Oracle Application Server 10g Essentials [Electronic resources] نسخه متنی

Chapter 11. Web Services

Web Services are functions or
procedures that are accessible to other computer programs over a
network, using a standard transport protocol and encoding. Typically,
the transport protocol used is HTTP, the encoding is
XML-RPC or SOAP, and
the messages communicated between programs are exchanged as XML
documents.

Web Services are all about interoperability. By encapsulating
programming language-specific function or procedure call syntax into
a standardized XML document syntax, Web Services allow any program
deployed on any operating system to utilize a candidate function or
procedure exposed as a Web Service.

Exposing program functions or procedures to be called remotely
isn't a new idea. Database


stored procedures and EJBs are two
longstanding examples of remote procedure calls.
What's new with Web Services is the level of
interoperability built into them.

To call a database stored procedure, you must use a proprietary or
standardized API such as JDBC. However, such APIs allow your program
to call only functions or procedures that exist in a target database.
These APIs also require a proprietary network protocol.
Corporate
firewalls typically
don't allow proprietary protocols to pass through
them, so their use can limit the level of interoperability.

To call an EJB, you can either use the EJB API or CORBA, but this
solution allows only an Enterprise Java program, or a program written
with a programming language that uses a CORBA API, to use the target
EJB. Once again, a network protocol, RMI, is used that may not be
supported by a corporate firewall.

In contrast, Web Services allow any programming language on any
operating system in which a Web Services client implementation exists
to call a target Web Service. In addition, the use of
HTTP as a transport protocol, which
is generally supported by all firewalls, allows easy access to Web
Services.

Of course, this highly interoperable, lowest-common-denominator
approach comes with a price: slower

performance. Web Services as remote
procedure calls are significantly slower than database stored
procedures or EJBs. This is understandable because extra steps are
involved:

Encoding a remote procedure call into the XML document on the
client-side

Parsing the XML document to call the desired function on the
server-side

Encoding the result into an XML document on the server-side

Parsing the XML document to retrieve the desired result on the
client-side

Regardless, Web Services are an ideal solution when it comes to
integrating heterogeneous computer applications.

This chapter begins by taking a brief look at the architecture used
by Web Services. Next, it covers the commonly used protocols and
standards used for Web Services, highlighting Oracle Application
Server's support for each. It finishes up by
examining Oracle Application Server's implementation
of Web Services, including programming and management tools.