Introduction to WSDL
WSDL is an XML-based
language for describing Web services and how to access them.
What You Should Already Know
Before you continue you should have a basic understanding of the following:
- XML
- XML Namespaces
- XML Schema
What is WSDL?
- WSDL stands for Web Services Description Language
- WSDL is written in XML
- WSDL is an XML document
- WSDL is used to describe Web services
- WSDL is also used to locate Web services
- WSDL is a W3C recommendation
WSDL Describes Web Services
WSDL stands for Web Services Description Language.
WSDL is a document written in XML. The document describes a Web service. It specifies the location
of the service and
the operations (or methods) the service exposes.
WSDL is a W3C Recommendation
WSDL became a W3C Recommendation 26. June 2007.
A WSDL document is just a simple XML document.
It contains set of definitions to describe a web service.
The WSDL Document Structure
A WSDL document describes a web service using these major elements:
| Element | Description |
|---|
| <types> |
| A container for data type definitions used by the web service |
| <message> |
| A typed definition of the data being communicated |
| <portType> |
| A set of operations supported by one or more endpoints |
| <binding> |
| A protocol and data format specification for a particular port type |
The main structure of a WSDL document looks like this:
<definitions>
<types>
data type definitions........
</types>
<message>
definition of the data being communicated....
</message>
<portType>
set of operations......
</portType>
<binding>
protocol and data format specification....
</binding>
</definitions>
<types>
data type definitions........
</types>
<message>
definition of the data being communicated....
</message>
<portType>
set of operations......
</portType>
<binding>
protocol and data format specification....
</binding>
</definitions>
A WSDL document can also contain other elements, like extension
elements, and a service element that makes it possible to group together
the definitions of
several web services in one single WSDL document.
WSDL Ports
The <portType> element is the most important WSDL element.
It describes a web service, the operations that can be performed, and the messages that are involved.
The <portType> element can be compared to a function library (or a module, or a class)
in a traditional programming language.
WSDL Messages
The <message> element defines the data elements of an operation.
Each message can consist of one or more parts. The parts can be compared
to the parameters of a function call in a traditional programming language.
WSDL Types
The <types> element defines the data types that are used by the web service.
For maximum platform neutrality, WSDL uses XML Schema syntax to define data types.
WSDL Bindings
The <binding> element defines the data format and protocol for each port
type.
WSDL Example
This is a simplified fraction of a WSDL document:
<message name="getTermRequest">
<part name="term" type="xs:string"/>
</message>
<message name="getTermResponse">
<part name="value" type="xs:string"/>
</message>
<portType name="glossaryTerms">
<operation name="getTerm">
<input message="getTermRequest"/>
<output message="getTermResponse"/>
</operation>
</portType>
<part name="term" type="xs:string"/>
</message>
<message name="getTermResponse">
<part name="value" type="xs:string"/>
</message>
<portType name="glossaryTerms">
<operation name="getTerm">
<input message="getTermRequest"/>
<output message="getTermResponse"/>
</operation>
</portType>
In this example the <portType> element defines "glossaryTerms"
as the name of a port, and "getTerm" as the name of an operation.
The "getTerm" operation has an input message called "getTermRequest"
and an output message called "getTermResponse".
The <message> elements define the parts of each message and
the associated data types.
Compared to traditional programming, glossaryTerms is a function library, "getTerm"
is a function with "getTermRequest" as the input parameter, and getTermResponse as
the return parameter.
The <portType> element is the most important WSDL element.
WSDL - The <portType> Element
The <portType> element defines a web service, the operations that can be performed, and the messages that are involved.
<portType> defines the connection point to a web service. It
can be compared to a function library (or a module, or a class)
in a traditional programming language. Each operation can be compared to
a function in a traditional programming language.
Operation Types
The request-response type is the most common operation type, but WSDL defines four types:
| Type | Definition |
|---|
| One-way |
| The operation can receive a message but will not return a response |
| Request-response |
| The operation can receive a request and will return a response |
| Solicit-response |
| The operation can send a request and will wait for a response |
| Notification |
| The operation can send a message but will not wait for a response |
One-Way Operation
A one-way operation example:
<message name="newTermValues">
<part name="term" type="xs:string"/>
<part name="value" type="xs:string"/>
</message>
<portType name="glossaryTerms">
<operation name="setTerm">
<input name="newTerm" message="newTermValues"/>
</operation>
</portType >
<part name="term" type="xs:string"/>
<part name="value" type="xs:string"/>
</message>
<portType name="glossaryTerms">
<operation name="setTerm">
<input name="newTerm" message="newTermValues"/>
</operation>
</portType >
In the example above, the portType "glossaryTerms" defines a one-way operation called "setTerm".
The "setTerm" operation allows input of new glossary terms messages using a "newTermValues"
message with the input parameters "term" and "value". However, no output is
defined for the operation.
