Information Technology Reference
In-Depth Information
«NV_BEO»
GUI2User
«NV_BEO»
UserOps
«use»
«use»
«NV_Stub»
GUI2UserStub
«NV_Stub»
UserOpsStub
«use»
«use»
«NV_Binder»
UserOpsBinder
«NV_Binder»
GUI2UserBinder
«use»
«use»
«use»
«use»
«NV_ProtocolObject»
GUI2UserProtocol
Object
«NV_ProtocolObject»
UserOpsProtocol
Object
«NV_Interceptor»
GeneralChannel
Interceptor
FIGURE 5.3: A channel from the GUI2User BEO to the UserOps BEO.
into a neutral format that is sent along the channel and that the server
stubs understand. The received request is then translated by the server
stub to the language of the server, and passed to it. The response from
the server follows a similar route back to the client, with the stubs again
translating the messages. The result is that the client and server objects
both think that they are talking to local objects written in their own
language.
Binders provide services to establish a distributed binding between the
BEOs communicating through the channel and to provide the trans-
parency functions that coordinate replicated object instances. There
can be a number of different dialogue styles involved in this. Thus, for
instance, the client and server binders can set up the communication
channel and the server binder can wait for requests before activating the
server object. In fact, the server binder can exhibit different behaviours
depending on the activation policy required for the server object; the
binder can create one object for every request received, or instantiate
only one object to take care of all incoming requests when the channel is
started, or it can create one server object that takes care of all requests
received during a period of time, but which terminates if it receives no
requests for a while; many other instantiation policies are possible.
A protocol object is an encapsulation of the communication capabil-
ity of the protocols, which may be a full stack of layered protocols for
a specific task, such as support for the Web Services protocol SOAP.
At a lower level, protocol objects might exploit IPv6 roaming support
 
Search WWH ::




Custom Search