Portal Content Directory (PCD) Overview 
The Portal Content Directory (PCD) stores portal objects, and provides an API to enable applications to perform lookups and modify the PCD.
The following shows the major components involved when working with the PCD:
Portal Database: Stores portal objects.
Portal Content Directory (PCD): A JNDI provider that provides an API for querying portal objects.
Semantic Object Providers: Each provider defines the logic for returning Java objects when querying a specific portal semantic object. A semantic object is defined by its com.sap.portal.pcd.gl.ObjectClass property.
Portal Content Model (PCM): A set of common interfaces for all portal objects.
Administration editors, for example, request PCM interfaces when querying the PCD and other repositories for portal objects. These editors need higher level interfaces than those provided by the PCD, but do not need the specific interfaces for the different semantic objects.
More information: Portal Content Model (PCM)
An application can look up a PCD object and request that a variety of Java interfaces be returned. More information: How PCD Lookups are Performed
More Information
Information about accessing the PCD with the help of an API: Accessing the PCD
Information about creating PCD content using XML: XML Content and Actions