Request-Response Operation
A request-response operation example:
<message name="getTermRequest">
<part name="term" type="xs:string"/>
</message>
<message name="getTermResponse">
<part name="value" type="xs:string"/>
</message>
<portType name="glossaryTerms">
<operation name="getTerm">
<input message="getTermRequest"/>
<output message="getTermResponse"/>
</operation>
</portType>
<part name="term" type="xs:string"/>
</message>
<message name="getTermResponse">
<part name="value" type="xs:string"/>
</message>
<portType name="glossaryTerms">
<operation name="getTerm">
<input message="getTermRequest"/>
<output message="getTermResponse"/>
</operation>
</portType>
In the example above, the portType "glossaryTerms" defines a request-response operation called "getTerm".
The "getTerm" operation requires an input message called "getTermRequest"
with a parameter called "term", and will return an output message called "getTermResponse"
with a parameter called "value".
WSDL bindings defines the message format and protocol details for a web service.
Binding to SOAP
A request-response operation example:
<message name="getTermRequest">
<part name="term" type="xs:string"/>
</message>
<message name="getTermResponse">
<part name="value" type="xs:string"/>
</message>
<portType name="glossaryTerms">
<operation name="getTerm">
<input message="getTermRequest"/>
<output message="getTermResponse"/>
</operation>
</portType>
<binding type="glossaryTerms" name="b1">
<soap:binding style="document"
transport="http://schemas.xmlsoap.org/soap/http" />
<operation>
<soap:operation soapAction="http://example.com/getTerm"/>
<input><soap:body use="literal"/></input>
<output><soap:body use="literal"/></output>
</operation>
</binding>
<part name="term" type="xs:string"/>
</message>
<message name="getTermResponse">
<part name="value" type="xs:string"/>
</message>
<portType name="glossaryTerms">
<operation name="getTerm">
<input message="getTermRequest"/>
<output message="getTermResponse"/>
</operation>
</portType>
<binding type="glossaryTerms" name="b1">
<soap:binding style="document"
transport="http://schemas.xmlsoap.org/soap/http" />
<operation>
<soap:operation soapAction="http://example.com/getTerm"/>
<input><soap:body use="literal"/></input>
<output><soap:body use="literal"/></output>
</operation>
</binding>
The binding element has two attributes - name and type.
The name attribute (you can use any name you want) defines the name of the
binding, and the type attribute points to the port for the binding, in this case the "glossaryTerms" port.
The soap:binding element has two attributes - style and transport.
The style attribute can be "rpc" or "document". In this case we use
document. The transport attribute defines the SOAP protocol to use.
In this case we use HTTP.
The operation element defines each operation that the portType exposes.
For each operation the corresponding SOAP action has to be defined. You must
also specify how the input and output are encoded. In this case we use "literal".
Universal Description, Discovery and Integration (UDDI)
is a directory service where businesses can register and search for Web
services.
What is UDDI
UDDI is a platform-independent framework for describing services,
discovering businesses, and integrating business services by using the
Internet.
- UDDI stands for Universal Description, Discovery and Integration
- UDDI is a directory for storing information about web services
- UDDI is a directory of web service interfaces described by WSDL
- UDDI communicates via SOAP
- UDDI is built into the Microsoft .NET platform
What is UDDI Based On?
UDDI uses World Wide Web Consortium (W3C) and Internet Engineering
Task Force (IETF) Internet standards such as XML, HTTP, and DNS
protocols.
UDDI uses WSDL to describe interfaces to web services
Additionally, cross platform programming features are addressed by adopting
SOAP, known as XML Protocol messaging specifications found at the W3C Web site.
UDDI Benefits
Any industry or businesses of all sizes can benefit from UDDI.
Before UDDI, there was no Internet standard for businesses to reach their customers and partners with information about their
products and services. Nor was there a method of how to integrate into each other's systems and processes.
Problems the UDDI specification can help to solve:
- Making it possible to discover the right business from the millions currently online
- Defining how to enable commerce once the preferred business is discovered
- Reaching new customers and increasing access to current customers
- Expanding offerings and extending market reach
- Solving customer-driven need to remove barriers to allow for rapid participation in the global Internet economy
- Describing services and business processes programmatically in a single, open, and secure environment
How can UDDI be Used
If the industry published an UDDI standard for flight rate
checking and reservation, airlines could register their services into an UDDI
directory. Travel agencies could then search the UDDI directory to find the
airline's reservation interface. When the interface is found, the travel agency
can communicate with the service immediately because it uses a well-defined
reservation interface.
Who is Supporting UDDI?
UDDI is a cross-industry effort driven by all major platform and software
providers like Dell, Fujitsu, HP, Hitachi, IBM, Intel, Microsoft, Oracle, SAP,
and Sun, as well as a large community of marketplace operators, and e-business
leaders.
Over 220 companies are members of the UDDI community.
No comments:
Post a Comment