Information Technology Reference
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These tools enable the processing and management of XML documents.
Another advantage of XML is that it retains the data's structure in transit.
In addition, XML is very flexible, and this flexibility positions XML as the
most suitable standard for solving middleware and application heterogeneity
problems. XML also solves the data format problem mentioned previously.
A basic XML document consists of a top element. This top element may
consist of data (the payload), an attribute, and any number of other elements
in a recursive manner. A sample portion of a simple XML document is shown
in Listing 8.1. This document contains a top element named address, which
has a single attribute that is used to specify the country. This top element
has also four child elements, which provide information on the name of the
person, the street address, the city, and the postal code. Each of these child
elements has data (that is, a payload) contained in them. For example, the
data for the name element are Sachin Tendulkar .
Listing 8.1: Basic XML document structure
1 <address country = "India">
2 <name>Sachin Tendulkar</name>
3 <street>Dadar Gymkhana</street>
4 <city>Mumbai</city>
5 <state>Maharashtra</state>
6 <postal-code>45561</postal-code>
7 </address>
The grammar and structure of an XML type document is defined in a
schema. Another important concept used in XML is namespaces, which are
used to avoid the collision of names in different spaces and to extend the use
of vocabulary defined in one specific domain to other domains. The discus-
sion will include schemas, namespaces, and various models to use for XML
parsing, processing, creating, and editing.
8.3 WSDL
Web Services Description Language (WSDL) is an XML-based language for
describing the interface and other characteristics of a Web Service. This is the
second application of XML to solve the heterogeneity problems mentioned
earlier in this chapter. WSDL offers the following advantages in the descrip-
tion of the services as compared to previously described approaches:
• Unlike CORBA's IDL and RPC's specification files, WSDL is more
completely agnostic toward programming languages and middle-
ware technologies. This feature of WSDL is the direct result of it
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