Patterns: Implementing Self-Service in an SOA Environment

164 Patterns: Implementing Self-Service in an SOA Environment

򐂰 Web services architecture

򐂰 Web services design considerations

򐂰 The key challenges in Web services

򐂰 Best practices for Web services

7.3.1 Web services architecture

Web services are deployed on the Web by service providers. The functions

provided by the Web service are described using the Web Services Description

Language (WSDL). Deployed services are published on the Web by service

providers.

A

service broker helps service providers and service requestors find each other.

A service requestor uses the Universal Discovery Description and Integration

(UDDI) API to ask the service broker about the services it needs. When the

service broker returns the search results, the service requestor can use those

results to bind to a particular service.

As we can see in Figure 7-9:

򐂰 Web service descriptions can be created and published by service providers.

򐂰 Web services can be categorized and searched by specific service brokers.

򐂰 Web services can be located and invoked by service requesters.

Figure 7-9 Web services roles and operations

We can now look at the building blocks of Web services:

򐂰 SOAP

򐂰 UDDI

򐂰 WSDL

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Service

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SOAP

Chapter 7. Application and system design guidelines 165

SOAP

SOAP is a network-, transport-, and programming language-neutral protocol that

allows a client to call a remote service. The message format is XML. The

currently adopted standard is W3C’s SOAP 1.1 specification, while SOAP 1.2 is

in the review process.

SOAP has the following characteristics:

򐂰 SOAP is designed to be simple and extensible.

򐂰 All SOAP messages are encoded using XML.

򐂰 SOAP is transport protocol independent. HTTP is one of the supported

transports. Hence, SOAP can be run over an existing Internet infrastructure.

򐂰 There is no distributed garbage collection. Therefore, call by reference is not

supported by SOAP; a SOAP client does not hold any stateful references to

remote objects.

򐂰 SOAP is operating system independent and not tied to any programming

language or component technology. It is object model neutral.

Due to these characteristics, it does not matter what technology is used to

implement the client, as long as the client can issue XML messages. Similarly,

the service can be implemented in any language, as long as it can process XML

messages.

WSDL

The Web Services Description Language (WSDL) is an XML-based interface and

implementation description language. WSDL1.1 provides a notation to formally

describe both the service invocation interface and the service location.

WSDL allows a

service provider to specify the following characteristics of a Web

service:

򐂰 The name of the Web service and addressing information

򐂰 The protocol and encoding style to be used when accessing the public

operations of the Web service

򐂰 Type information, including operations, parameters, and data types

comprising the interface of the Web service, plus a name for the interface

A WSDL specification uses XML syntax, therefore, there is an XML schema for it.

UDDI

UDDI stands for Universal Description Discovery and Integration. UDDI is both a

client-side API and a SOAP-based server implementation that can be used to

store and retrieve information on service providers and Web services.