Overview of Directory Service Components

· The DCE Cell Directory Service (CDS)

· The DCE Global Directory Service (GDS)

· The DCE Global Directory Agent (GDA)

The X/Open Directory Service (XDS) application programming interface is used to access the Directory Service components. A brief overview of the Directory Service components and interface is given in this section; subsequent sections in this topic describe them in more detail.

DCE Cell Directory Service

The Cell Directory Service (CDS) stores names and attributes of resources located in a DCE cell. It is optimized for local access, since most directory service queries are for information about resources within the same cell as the originator of the query. CDS is replicated - this is important for a local directory service, since the directory service must be highly available. There must be at least one Cell Directory Server in each DCE cell. The following figure shows three organizations, each with its own DCE cell.

Three One-Celled Organizations

CDS can be used to connect independent cells into a hierarchical cell configuration, as shown in the figure below, entitled Connected DCE Cell Namespaces. In this configuration, one cell's CDS acts as a higher-level directory service to connect other independent cells. The cell whose CDS acts as the higher-level directory service is known as the parent cell, while the cells connected through the parent's CDS are known as child cells.

DCE Global Directory Service

The Global Directory Service is a distributed, replicated directory service based on the CCITT X.500/ISO 9594 international standard. GDS interworks with other X.500 implementations, and can therefore participate in the worldwide X.500 directory service.

The Global Directory Service can act as a higher level directory service to connect cells, as shown in the following figure. DCE supports the use of a second standard directory service, the Domain Name Service (DNS), which is widely used in the Internet community. It, too, can act as a higher level connector of DCE cells.

Connected DCE Cell Namespaces

DCE Global Directory Agent

The Global Directory Agent is the intermediary between a cell's CDS and the rest of the world. It takes a name that cannot be found in the local cell and finds the foreign cell in which the name resides, using GDS, DNS, or CDS, depending on where the foreign cell is registered. The following figure gives a functional picture, including the use of GDAs, of the configuration shown in the figure above, entitled Connected DCE Cell Namespaces.

Use of Global Directory Agents

DCE Directory Service Application Programming Interface

DCE programmers use the X/Open Directory Service (XDS) application programming interface to make all Directory Service calls. The XDS library knows, based on the format of the name to be looked up, whether to direct the calls it receives to the Global Directory Service or to the Cell Directory Service (see the following figure). XDS uses the X/Open Object Management (XOM) application programming interface to define and manage its information.

XDS: Interface to GDS and CDS