Managing Information Access to an Enterprise Information System Using J2EE and Services Oriented Architecture

172 Managing Information Access to an EIS Using J2EE and Services Oriented Architecture

The two ways can coexist. In general, we have many legacy services and in

many cases one solution is not better than the other. These different ways to

provide the service are transparent to the client, who sees only the service

interface as described by WSDL.

In our integration scenario, we developed three different clients:

򐂰 J2EE Web application

This application can use the legacy service without the SOAP mediation. This

solution does not break the service-oriented architecture, because the legacy

service can be exposed as an enterprise service with bindings such as EJB,

JCA, or JMS. The client can even be deployed on the same application server

that hosts the connector.

򐂰 J2EE client

Although a J2EE client can use the traditional RMI/IIOP protocol, the Web

service approach has some benefits. The SOAP protocol is often easier to

configure with firewalls than IIOP. The service model promotes separation

between the service provider and the consumer. Finally, if you have different

types of clients, it is simpler to run and test one interface.

򐂰 Other SOAP client

In today’s computing environment, almost all programming languages have a

SOAP API. So, we can have access to our EIS virtually everywhere in the

enterprise.

7.3 Service-oriented architecture

To better comprehend Web services technology, we need to understand its place

in the more general service oriented architecture

(SOA). This section describes

the technology stack that supports the SOA. For a detailed description of SOA,

see 7.6, “Further information” on page 195.

Figure 7-3 on page 173 describes briefly the layers of the SOA abstraction.

Chapter 7. Using Web services 173

Figure 7-3 SOA stack

The Transport is the foundation layer for the Web services programming stack.

All Web services must be available over some network. The network is often

based on HTTP protocol, but other kinds of network protocols, such as the

Internet Inter-ORB Protocol (IIOP) or the message-oriented middleware (MOM),

such as WebSphere MQ, are also used.

On top of the Transport layer is a

Messaging layer that facilitates

communications between Web services and their clients. The Messaging layer

usually is based on SOAP. SOAP is a simple request-response protocol that is

based on XML, which defines how to invoke the operations of a service.

The

Description layer is simple but covers a key role. It describes the service

details to the clients. WSDL takes the form of XML documents for the

programming interface and for the location of Web services. Publication of a

service is really any action by the service provider that makes the WSDL

document available to a potential service requester. Sending the WSDL (or a

URL pointer to the WSDL) as an e-mail to a developer is considered to be

publishing. Publishing is also advertising the WSDL in a UDDI registry that can

be thought of as a reachable collector of WSDL. The UDDI registry acts as a

service search engine. The UDDI registry can be useful internally as a reference

for many developers, or it can be exposed externally to facilitate partner

integration.

The next layer is

Quality of Service. To be viable for e-business, Web services

must possess the same characteristics that business applications in an

enterprise must possess, including reliability, availability, manageability, security,