiveX/CORBA/Java object, X.509 Certificate, or biometric data (for an authentication query).

Directories are increasingly being used to coordinate large-scale network activities, such as security policy management and configuration management data. For example, directories enable single sign-on services as part of an enterprisewide security infrastructure. The key aim of directory services is to provide fast access to a single repository of network data in...