Section 3.1. Scope of the Architecture

3.1. Scope of the Architecture

The high-level schematic introduced in Chapter 1 (Figure 1-7) illustrates a layered view of the important foundational capabilities that are required of SOA. This chapter introduces a specific rendering of this conceptual framework with a particular collection of Web services specifications that are based on and extend basic Internet standards that were described in Chapter 2, "Background." Note that specifications used in this rendering are those that IBM has developed in a collaborative effort with other industry partners, most notably Microsoft. The description in this chapter is intended to give a high-level "fly by" only, with the express purpose of providing an overall summary perspective. The following chapters of this book discuss these Web services specifications in much greater detail.

Web services had its beginnings in mid to late 2000 with the introduction of the first version of XML messagingSOAP, WSDL 1.1, and an initial version of UDDI as a service registry. This basic set of standards has begun to provide an accepted industry-wide basis for interoperability among software components (Web services) that is independent of network location, in addition to specific implementation details of both the services and their supporting deployment infrastructure. Several key software vendors have provided these implementations, which have already been widely used to address some important business problems.

Although the value of Web services technology has been demonstrated in practice, there is a desire to use the approach to address more difficult problems. Developers are looking for enhancements that raise the level and scope of interoperability beyond the basic message exchange, requiring support for interoperation of higher-level infrastructure services. Most commercial applications today are built assuming a specific programming model. They are deployed on platforms (operating systems and middleware) that provide infrastructure services in support of that programming model, hiding complexity, and simplifying the problems that the solution developer has to deal with. For example, middleware typically provides support for transactions, security, or reliable exchange of messages (such as guaranteed, once-only delivery). On the other hand, there is no universally agreed standard middleware, which makes it difficult to construct applications from components that are built using different programming models (such as Microsoft COM, OMG CORBA, or Java 2 Platform, Enterprise Edition (J2EE) Enterprise Java Beans). They bring with them different assumptions about infrastructure services that are required, such as transactions and security. As a consequence, interoperability across distributed heterogeneous platforms (such as .NET and J2EE) presents a difficult problem.

The Web services community has done significant work to address this interoperability issue, and since the introduction of the first Web services, various organizations have introduced other Web servicesrelated specifications. Figure 3-1 illustrates a population of the overall SOA stack shown in Figure 1-7 with current standards and emerging Web services specifications that IBM, Microsoft, and other significant IT companies have developed. The remainder of this chapter provides a high-level introduction to these Web services specifications that realize more concretely the capabilities that are described in the SOA framework in Chapter 1 and that extend the earlier Web services technology of XML, SOAP, and WSDL to provide secure, reliable, and transacted interoperability. The specifications define formats and protocols that allow services to interoperate across those vendor platforms that provide conformant implementations, either natively or by mapping them onto existing proprietary middleware offerings.

Figure 3-1. Web services architecture.

 <definitions targetNamespace="...">        <!-- WSDL definitions in this document -->        <!-- referenced using "tns" prefix -->          <types>           <!-- XSD definitions for this service -->           <!-- referenced using "xsd1" prefix -->           <xsd:schema>              <xsd:import namespace="http://www.purchase.com/xsd/svp-svc">           </xsd:schema>        </types>        <message name="purchaseResponse">           <part name="purchaseResponse" element="xsd1:PurchaseStatus"/>        </message>        <message name="purchaseRequest">           <part name="purchaseRequest" element="xsd1:PurchaseRequest"/>        </message>        <message name="ServicePacValidationInput">           <part name="spvDataInput"                  element="xsd1:ServicePacValidationData"/>        </message>        <message name="ServicePacValidationOutput">           <part name="spvDataOutput"                  element="xsd1:ServicePacValidationData"/>        </message>        <portType name="spvPortType">           <operation name="purchaseServicePacs">              <input name="purchaseInput" message="tns:purchaseRequest"/>              <output name="purchaseOutput"                       message="tns:purchaseResponse"/>           </operation>           <operation name="validateServicePac">              <input name="Input"                      message="tns:ServicePacValidationInput"/>              <output name="Output"                       message="tns:ServicePacValidationOutput"/>           </operation>        </portType>        <binding name="spvBinding" type="tns:spvPortType">           <wsp:PolicyReference              URI="http://www.purchase.com/policies/DSig">           <soap:binding style="document"   transport="http://schemas.xmlsoap.org/soap/http"/>           <operation name="purchaseServicePacs">             <wsp:PolicyReference URI=               "http://www.purchase.com/policies/Encrypt">             <soap:operation soapAction=     "http://www.purchase.com/spvPortType/purchaseServicePacsRequest"/>           </operation>           <operation name="validateServicePac">                <soap:operation soapAction= "http://www.purchase.com/spvPortType/validateServicePacRequest"/>           </operation>       </binding>       <service name="spv-svc">          <port name="spv-svc-port" binding="tns:spvBinding">             <soap:address location="http://www.purchase.com/spv"/>          </port>       </service>    </definitions>