Web Services using WSDL and SOAP

Web Services using WSDL and SOAP

You can convert your applications into web-applications.

You can use XML to send messages between applications.


WSDL

WSDL is an XML-based language for describing Web services and how to access them.

WSDL describes a web service, along with the message format and protocol details for the web service.


SOAP

SOAP is a simple XML-based protocol that allows applications to exchange information over HTTP.

Or more simply: SOAP is a protocol for accessing a web service.

Web Services Platform Elements

Web Services have three basic platform elements: SOAP, WSDL and UDDI.

What is SOAP?
SOAP is a simple XML-based protocol to let applications exchange information over HTTP.
In simple: SOAP is a protocol for accessing a Web Service.

• SOAP stands for Simple Object Access Protocol
• SOAP is a communication protocol
• SOAP is a format for sending messages
• SOAP is designed to communicate via Internet
• SOAP is platform independent
• SOAP is language independent
• SOAP is based on XML
• SOAP is simple and extensible
• SOAP allows you to get around firewalls
• SOAP is a W3C standard

What is WSDL?
WSDL is an XML-based language for describing Web services and how to access them.

• WSDL stands for Web Services Description Language
• WSDL is based on XML
• WSDL is used to describe Web services
• WSDL is also used to locate Web services
• WSDL is a W3C standard

What is UDDI?
UDDI is a directory service where businesses can register and search for Web services.

• 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

Using Web Services

A few years ago Web services were not fast enough to be interesting.

Thanks to the major IT development the last few years, most people and companies have broadband connection and use the web more and more.

Interoperability has Highest Priority

When all major platforms could access the Web using Web browsers, different platforms could interact. For these platforms to work together, Web applications were developed.

Web-applications are simple applications run on the web. These are built around the Web browser standards and can mostly be used by any browser on any platform.

Web Services take Web-applications to the Next Level

Using Web services, your application can publish its function or message to the rest of the world.

Web services use XML to code and to decode data, and SOAP to transport it (using open protocols).

With Web services, your accounting department's Win 2k server's billing system can connect with your IT supplier's UNIX server.

Web Services have Two Types of Uses

Reusable application components.

There are things applications need very often. So why make these over and over again?

Web services can offer applications components like currency conversion, weather reports, or even language translation as services.

Ideally, there will be only one type of each application component, and anyone can use it in their application.

Connect existing software.

Web services help to solve the interoperability problem by giving different applications a way to link their data.

With Web services you can exchange data between different applications and different platforms.

Introduction to Web Services

Web Services can convert your applications into Web-applications.

Web Services are published, found, and used through the Web.

What are Web Services?

• Web services are application components
• Web services communicate using open protocols
• Web services are self-contained and self-describing
• Web services can be discovered using UDDI
• Web services can be used by other applications
• XML is the basis for Web services

The basic Web services platform is XML + HTTP.

The HTTP protocol is the most used Internet protocol.

XML provides a language which can be used between different platforms and programming languages and still express complex messages and functions.

Web services platform elements:

• SOAP (Simple Object Access Protocol)
• UDDI (Universal Description, Discovery and Integration)
• WSDL (Web Services Description Language)

The Future of Web services

The Web Services platform is a simple, interoperable, messaging framework. It still misses many important features like security and routing. But, these features will be available as soon as SOAP becomes more advanced.

Hopefully, Web services can make it much easier for applications to communicate.

What is Representational state transfer?

Finally, Representational State Transfer (REST) attempts to describe architectures which use HTTP or similar protocols by constraining the interface to a set of well-known, standard operations (like GET, POST, PUT, DELETE for HTTP). Here, the focus is on interacting with stateful resources, rather than messages or operations. An architecture based on REST (or is 'RESTful') can use WSDL to describe SOAP messaging over HTTP, which defines the operations, can be implemented as an abstraction purely on top of SOAP (e.g., WS-Transfer), or can be created without using SOAP at all.

WSDL version 2.0 offers support for binding to all the HTTP request methods (not only GET and POST as in version 1.1) so it enables a better implementation of RESTful Web services. However, support for this specification is still poor in software development kits, which often offer tools only for WSDL 1.1.

What is Service-oriented architecture?

Web services can also be used to implement an architecture according to Service-oriented architecture (SOA) concepts, where the basic unit of communication is a message, rather than an operation. This is often referred to as "message-oriented" services.

SOA Web services are supported by most major software vendors and industry analysts. Unlike RPC Web services, loose coupling is more likely, because the focus is on the "contract" that WSDL provides, rather than the underlying implementation details.

What is Remote procedure calls?

RPC Web services present a distributed function (or method) call interface that is familiar to many developers. Typically, the basic unit of RPC Web services is the WSDL operation.

The first Web services tools were focused on RPC, and as a result this style is widely deployed and supported. However, it is sometimes criticised for not being loosely coupled, because it was often implemented by mapping services directly to language-specific functions or method calls. Many vendors felt this approach to be a dead end, and pushed for RPC to be disallowed in the WS-I Basic Profile.

What is web service?

A 'Web service' (also Web Service) is defined by the W3C as "a software system designed to support interoperable machine-to-machine interaction over a network". Web services are frequently just Web APIs that can be accessed over a network, such as the Internet, and executed on a remote system hosting the requested services.

The W3C Web service definition encompasses many different systems, but in common usage the term refers to clients and servers that communicate over the HTTP protocol used on the Web. Such services tend to fall into one of two camps: Big Web Services and RESTful Web Services.

"Big Web Services" use XML messages that follow the SOAP standard and have been popular with traditional enterprise. In such systems, there is often a machine-readable description of the operations offered by the service written in the Web Services Description Language (WSDL). The latter is not a requirement of a SOAP endpoint, but it is a prerequisite for automated client-side code generation in many Java and .NET SOAP frameworks (frameworks such as Spring, Apache Axis2 and Apache CXF being notable exceptions). Some industry organizations, such as the WS-I, mandate both SOAP and WSDL in their definition of a Web service.

More recently, RESTful Web services have been regaining popularity, particularly with Internet companies. These also meet the W3C definition, and are often better integrated with HTTP than SOAP-based services. They do not require XML messages or WSDL service-API definitions.

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