Enterprise Service Bus (ESB) - Guide to Cloud Computing for Business and Technology Managers - page 199

ESB can provide asynchronous and reliable messaging to a Web Service
invocation. This means that the requestor can receive acknowledgment of
assured delivery and communicate with enterprises that may not be avail-
able. A SOAP/JMS Web Service is a Web Service that implements a JMS
queue-based transport. As in the case of the SOAP/HTTP, the SOA/JMS
service bus enables service requestors and providers to communicate using
different protocols.
9.2.5 Connectivity and Translation Infrastructure
For the most part, business applications in an enterprise are not designed
to communicate with other applications. There is often an impedance mis-
match between the technologies used within internal systems and with
external trading partner systems. In order to seamlessly integrate these
disparate applications, there must be a way in which a request for infor-
mation in one format can easily be transformed into a format expected by
the called service. For instance, in Figure 9.1, the functionality of a J2EE
application needs to be exposed to non-J2EE clients such as .NET applica-
tions and other clients. In doing so, a Web Service may have to integrate
with other instances of ESs in an organization, or the J2EE application itself
may have to integrate with other ESs. In such scenarios, how the application
exchanges information with the ESB depends on the application accessibil-
ity options. There are three alternative ways an application can exchange
information with the ESB:
1. Application-provided Web Service interface : Some applications and leg-
acy application servers have adopted the open standard philosophy
and have included a Web Service interface. WSDL defines the inter-
face to communicate directly with the application business logic.
Where possible, taking a direct approach is always preferred.
2. Non-Web Service interface : The application does not expose business
logic via Web Services. An application-specific adapter can be sup-
plied to provide a basic intermediary between the application API
and the ESB.
3. Service wrapper as interface to adapter : In some cases, the adapter may
not supply the correct protocol (e.g., JMS) that the ESB expects. In
this case, the adapter would be Web Service enabled.
As complementary technologies in an ESB implementation (resource),
adapters and Web Services can work together to implement complex inte-
gration scenarios. Data synchronization (in addition to translation services)
is one of the primary objectives of resource adapters. Adapters can thus
take on the role of data synchronization and translation services, whereas
Web Services will enable application functions to interact with each other.
Web Services are an ideal mechanism for implementing a universally