A fundamental facility
in any computing system is the naming service - the means by
which names are associated with objects, and by which objects
are found given their names. In traditional systems, the naming
service is seldom a separate service. It is usually integrated
with another service, such as a file system, directory service,
database, desktop, mail system, spreadsheet, or calendar. For
example, a file system includes a naming service for files and
directories; a spreadsheet has a naming service for cells and
macros.
The computing environment
of an enterprise typically consists of several naming services.
There are naming services that provide contexts for naming common
entities in an enterprise such as organizations, physical sites,
human users and computers. Naming services are also incorporated
in applications offering services such as file service, mail
service, printer service, and so on. From a user's perspective,
there exist several natural and logical relationships between
these naming services. For example, it is natural to think of
naming a variety of services such as files, mail, appointment
calendar, and so on, in the context of a user. It is also natural
to think of a user in the context of a department, within a division
of an enterprise. Meaningful names can be composed using useful
arrangements of naming services reflecting these relationships.
Every name is generated
by a set of syntactic rules called a naming convention. An atomic
name is an indivisible component of a name, as defined by the
naming convention.
A compound name represents
a sequence of zero or more atomic names composed according to
the naming convention.
For example, in UNIX
pathnames, atomic names are ordered from left to right, and are
delimited by slash (`/') characters. The UNIX pathname usr/local/bin
is a compound name representing the sequence of atomic names,
usr , local , and bin
. In names from the Internet Domain Name System (DNS), atomic
names are ordered from right to left, and are delimited by dot
(`.') characters. Thus, the DNS name sales.Wiz.COM is a compound
name representing the sequence of atomic names, COM
, Wiz , sales .
The association of
an atomic name with an object is called a binding.
A context is an object
whose state is a set of bindings with distinct atomic names.
Every context has an associated naming convention. A context
provides a lookup (resolution) operation that returns an object,
and may provide operations such as for binding names, unbinding
names, listing bound names. An atomic name in one context object
can be bound to another context object of the same type, called
a subcontext, giving rise to compound names.
Resolution of compound
names proceeds by looking up each successive atomic component
in each successive context. The reader will find a familiar model
in UNIX file naming, where directories serve as contexts, and
pathnames may be compound names.
A naming system is
a connected set of contexts of the same type (having the same
naming convention) and providing the same set of operations with
identical semantics.
A namespace is the
set of all names in a naming system.
A composite name is
a name that spans multiple naming systems. It consists of an
ordered list of zero or more components. Each component is a
name from the namespace of a single naming system.
For example, the name
jurassic.eng:/export/home/jdoe/.signature is a composite
name representation made up of a host name jurassic.eng from
a host namespace, and the file name /export/home/jdoe/.signature
from a UNIX file namespace. Another example is the Internet URL
http://www.moon.org/public/index.html , which is
a composite name representation made up of the scheme-id http
from the "URL scheme-id" namespace, www.moon.org
which is the DNS name of the machine on which the web server
is running, and public/index.html which is a file
name from a file namespace.
Every name is interpreted
relative to some context, and every naming operation is performed
on a context object. A client can obtain an initial context object
that provides a starting point for resolution of names.
