|
Overview
of CORBA Services
Relationship
Service
• The
Relationship Service allows entities and relationships to be explicitly
represented. Entities are represented as CORBA objects. The service defines two
new kinds of objects: relationships and roles. A role represents a CORBA object
in a relationship. The Relationship interface can be extended to add
relationship-specific
attributes and operations.
In addition, relationships of arbitrary degree can be defined. Similarly, the
Role interface can be extended to add role-specific attributes and operations.
• Type
and cardinality constraints can be expressed and checked: exceptions are raised
when the constraints are violated.
• The
Life Cycle Service defines operations to copy, move, and remove graphs of
related objects, while the Relationship Service allows graphs of related objects
to be traversed without activating the related objects.
• Distributed
implementations of the Relationship Service can have navigation performance and
availability similar to CORBA object references: role objects can be located
with their objects and need not depend on a centralized repository of
relationship information. As such, navigating a relationship can be a local
operation.
• The
Relationship Service supports the compound life cycle component of the Life
Cycle Service by defining object graphs.
Externalization
Service
• The
Externalization Service defines protocols and conventions for externalizing and
internalizing objects. Externalizing an object is to record the object state in
a stream of data (in memory, on a disk file, across the network, and so forth)
and then be internalized into a new object in the same or a different process.
The externalized object can exist for arbitrary amounts of time, be transported
by means outside of
the ORB, and be internalized
in a different, disconnected ORB. For portability, clients can request that
externalized data be stored in a file whose format is defined with the
Externalization Service Specification.
• The
Externalization Service is related to the Relationship Service and parallels the
Life Cycle Service in defining externalization protocols for simple objects, for
arbitrarily related objects, and for facilities, directory services, and file
services.
<<BACK
NEXT>>
|
