Web Services - Enabling Semantic Web Services: The Web Service Modeling Ontology - page 39

RPC, such as Transactional RPC, Object Brokers, Remote Method Invo-
cation (RMI), Transaction Processing (TP) monitors, and message-oriented
middleware (MOM).
Comprehensive middleware architectures such as CORBA - introduced by
the Object Management Group (OMG) in the early 1990s - already allowed
for advanced features such as dynamic selection and binding of services. Unfor-
tunately, these architectures did not reach the expected degree of acceptance
that would be required to reach the actual goal of a standardized middleware
platform: effective, simple means of communication for distributed software
components catering for painless solution of integration problems within an
organization on the one hand and across enterprise boundaries on the other
hand.
The technologies which are nowadays subsumed under the term “Web
services” have several advantages compared with their predecessors. These
advantages are the reason for the wider acceptance of Web services and guar-
antee a higher probability of long-term success:

• Communication between Web services relies on widely accepted protocols

such as HTTP.

• SOAP [92] offers a protocol for message exchange between Web services,

where XML is used as a unified exchange format. The growing acceptance
of XML as a data interchange format and of related technologies consider-
ably eases the pain of establishing syntactic interoperability between Web
services.

• Similarly to RPC and CORBA, there exists a standardized interface de-

scription language, WSDL [27], which is currently gaining increasing ac-
ceptance.

• As opposed to a pervasive, complex infrastructure, which would solve all

the problems of the interplay of distributed applications at once, the “Web
services Technology Stack” consists of a modular family of standards, each
of which tackles certain subproblems.

• Finally, the “global players” seem to have come to an agreement that the

solution to interoperability problems cannot be found in dozens of pro-
prietary approaches; instead, their research and development departments
are jointly engaging in the development of standard recommendations in
international standardization bodies.

Summarizing, Web service technologies in the narrow sense build upon
four main components:

• An agreed transport protocol .

• A platform-independent message description format .

• A language for Web service interface description that describes which op-

erations, and with which messages a service can offer.

• A registry for publication and discovery of available services.