Enterprise Service Bus (ESB) - Guide to Cloud Computing for Business and Technology Managers - page 204

capabilities could be supported by emerging standard efforts such
as WS-Notification.
4. Transformation capabilities : A critical ability of the ESB is the ability
to route service interactions through a variety of transport proto-
cols and to transform from one protocol to another where necessary.
Another important aspect of an ESB implementation is the ability
to support service messaging models and data formats consistent
with the SOA interfaces. A major source of value in an ESB is that
it shields any individual component from any knowledge of the
implementation details of any other component. The ESB transfor-
mation services make it possible to ensure that messages and data
received by any component are in the format it expects, thereby
removing the need to make changes. The ESB plays a major role in
transforming between differing data formats and messaging mod-
els, whether between basic XML formats and Web Service messages
or between different XML formats (e.g., transforming an industry-
standard XML message to a proprietary or custom XML format).
The ESB connectivity and translation infrastructure is discussed in
Section 9.4.5 below.
5. Service enablement capabilities : Service enablement includes the abil-
ity to access already existing resources such as legacy systems—
technically obsolete mission-critical elements of an organization's
infrastructure—and includes them in an SOA implementation.
Tactically, legacy assets must be leveraged, service enabled, and inte-
grated with modern service technologies and applications.
6. Endpoint discovery with multiple QoS capabilities : The ESB should
support the basic SOA need to discover, locate, and bind to ser-
vices. As many network endpoints can implement the same service
contract, the ESB should make it possible for the client to select
the best endpoint at runtime, rather than hard-coding endpoints
at build time. The ESB should therefore be capable of supporting
various QoSs and allow clients to discover the best service instance
with which to interact based on QoS properties. Such capabilities
should be controlled by declarative policies associated with the
services involved using a policy standard such as the WS-Policy
framework.
7. Long-running process and transaction capabilities : Service orienta-
tion, as opposed to distributed object architectures such as .NET or
J2EE, more closely reflects real-world processes and relationships.
Hence, SOA represents a much more natural way to model and
build software that solves real-world business processing needs.
Accordingly, the ESB should provide the ability to support business
processes and long-running services—services that tend to run for
long duration, exchanging message (conversation) as they progress.