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Wherever possible, we have used existing components from the rest of the Java development environment. Adhering to this principle not only makes JNDI consistent with existing core classes in the Java platform but also reduces needless proliferation of classes.
The object-oriented nature of the Java programming language allows for an intuitive and simple API design, in which the directory service functionality is expressed as a natural extension to the more fundamental naming service functionality.
The API is structured in a tiered manner so that the application programmer interested in a certain directory service capability need not necessarily know about a more advanced capability. We have strived to keep the lower tiers simple and also make them represent the common case capability, relegating the more complex ones to the upper tiers.
This goal is important for two reasons. First, it enables Java applications to take advantage of information in a variety of existing naming and directory services such as DNS, NDS, NIS (YP), X.500, and LDAP. Second, it helps limit the appearance of any implementation specific artifacts in the API.
Providing a unified interface to multiple naming and directory services does not imply that access of unique features of a particular service is precluded. The unified API which is designed to cover the common case is still beneficial to applications that have explicit knowledge of the underlying naming or directory service. Such applications still benefit from sharing the common portions that use the API. This is analogous to applications sharing commonly used classes and yet adding needed specificity via subclassing.
This is important not only because of the diversity of directory service and naming services in the installed base that need to be supported, but also because new Java application and service programmers can export their own namespaces and directory objects in a uniform way.
We also wanted to make a variety of implementation choices possible without having the application pay for this freedom. For example, a "thin-client" might be better served by a proxy-style protocol in which the access to specific naming and directory services is relegated to a server. Whereas, a performance sensitive, resource rich client, might choose to use an implementation which directly allows it to access the various servers. However, the application should be insulated from these implementation choices. It should be possible to defer such choices even until runtime.
The Lightweight Directory Access Protocol (Internet RFC 2251) has emerged as the standard for directory access at the protocol level. All major directory vendors have products that support this protocol. An application that uses JNDI should be able to access all of the features offered by this standard. Where possible, JNDI should support conventions (such as those for specifying search queries/filters) already defined by the standard.