Database Reference
In-Depth Information
10.2.1.2 Modes of Communication
The flexibility of systems is critically dependent on the modes of communications that are utilized
by the systems. Assuming that a
request
refers to a communication from a sender to a receiver, the
two basic options for communications are as follows:
1.
Synchronous communication
: Requires the sender of a request to wait until a reply—which is
the result of the request—is received before continuing the processing. Synchronous com-
munication between systems implies a high degree of coupling and requires the sender and
the receiver to coordinate the communications with their internal processing. A reliable net-
work infrastructure is essential for this kind of communication. It is used when the sender
requires a notification of the receipt or needs the result of the processing from the receiver.
For instance, interactive systems need a synchronous type of communication.
There are three popular types of synchronous communications:
a. Request/response
b. Tra nsm it
c. Polling
2.
Asynchronous communication
: Allows the sender to continue processing after sending the
request, without waiting for a reply to this request. The sender does not concern itself with
whether or when the request has been received, how it is processed, or the results returned
from the receiver. Asynchronous communications does not demand a high degree of cou-
pling and also does not require the sender to coordinate the communications with their
internal processing. It is used when the communication of information is required without
the need to coordinate activities or responses.
There are three popular types of asynchronous communications:
a.
Message passing
: This is used in situations where information needs to be transmitted but
a reply is not required. This needs a reliable network for guaranteed delivery.
b.
Publish/subscribe
: This is used in situations where a reply is not required, but unlike all other
cases, the recipient is determined based on the content of the request and the predeclared
interest of the receiver application. This type of communication is useful for STP type of
functional integration (see Section 10.2.2.2.3 “Straight-Through Processing (STP)”).
c.
Broadcast
: This is used in situations where again a reply is not needed, but the request
is sent to all of the applications and each of the receiver decides if it is interested in the
request/message and accordingly processes that request/message in accordance with the
business and functional logic programmed into each of the receiver system.
10.2.1.3 Middleware Options
Middleware is a software that enables disparate applications to interact with each other: it facili-
tates the communication of requests between software components through the use of predefined
interfaces or messages. The five basic types of middleware are as follows:
◾
Remote Procedure Calls (RPCs)
: Is based on the notion of developing distributed applications
that integrate at the procedure level but across a network.
◾
Database Access Middleware
: Is based on the notion of developing distributed applications
that integrate at the distributed data level whether in files or databases but across the network.
