The .NET platform requires XML梥pecifically XML Web Services梩o achieve its
vision of applications communicating seamlessly across disparate networks,
hardware, and software. XML Web Services enable applications to communicate
and share data over the Internet, regardless of operating system or
programming language. XML Web Services are not complex. In fact, it's their
simplicity that makes them so powerful. They are no more than XML text
messages passing back and forth between computers via the same network or
across the Internet.
The key to making XML Web Services work is to agree to a simple data
description format梐nd that format is XML. Specifically, XML Web Services
use XML for three things:
Wire format: SOAP. At the lowest level, systems need to speak the same
language. In particular, communicating applications need to have a set of
rules for how they are going to represent different data types (such as
integers and arrays) and how they are going to represent commands (that is,
what should be done with the data). Also, the applications need a way to
extend this language if they have to. The Simple Object Access Protocol
(SOAP), now on its way to becoming a W3C standard, is a common set of rules
about how data and commands will be represented and extended.
Description: Web Services Description Language. Once applications have
general rules for how they will represent data types and commands, they
need a way to describe the specific data and commands they accept. It's not
enough for an application to say that it accepts integers; somehow, there
must be a way to deterministically say that, if you give it two integers,
it will multiply them. The Web Services Description Language (WSDL), also
working its way through W3C standardization, is an XML grammar that
developers and development tools can use to represent the capabilities of
an XML Web Service.
Discovery: UDDI. The final layer needed is a set of rules for how to locate
a service's description梬here does a human or tool look by default to
discover a service's capabilities? The Universal Description, Discovery,
and Integration (UDDI) specification provides a set of rules so that a
human or development tool can automatically discover a service's WSDL
description.
Once these three layers are in place, a developer can easily find an XML
Web Service, instantiate it as an object, integrate it into an application,
and build enough infrastructure so that the resulting application can
easily use this XML Web Service.