OSF DCE Administration Guide--Core Components

Introduction to the DCE Directory Service
Figure 11-3. Sample CDS Namespace Hierarchy
/.:
hosts
subsys
dce
The complete specification of a CDS name, going left to right from the cell root to the
entry being named, is called the full name. Each element within a full name is separated
by a / (slash) and is called a simple name. For example, suppose the /.:/hosts directory
shown in Figure 11-3 contains an entry for a host whose simple name is bargle. The
CDS full name of that entry is /.:/hosts/bargle. Multiple consecutive slashes are turned
into a single slash in a full name.
Multiple directory levels enable flexibility in distributing, controlling access to, and
managing many names. A directory hierarchy also reduces the probability of duplicate
names. For example, the names /.:/subsys/Hypermax/printQ/server1 and
/.:/subsys/ABC/spell/server1 are unique.
11.5.2 GDS Names
The operation of GDS is similar to that of CDS, but some important differences exist in
the structure of names and the ways they can be looked up. Like CDS, GDS has a server
process that provides access to and management of names. This process is called a
Directory System Agent (DSA). The combined knowledge of all DSAs that participate
in the same global directory service implementation is called the Directory Information
Base (DIB). This collective knowledge is viewed as a single global directory consisting
of many entries.
Information exists in the global directory in the form of a rooted hierarchy that is called
a Directory Information Tree (DIT). The DIT is similar to a CDS namespace. However,
unlike a namespace, which has no inherent rules regarding structure and content, the
GDS hierarchy is influenced by a set of rules that is called a schema. Every X.500 DSA
must define a standard schema to which all of the entries in its portion of the DIB
conform.
Although the X.500 standard does not mandate a specific schema, it does make general
recommendations that are based largely on existing X.400 standards for electronic mail.
For example, countries and organizations should be named close to the root of the DIT;
people, applications, and devices should be named further down in the hierarchy. GDS
supplies a default schema that complies with these recommendations.
Every GDS entry has a distinguished name, which uniquely and unambiguously
identifies that entry. The distinguished name consists of a sequence of valid Relative
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