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The PCD is the central storage mechanism of the portal. It stores data from portal content objects such as roles, pages, worksets, system landscape, and many more. The details of such data are in portal archive (PAR) files that have been deployed on the portal.
This storage mechanism enables separation of data that describes content, such as, names, fields, values, and so on, from the technical implementation of the content.
From the architectural point of view, the PCD is a logical layer of services that interfaces with portal components on one hand, and with the database shared by the portal and the SAP Web Application Server, on other.
The PCD is comprised of the following:
· Semantic Layer
The Semantic layer is comprised of services (portal services) that define metadata describing portal content objects; however, the information on the origins of the content is located in the database implemented for the PCD. Also in this layer are portal applications that interface with the portal client. The semantic layer creates data for the generic layer.
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· Generic Layer
The Generic layer (portal services) consists of services that enable the portal to implement the content. The location of various routines, other services, components and portal applications, form part of the implementation details. Origins and sources of specific data, such as code to be implemented, are located in the database.
· Persistence layer
The Persistence layer (portal services) is also a service that interfaces with the Generic layer and the database for the portal. This service obtains details of objects from the database, parses the information, and then encapsulates it for further processing in the portal at runtime.
The PCD storage mechanism enables content developers to concentrate on creating and adding business processes to the portal, without worrying about how it is implemented.
The following illustration shows the various layers in the PCD:
The PCD is Java Naming Directory Index (JNDI) compliant and features schema support for object type definition for creating object hierarchies.
As an extension to the JNDI, PCD offers a feature called delta link, enabling one object to inherit properties from another so that changes to the source object are automatically updated in the target object (the delta link object). In short, the PCD simply holds a hierarchy of objects with properties.
In addition to storage of objects and attributes, the PCD offers several features such as:
· Attributes of properties
Properties such as personalization can have extended attributes. Such a property can be modified by end users. The attributes control what the portal does with the values.
· Personalization
Personalization objects are user-based, relating to the specific instance of the object. When a user modifies the object, the changes apply only to that useru2019s instance of the object. The changes do not apply to the same object being used by others.
Personalized objects are stored in a way that enables personalization changes to be merged automatically when a specific user asks for a specific personalized object, that is, their view of an object.
· Internationalization
Objects can have u2018textu2019 properties, which may have multiple values associated with multiple languages. Thus, when an object is requested, the text in the appropriate language is automatically merged to the returned object.
The PCD interfaces with several services, such as User Management Engine, Access Control Lists (ACLs), messaging (for cache invalidation notifications), and transport mechanism.
The PCD is capable of working with several portals distributed over several physical machines, and connecting to the same database. It handles the complexity of maintaining a valid single cache for the distributed portals.
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