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2.7.1.2 "OS/2 WARP and OpenDoc"
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<a name="HDR4610DCS"><H4> 2.7.1.2 COSS Services</H4></a>
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<pre width="80">
<p>
The second piece of the OMA that was standardized in the last two years
was a group of services necessary to build distributed systems, COSS,
Common Object Service Specification. These are infrastructure services
needed to build applications with distributed objects, for example,
security. It is quite similar to a telephone infrastructure. CORBA
provides the line to communicate. But there is much more infrastructure
needed for the effective use of a thereon. There must be some accounting
for example, or telephone books with yellow and white pages and much more.
These services are more or less on a operating system level and must be
implemented by vendors who want to be CORBA-compliant. The services are
all defined as IDL-based frameworks (for an explanation of frameworks, see
<a href="2.9.2#HDR4610DCD">"Compound Document Framework" in topic 2.9.2</a>) from OMG.
<p>
<p>
<B>Naming</B> <B>Services</B> Naming is a basic mechanism to locate other objects on an
ORB using humanly recognizable names. It is a binding mechanism
to bind names to object references and to resolve them. It is
an iterative process of binding naming contexts that are unique
within a namespace to an object until there is a unique name.
There are some naming mechanisms already standardized outside
OMG, for example from the OSF (Open Software Foundation)
standardization group, which has defined DCE, the Distributed
Computing Environment, an infrastructure for client/server
applications. The OMG has standardized the naming interface in
a way that existing directory services such as DCE CDS, ISO
X.500, and NIS+ could be used as an implementation. So the OMG
carefully looked at not reinventing the wheel with the
definition of these COSS services such as, DCE CDS, ISO X.500,
and NIS + being used as an implementation.
<p>
<p>
<B>Lifecycle</B> <B>Services</B> This service provides a standardized way to create,
delete, copy and mo ve objects on remote machines. This remote
creation is done by finding an appropriate factory which is able
to produce an instance of the object wanted. To copy or move an
object within a networking environment may become quite a
complex thing if all references to this object and from this
object to other objects must be maintained through the move or
copy.
<p>
<p>
<B>Persistence</B> <B>Services</B> The Persistence Service describes a standardized way
to store the data of objects independently from the underlying
datastore. Different datastores such as DB/2, Objectstore or
Bento can be plugged into this service with different adapters.
Persistence Service provides a single interface to store the
objects in all these different datastores.
<p>
<p>
<B>Transaction</B> <B>Services</B> Transaction Services provides components with
transactional control facilities to protect their resources. It
is the all or nothing philosophy allows a component to make
changes permanent after a series of succes sful activities or
to abort and to return to the original state. This is, of
course, a vital functionality necessary for business critical
parts.
<p>
<p>
<B>Concurrency</B> <B>Services</B> Concurrency Services regulates the concurrent access
to resources. It ensures that only one user at a time has the
access right to update a resources. Each resources owns a set of
locks with different access rights. This service is tightly
coupled with the Transaction Service.
<p>
<p>
<B>Event</B> <B>Services</B> Event Services enable objects to send messages to each
other, filter them, let them register interest to become
notified for specific kinds of messages. It enables objects to
interact to each other in an asynchronous way. Two roles are
defined for messaging. One is the supplier of events and the
other is a consumer of events. The message exchange is done via
an event channel. Two different models therefore are supported.
One is the push model, where the event channel is pushing the
events to all interested parties, the other one in the pull
model, where the interested parties are asking for messages on
need.
<p>
<p>
<B>Externalization</B> <B>Services</B> Externalization Service is a standardized stream
interface for objects. If objects are moving across the network
or saved, their state must be externalized in standardized way.
This enables the target to internalize and resurrect an object
in a proper way again.
<p>
<p>
<B>Property</B> <B>Services</B> Property Services enables an application and parts to
add named properties to objects at run time dynamically. These
added attributes can be used to search for objects.
<p>
<p>
<B>Query</B> <B>Services</B> Query Services are describing a standardized way to search
for objects without violating the encapsulation of the objects
internal state. To define query standardized languages, as the
ODMG-93 or SQL (with object extensions) can be used. The query
returns a collection of objects that can be traversed through.
<p>
<p>
<B>Relationship</B> <B>Services</B> Relationship Services let you associate roles and
relationship to objects also dynamically at run time. A graph
with edges and nodes can be defined to describe the relationship
between objects. Two of the relationships explicitly defined
are containment and references. These relations are very
important if objects are moved or copied. To use objects in
very different environments, it is important that relations to
other objects are not part of the code, but can be added from
outside during the run time.
<p>
<p>
<B>Security</B> <B>Services</B> Security becomes an increasing matter of complexity
together with distributed objects. Security Services defines a
C2 level of security directly built into the ORB using a third
party thrusted way of authentication and authorization, as it is
provided by Kerberos for example (DCE Security). It is expected
to become standardized early in 1996. As with the transaction
service, the security service will be built directly into the
Object Request Broker.
<p>
<p>
<B>Time</B> <B>Services</B> It is a service to synchronize time across different
machines using very similar techniques, such as the DCE Time
Service, using time servers, time clerks and more.
<p>
<p>
<B>Change</B> <B>Management</B> <B>Services</B> Change Management Services is good for tracking
and upgrading different versions of components.
<p>
<p>
<B>Trading</B> <B>Services</B> While Naming Services are the white pages of a telephone
book, Trading Services are the yellow pages. They are able to
search for objects related to their offered service.
<p>
<p>
<B>Licensing</B> <B>Services</B> Components used in a networked environment must have a
very flexible licensing mechanism that goes far beyond the tools
used today.
<p>
The COSS Services provide a stable and complete definition of an
infrastructure for distributed objects needed by mission-critical
applications. IBM will merge many of its leading edge client/server
middleware into the CORBA architecture. Products such as MQSeries, CICS
and many DCE components such as security and naming technologies from IBM,
will be used for the implementation of the COSS services.
</pre>
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