Xml For Dummies Chapter 15 Using Xml With Web Services

XML FOR DUMMIES
Book author: Lucinda Dykes and Ed Tittel
Slides Prepared by Cong Tan
Part V : XML Application Development
Chapter 15: Using XML with Web services.

Contents.
What’s up with Web Services?
A Web Services Architecture
Where Will Web Services Lead?

1. What’s up with Web Service.
In the Web services world, services customers—individuals, corporation, organizations, associations.
In this same world, service providers seek to advertise and promote their services so that service consumer can take a look at the wealth of resources and pass these services on to their customers.
Figure 15-1 illustrates how an e-mail client on the desktop sends and receive messages via mail servers on the Internet.

• A Web services model for e-mail(Hotmail, Yahoo! Mail, and other) take a different approach to e-mail access.
• Figure 15-2 shows how the Web services e-mail approach is different from the desktop client e-mail approach.
• You have to access a Web page and provide an account name and password to supply proof of identity before you can access stored data of the Web application service.

2. A Web Services Architecture.
The Web Services Architecture is divided into four layers.
Higher layers depend and build on the capabilities supplied at lower layers. Here’s the list:
Discovery is the part of Web services environment in which service providers can supply descriptions of the information and services that they have to offer.
Description is the part of Web services in which available services and information are described in detail, along with the mechanisms necessary for prospective service consumers and service providers to exchange information with one another.
Packaging/Extensionsis the part of Web services that handles issues related to managing, packaging, and securing exchanges of information between a service consumer and a service provider.
Transportis the part of Web services that implements protocols related to moving messages from a sender to a receiver.

2.1 Transport: Moving XML messages.
At Transport level — the bottom of the stack — software clients(like Web browsers) and service delivery software on Web servers communicate with each other.
Bottom line? The Transport layer acts like the highway that carries messages from senders to receivers.

2.1.1 SOAPing it up.
SOAP is independent of platform and language.
A SOAP message is an XML document that is sent via a transport protocol.
Underlying protocols in SOAP include not only the HTTP already used for everyday Web communications.
SOAP 1.2, also supports protocols in addition to HTTP, including SMTP and TCP/IP.

2.1.2 SOAP revisited(version 1.2).
SOAP 1.2 is a World Wide Web Consortium(W3C) Recommendation and consists of four basic parts:
An envelope that describes what’s in a message and how to process it
A set of encoding rules for application-defined data types
A convention for remote procedure calls(RPCs) and response
A binding convention for exchanging messages via an underlying protocol.
SOAP allows application to invoke object methods on remote servers.

2.2 Packaging/Extensions: Managing information exchange.
One layer up from the Transport layer in the Web Services Architecture is the Packaging/Extensions layer.
This layer is primarily concerned with establishing, managing, securing, and packaging information for exchange between service consumers and providers.
Packaging permits text information, images, and other kinds of binary data to be neatly encapsulated and sent to another party over a network.
Extensions address enhancements to basic messaging services for the following reasons:
To increase the level of security through encryption
To strengthen the credentials that establish consumer and provider identities.
To manage how messages are delivered from sender to receiver.
SOAP provides packaging and extensions for Web services by specifying a binding.

2.3 Description: Specifying services and related components.
The Description layer encompasses a number of XML applications designed to describe the following:
How services are composed
How services may be used
How services can interact with other services
How services must behave
What services can offer potential consumers
Many languages are available for Description layer services.
WSDL can provide a catalog of Yahoo!’s many services and the particulars of each of them.
WSDL is an XML format that describes the basic form of Web services requests with different network protocols.
It can be extended to any network protocol or messages format.
Each Web service includes a WSDL file that describes the bindings, methods, and data inputs and outputs.

2.4 Discovery: Finding What’s available.
At the top of the Web Services Architecture, you find XML applications geared to registering Web Services for discovery by searching for services, inquiring about specific services, or inspecting what services a particular service provider offers.
The major XML application used for discovery is UDDI.
UDDI enables businesses to discover one another, to define how they can interact, and to share service description in a global registry.
UDDI is a method for finding Web services.
UDDI is built upon SOAP and is independent of platform and implementation.
Three types of information are provided in a UDDI registry:
Contract and general business information(services, categories, URLS)
Information about Web services a business provides and how an application finds a particular service
Technical details and binding information.

3. Where Will Web Services Lead?
Those who build Web services applications must master the details of numerous XML languages, as well as know a scripting and/or programming language.
The discovery process enables you to find Web services providers.
If you want to check out some Web services, here are some Web sites of interest:
XMethods:Xmethods(www.xmethods.com) provides a list of publicy available Web services that you can try out.
SOAPMethods: Tony Hong of Xmethods has a UDDI browser with a sample repository ready for immediate access at www.soapclient.com/uddisearch.html.
Microsoft UDDI Registry: The Microsoft UDDI registry is free, but you must registry to use it at http://uddi.microsoft.com/default.aspx.
Web Services List: The Web Services List offers a list of over 1000 Web services. This is updated very frequently and can be accessed at www.webservicelist.com.

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