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Chapter 8. WebSphere and XML approaches 165
there a mapping between Java and XML data types must be provided for. The
Apache SOAP run-time environment allows the developer to map between Java
and XML data types for an encoding style. The designer can specify a serializer
to marshal the Java type to XML, a deserializer to unmarshall the XML type to
Java, or both for two-way mapping.
The rules for mapping between Java and XML data types are stored in a SOAP
mapping registry object that is used by either the Java client proxy or the Web
service. The SOAP mapping registry has predefined rules for mapping between
simple Java and XML types. For complex XML types, it is up to the developer to
specify the mapping. The best way to map is to use the org.w3c.dom.Element.
This represents a generic XML element in the Document Object Model (DOM).
8.2 Web services
A Web service is a collection of functions that are packaged as a single entity
and published to the network for use by other programs. Web services are
building blocks for creating open distributed systems, and allow companies and
individuals to quickly and cheaply make their digital assets available worldwide.
Some examples of Web services are:
A credit checking service that returns credit information when given a
person’s identification number.
A stock quote service that returns the sock price associated with a specified
ticker symbol.
A purchasing service that allows computer systems to buy office supplies
when given an item code and a quantity.
A Web service can aggregate other Web services to provide a higher-level set of
features. For example, a Web service could provide a set of high-level features by
orchestrating lower-level Web services for car rental, air travel, and hotels.
Applications of the future will be built from Web services that are dynamically
selected at runtime based on their cost, quality, and availability.
Web services are pretty much guaranteed to be at the heart of the next
generation of distributed systems. The reasons are:
Interoperability:
Any Web service can interact with any other Web Service.The
Simple Object Access Protocol (SOAP), the new standard protocol by all of
the major vendors (and most of the minor ones), the agonies of converting
between CORBA, DCOM and other protocols should be over. And because
Web services can be written un any language, developers do not need to
change their developed environments in order to produce or consume Web
services.