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Standards
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So much of the promise of Web Services depends on broad interoperability
between applications. Therefore, the make/break lies in the evolution
of technology standards and much of the work today is in this arena.
A brief summary of the technology is presented here and a detailed
discussion can be found in Appendix A.
In the early days of the Web, core technologies were used to provide
an interface to distributed services (e.g., HTML forms calling CGI
scripts). XML has accelerated this development, and has sparked
the emergence of numerous XML-based environments that enable Web
Services. These environments are starting to encompass the classical
components of distributed application environments, such as standard
protocol conventions, security mechanisms, processes to ensure reliable
delivery and provide transaction functionality, and interface description
languages, all of which are adapted to the special needs of the
Web environment, and the requirements of XML.
There are a few key standard specifications and technologies involved
when building or consuming Web Services. The goal of these technologies
is to define:
- A standard way to represent data
- A common, extensible, message format
- A common, extensible, service description language
- A way to discover services located on a particular Web site
- A way to discover service providers
The 'official' source for defining the standards used for Web Services
is the World Wide Web Consortium (W3C). It develops interoperable
technologies such as specifications, guidelines, software, and tools
and serves as a forum for information, commerce, communication,
and collective understanding.
The industry is attempting to take advantage of accepted W3C standards
such as XML, HTTP, and DNS protocols to define and agree on a Web
Service platform. The basic data representation and translation
platform is XML plus HTTP. HTTP is a ubiquitous protocol, running
practically everywhere on the Internet. XML provides a metalanguage
in which you can write specialized languages to express complex
interactions between clients and services or between components
of a service. The XML message is converted to a middleware request
and the result is converted back to XML. DNS is the standard protocol
for mapping the service delivery to deliver the message to a unique
address on a server.
XML is the industry choice for a standard way to represent data.
Most Web Service-related specifications use XML for data representation
and XML schemas to describe data types. XML is a great foundation;
it enables flexible encoding of almost any kind of structured data
in a way that doesn't mandate any particular language or operating
environment. But, unless both the sender and receiver of the XML
message speak the same language or set the same translation requirements,
interoperability between applications is difficult. XML protocols
are very effective and offer a simple model for inter-application
communication, but unless the applications involved know how to
talk to each other, their ultimate value is limited. At a minimum,
applications must know:
- How to find each other
- What sorts of messages are expected by the other side
- What kinds of transport protocols are in use
- How to provide the necessary information
To create 'true' Web Services, this basic capability needs to be
augmented with a few other technologies, while maintaining the ubiquity
and simplicity of the Web. The 'true' Web Services platform can
be thought of as XML plus HTTP plus SOAP plus WSDL plus UDDI.
SOAP means Simple Object Access Protocol. It is used to encode
messages such as remote procedure calls (RPC) for request-response
messages. WSDL means Web Services Description Language and is used
to describe a Web Service interface. In essence, SOAP and WSDL facilitate
distributed computing. SOAP provides a simple distributed computing
mechanism that can be used over multiple transports. It also defines
a way to perform RPCs using HTTP as the underlying communication
protocol.
UDDI means Universal Description, Discovery and Integration service.
It specifies a mechanism for Web Service providers to advertise
the existence of their services and for Web Service consumers to
locate services of interest. Using a UDDI interface, businesses
can dynamically connect internal applications and services provided
by external business partners.
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Barbara Angius Saxby (barbara@accelentmarketing.com)
founded Accelent (www.accelentmarketing.com)
to help software startups accelerate marketing strategies, planning,
and execution. She specializes in positioning and launching enterprise
infrastructure and application companies. Barbara is a senior marketing
executive with over 20 years experience in strategic marketing management
and has done extensive work internationally.
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