Java Reference
In-Depth Information
Key to directory services is the concept of a
context
. A context is a set of
bindings with a common name, expressed in a common way. In our filesystem
example,
/etc
is a context. A context may contain other contexts that follow
the same naming convention. For example,
/etc/sysconfig
is a context that
is a
subcontext
of
/etc
. Likewise,
multitool.net
is a subcontext of the
net
context.
A context is distinguished by having a naming convention for itself and
its subcontexts, and it must have means of creating bindings, removing
bindings, and querying or listing bindings.
Since JNDI is designed to operate across multiple naming and directory
systems, it is necessary to talk about
naming systems
and
namespaces
. A naming
system is a connected set of contexts that use the same naming convention.
Thus, Internet domain names are a naming system, UNIX filenames are a
naming system, and so on. A namespace is a set of names in a naming system.
These terms will have significance later when we'll talk about JNDI.
A naming system binds a name to a value. Directory services bind a direc-
tory object to one or more
attributes
. A naming service could be thought of as
a simple case of a directory where “name” and “value” are the attributes of the
directory object. A directory can store many more attributes (bindings) for a
given name than can a naming service. Directory services also (in general)
support the notion of searches and queries.
A
directory object
represents an object in the computing environment. This
might be a server, a printer, a user, a router, whatever. Each object would have
a set of attributes that describe the object. A
directory
is a connected set of
directory objects.
In the directories we know about (see Sections 21.3.2.4 and 21.3.2.5 for
the limits of our knowledge), directory objects are arranged in a hierarchy, so
that they serve as naming contexts as well as directory objects.
21.3.2
Now that you have seen the concepts, we can cover a few common implemen-
tations of naming and directory services.
Common Directory Services
21.3.2.1
This is probably the most familiar naming and directory system. It is used all
the time to resolve Internet host names to IP addresses, and it is commonly
used to obtain the names of mail servers for domains. It also has less often used
Domain Name Service (DNS)
