Naming and Directory Services

A Naming Service provides a mechanism for giving names to objects so that you can retrieve and use those objects without knowing the location of the object. Objects can be located on any machine accessible from your network, not necessarily the local workstation.

A real-world example is a phone directory. It stores telephone numbers against names and addresses. To find someone's phone number is simply a matter of using his or her name (and possibly address) to identify the entry in the phone book and obtain the stored phone number. There are a few complications, such as finding the right phone book to look in, but it is essentially fairly simple.

Incidentally, naming services have a similar problem to that of finding the right phone book. This is known as obtaining a context. A name can only be found if you examine the right context (phone book).

A Directory Service also associates names with objects but provides additional information by associating attributes with the objects.

The yellow pages phone directory is a simple form of a directory service. Here, businesses often include advertisements with additional information such as a list of products sold, professional qualifications, affiliated organizations, and even location maps for their premises. These attributes add value to the name entry. A directory service will normally provide the ability to find entries that have particular attributes or values for attributes. This is similar to searching the yellow pages phone book for all plumbers running a 24-hour emergency service within a certain area.

Yellow page style phone books also store names under different categories—for example, plumbers or lawyers. Categorizing entries can simplify searching for a particular type of entry. These categorized entries are a form of sub-context within the directory context of the local phone book.