Web Services Inspection Language

Discovery mechanisms are another extremely important topic for P2P technologies, and a great candidate for convergence with general Web services technologies. As seen in Chapter 11, UDDI is one of the main discovery mechanisms for Web services. UDDI, however, relies on the concept of a well-known central registry for description information. A more distributed concept for disseminating description information is the Web Services Inspection Language, also known as WS-Inspection (http://www-106.ibm.com/developerworks/webservices/library/ws-wsilspec.html).

Think of how business people exchange contact information. UDDI is the "phone book" model, where you can look up a business in a centralized registry and get complete information about how to access its services. WS-Inspection, on the other hand, is the "business card" model, where an entity such as a business or a node on a P2P network can provide a summary about itself, and pointers to where you can find more information about services it provides. In contrast to the UDDI model, information requests in the WS-Inspection model are made directly to the entity offering the service. WS-Inspection documents are very lightweight, and require very little maintenance because they are indirect references to information contained elsewhere, and they rely on existing standards such as WSDL and UDDI to convey actual descriptions.

An sample WS-Inspection document is shown here:

 <?xml version="1.0"?>  <inspection xmlns="http://schemas.xmlsoap.org/ws/2001/10/inspection/"             xmlns:wsiluddi=                 "http://schemas.xmlsoap.org/ws/2001/10/inspection/uddi/">   <service>     <abstract>A stock quote service with two descriptions</abstract>     <description referencedNamespace="http://schemas.xmlsoap.org/wsdl/"                  location="http://example.com/stockquote.wsdl"/>     <description referencedNamespace="urn:uddi-org:api">        <wsiluddi:serviceDescription location=            "http://www.example.com/uddi/inquiryapi">          <wsiluddi:serviceKey>4FA28580-5C39-11D5-9FCF-BB3200333F79              </wsiluddi:serviceKey>        </wsiluddi:serviceDescription>     </description>   </service>   <service>     <description referencedNamespace="http://schemas.xmlsoap.org/wsdl/"                  location="ftp://anotherexample.com/tools/calculator.wsdl"/>   </service>   <link referencedNamespace="http://schemas.xmlsoap.org/ws/2001/10/inspection/"         location="http://example.com/moreservices.wsil"/> </inspection>