21.1 What are Web Services

Web services is the term for a technology that consists of a set of messaging protocols and programming standards that expose business functions over the Internet using open XML-based standards, and an individual web service is a discrete, reusable software component that is accessed programmatically over the Internet, using HTTP or sometimes SMTP, to return a response.

Web services allow enterprises to expose business functionality irrespective of the platform or language of the originating application because the business functionality is exposed in such a way that it is abstracted to a message composed of standard XML constructs that can be recognized and used by other applications.

Oracle ADF has built in support to use web services as business service providers in applications. For example, an application could:

Use some functionality in an application run by another company and exposed as a web service to provide business-to-business e-commerce.
Use web service made available through a site such as Xmethods.com to provide some standard functionality.
Find a web service that provides the specified functionality in a UDDI registry and use it at runtime.

You can use Oracle ADF to build applications that target one or all of the tiers in the J2EE platform using your choice of implementation technologies. Using ADF business components to implement your business services, you gain the additional flexibility to be able to expose parts of your application as web services at any time without code changes.

Factors influencing the decision to deploy a component as a web service are:

Web services separate the application from the underlying architecture.
Web services are lightweight, which can result in improved performance across the Internet or an intranet.
Web services technology is designed to use the Web infrastructure, including HTTP.

It is useful to describe the XML standards on which web services are based.

21.1.1 SOAP

The Simple Object Access Protocol (SOAP) is a lightweight XML-based protocol that is used for the sending and receiving over messages of a transport protocol, usually HTTP or SMTP. The SOAP specification, which you can see at website of the World Wide Web Consortium, provides a standard way to encode requests and responses. It describes the structure and data types of message payloads using XML Schema.

A SOAP message is constructed of the following components:

A SOAP envelope that contains the SOAP body, the important part of the SOAP message, and optionally a SOAP header.
A protocol binding that specifies how the SOAP envelope is sent, that in the case of web services generated in JDeveloper, is via HTTP.

Web services use SOAP, the XML protocol for expressing data as XML and transporting it across the Internet using HTTP, and SOAP allows for more than one way of converting data to XML and back again. JDeveloper supports SOAP RPC encoding, SOAP RPC-literal style, and document-literal style (also known as message style).

The web services you create in JDeveloper can be either for deployment on Oracle SOAP, which is based on Apache SOAP 2.2 and is part of the Oracle Application Server (OracleAS), or to the SOAP server, which is one of the OC4J containers in OracleAS.

21.1.2 WSDL

The Web Services Description Language (WSDL) is an XML language used to describe the syntax of web service interfaces and their locations. You can see the WSDL v1.1 specification at the website of the World Wide Web Consortium. Each web service has a WSDL document that contains all the information needed to use the service, the location of the service, its name, and information about the methods that the web service exposes. When you use one of JDeveloper's web service publishing wizards to produce your web service, the WSDL document for your service is automatically generated.

21.1.3 UDDI

Universal Description, Discovery and Integration (UDDI) provide a standards-based way of locating web services either by name, or by industry category. UDDI registries can be public, for example the public UDDI registries that are automatically available from JDeveloper, or private, such as a UDDI registry used within an organization. This version of JDeveloper only supports web service discovery using UDDI, however future versions will provide full support for UDDI registration. You can see the UDDI v2 specification at http://www.uddi.org/.

JDeveloper's UDDI browser, in the Connections Navigator, stores information about a UDDI registry and allows you to search a UDDI registry using search criteria that you specify to find web services that are described by WSDLs.

You can create your own registry connections to another public UDDI registry, or to a private UDDI registry within your organization. This creates a connection descriptor properties file that contains the enquiry endpoint and the business keys of the registry. You can find this file at <jdev_install>/system<release_and_build_number>/uddiconnections.xml, where <jdev_install> is the root directory in which JDeveloper is installed.

JDeveloper's Find Web Service wizard browses UDDI registries to find web services by either name or category. You must have an appropriate connection from your machine so that JDeveloper can make a connection to the UDDI registry you select, for example, a connection to the internet if you want to search a public UDDI registry, and you can only generate a stub to a web service that has a tick in the Is WSDL? column that identifies the registry entry as being defined by a WSDL document.

When you use UDDI registries a term you will come across, and that you may be unfamiliar with, is tModel, short for Technical Model. This represents the technical specification of a web service, and when you search for a web service using the Find Web Service wizard, the wizard also displays other web services that are compatible with the same tModel.

The data structure types used in UDDI are:

Service Details This section gives information about the service, including the name.
Business Entity This is the top-level data structure called businessEntity that contains information about the business providing the web service.
Service Bindings contains the bindingTemplate, that contains information about the service access point, and the tModel that gives the technical specification of the web service.

When the Find Web Services wizard finds a web service, it lists all web services that are compatible with the same tModel.

21.1.4 Web Services Interoperability

A key issue facing web services is how interoperable web services actually are. The key feature of web services is that they use common standards to avoid the problems that earlier solutions to getting different applications to be able to use each other's components, for example CORBA, had. However the standards themselves have been being written at the same time as the organizations have been starting to write, deploy and use web services. This has led to interoperability issues such as web services being written using different standards, for example, not using WSDL to provide web service information.

The Web Services-Interoperability Organization (WS-I) was formed by Oracle and other industry leaders to address these issues of interoperability, and to provide tools so that web services can be tested to see how well they interoperate. JDeveloper helps you to test the interoperability of web services by analyzing a web service for conformity to the WS-I Basic Profile 1.0. First you have to download a WS-I compliant analyzer. There are a number of these available from independent vendors, and one from the WS-I website. A set of test assertions is used to find out how well a web service conforms to the basic profile, and information is recorded for the following artifacts:

Discovery when a web service has been found using a UDDI registry. If the service has not been found using the Find Web Services wizard, this section of the report returns errors in the Missing Input section.
Description of a web service's WSDL document, where the different elements of the document are examined and non-conformities are reported. An example of a failure in this section is a failure of assertion WSI2703, that gives the message "WSDL definition does not conform to the schema located at http://schemas.xmlsoap.org/wsdl/soap/2003-02-11.xsd for some element using the WSDL-SOAP binding namespace, or does not conform to the schema located at http://schemas.xmlsoap.org/wsdl/2003-02-11.xsd for some element using the WSDL namespace."
Message that tests the request and response messages when the connection is made to the web service and it sends its reply.

For more information about WS-I including the specification, see the website of The Web Services-Interoperability Organization (WS-I) at ws-i.org.