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Chapter 5 IT Infrastructure and Emerging Technologies 221

WEB SERVICES AND SERVICE-ORIENTED
ARCHITECTURE

Web services refer to a set of loosely coupled software components that
exchange information with each other using universal Web communication
standards and languages. They can exchange information between two differ-
ent systems regardless of the operating systems or programming languages
on which the systems are based. They can be used to build open standard
Web-based applications linking systems of two different organizations, and they
can also be used to create applications that link disparate systems within a single
company. Web services are not tied to any one operating system or program-
ming language, and different applications can use them to communicate with
each other in a standard way without time-consuming custom coding.
The foundation technology for Web services is XML, which stands for Extensible
Markup Language. This language was developed in 1996 by the World Wide Web
Consortium (W3C, the international body that oversees the development of the
Web) as a more powerful and flexible markup language than hypertext markup
language (HTML) for Web pages. Whereas HTML is limited to describing how data
should be presented in the form of Web pages, XML can perform presentation,
communication, and storage of data. In XML, a number is not simply a number;
the XML tag specifies whether the number represents a price, a date, or a ZIP
code. Table 5.2 illustrates some sample XML statements.
By tagging selected elements of the content of documents for their mean-
ings, XML makes it possible for computers to manipulate and interpret their
data automatically and perform operations on the data without human inter-
vention. Web browsers and computer programs, such as order processing or
enterprise resource planning (ERP) software, can follow programmed rules
for applying and displaying the data. XML provides a standard format for data
exchange, enabling Web services to pass data from one process to another.
Web services communicate through XML messages over standard Web
protocols. Companies discover and locate Web services through a direc-
tory much as they would locate services in the Yellow Pages of a telephone
book. Using Web protocols, a software application can connect freely to other
applications without custom programming for each different application
with which it wants to communicate. Everyone shares the same standards.
The collection of Web services that are used to build a firm’s software sys-
tems constitutes what is known as a service-oriented architecture. A service-
oriented architecture (SOA) is set of self-contained services that commu-
nicate with each other to create a working software application. Business
tasks are accomplished by executing a series of these services. Software

TABLE 5.2 EXAMPLES OF XML
PLAIN ENGLISH XML
Subcompact <AUTOMOBILETYPE=”Subcompact”>
4 passenger <PASSENGERUNIT=”PASS”>4</PASSENGER>

$16,800 <PRICE CURRENCY=”USD”>$16,800</PRICE>

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