Page 221 - DCAP312_WEB_TECHNOLOGIES_II

Unit 10: Web Services

The W3C also states, “We can identify two major classes of Web services, REST-compliant Web Notes
services, in which the primary purpose of the service is to manipulate XML representations
of Web resources using a uniform set of “stateless” operations; and arbitrary Web services, in
which the service may expose an arbitrary set of operations
SOAP Webservices provide a simple way of providing public information in websites. Directories,
maps, translations, searches and zip code/postcode lookup all suddenly become quick and easy
to implement, especially in .NET. Windows Live Webservice has now joined the market with a
whole range of services which are likely to change the way we use the Web.
A simple XML Web service using ASP.NET is relatively easy and is covered in Building XML Web
Services Using ASP.NET Basics. However, the true power of XML Web services is realized when
you look at the infrastructure. XML Web services are built on top of the .NET Framework and
the common language runtime. An XML Web service can take advantage of these technologies.
For instance, the performance, state management, and authentication supported by ASP.NET
can all be taken advantage of by building XML Web services using ASP.NET.
The infrastructure for XML Web services is built to conform to industry standards such as
SOAP, XML, and WSDL, and this allows clients from other platforms to interoperate with XML
Web services. As long as a client can send standards-compliant SOAP messages, formatted
according to a service description, that client can call an XML Web service created using ASP.NET
(regardless of the platform on which the client resides). When you build an XML Web service
using ASP.NET, it automatically supports clients communicating using the SOAP, HTTP-GET,
and HTTP-POST protocols. Since HTTP-GET and HTTP-POST support passing messages in
URL-encoded name-value pairs, the data type support for these two protocols is not as rich as
that supported for SOAP. In SOAP, which passes data to and from the XML Web service using
XML, you can define complex data types using XSD schemas, which support a richer set of
data types. Developers building an XML Web service using ASP.NET do not have to explicitly
define complex data types they expect using an XSD schema. Rather, they can simply build a
managed class. ASP.NET handles mapping class definitions to an XSD schema and mapping
object instances to XML data in order to pass it back and forth across a network.
Why use Web Services
The major reasons for using Web services are to gain:

1. Interoperability among distributed applications that span diverse hardware and software
platforms.

2. Accessibility of applications through firewalls using Web protocols.
3. Across-platform, cross-language data model (XML) that facilitates developing heterogeneous
distributed applications.
Because Web services are accessed using standard Web protocols, such as XML and HTTP, the
diverse and heterogeneous applications on the Web (which typically already understand XML
and HTTP) can automatically access Web services, solving the ever-present problem of how
different systems communicate with each other. These different systems might be Microsoft
SOAP Toolkits clients, J2EE applications, legacy applications, and so on. These systems might
be written in a variety of programming languages, such as Java, C++, or Perl. As long as the
application that provides the functionality is packaged as a Web service each of these systems
can communicate with any other.
Web Services represent a new standard-based and simplified model for creating and connecting
distributed applications across the web in the form of services. Web Services are built on the top
of existing and widely adopted Internet protocols such as HTTP, XML, TCP/IP , HTML , Java
and XML . This means the base foundation for building the Web Services is already in place.

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