Enterprise Application Integration (EAI) - Guide to Cloud Computing for Business and Technology Managers - page 98

c. Connector—In this approach, the application provides an access
point that allows either a message or invocation on an interface to
be passed into the application; a connector is more than an interface
providing additional capabilities like error handling and validation
checking, conversion and transformation of data into appropriate
format, and managing state information enabling guaranteed deliv-
ery or graceful recovery. Many applications do not have a predefined
or prebuilt entry point into the application. In such cases, one may
need to use data files, databases, user interfaces, or memory as the
entry point for the injection of the request. It is at this point that the
correct integration model must be selected—presentation, data, or
functional—to build the right connector based on the internal struc-
tures of the application.
4.2.1.2 Modes of Communication
The flexibility of systems is critically dependent on the modes of communi-
cations 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 com-
munications are as follows:
1. Synchronous communication—This 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 communication
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 network 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. Transmit
c. Polling
2. Asynchronous communication—This 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 communica-
tions does not demand a high degree of coupling and also does not
require the sender to coordinate the communications with its inter-
nal processing. It is used when the communication of information is
required without the need to coordinate activities or responses.