Building DADX Files
At the heart of WORF are the DADX files, which specify how to create a Web service using SQL operations. DADX supports all SQL operations, including queries, updates, and calls to stored procedures.

A DADX file is an XML document. The root node is a DADX node, but the real work is done within the operation nodes. Listing 1 shows a very simple DADX file defining a Web service called getWorkForEmployee, which receives an employee ID and returns a collection of two-tuples, each containing the call number and the action number.

DADX also supports update operations. As an example, Listing 2 shows the DADX file used for the second Web service on our list - a Web service that updates the status of a call. The operation in this DADX file is an update operation that wraps an SQL update statement. Note that in addition to the operation, a documentation element has been added; this will find its way into the WSDL file that's automatically generated by WORF on your behalf. Finally, Listing 3 shows the DADX document for the third Web service wrapping a call to a stored procedure. Incidentally, a DADX file may contain many operation elements, each transformed into a Web service by WORF.

Deploying and Calling WORF Web Services
You need to do a bit of setup before you can start accessing your DADX-based Web services. Specifically, you need to set up a WORF group and specify the database properties that will be used to access the database. After all, the DADX files define the SQL commands but don't specify the database instance to which the SQL should be applied.

Database properties are specified within a groups.properties file, as shown in Listing 4. This file tells WAS which JDBC driver to load and how to connect to the database. It also defines reload parameters allowing you to modify the DADX files and have WAS reload the definitions automatically. In our example, the groups.properties should be placed in a folder called callWS under {WAS_HOME}/App Server/installedApps/servicesApp.ear/WEB-INF/classes/groups. Your DADX files should also be placed here.

You need to inform the WORF that you've created a new group and the associated Web services. For each group, add a DxxInvoker servlet to your web.xml file within the Web application. Each invoker servlet handles a set of Web services that access the same DB2 instance. Listing 5 shows the additions to the web.xml file required to support the CALL Web services; now you're ready to start using the Web services.

WORF supports both HTTP bindings and a SOAP binding. When invoking a WORF Web service using an HTTP GET binding, use a URL of the form http:// <host>/callWS/getWorkForEmployee.dadx/getWorkForEmployee?employee_id=112001. This invokes the first operation shown in Listing 1, passing in the employee ID to be used by the SQL query. The same form of invocation would be used in an HTTP POST request, except that the parameter would be passed within the request body.

To use the SOAP binding, activate a URL of the form http://<host>/ call WS/getWorkForEmployee.dadx/SOAP. The input arguments are passed in as a SOAP request within the body of the request. If all operations are packaged together in a single DADX file (let's assume all operations are inside the CALL.dadx file), the invocation over HTTP GET would take the form of http://<host>/callWS/ CALL.dadx/ getWorkForEmployee?employee_id=112001. Invocation over SOAP would always use a URL of the form http://<host>/callWS/ CALL.dadx/ SOAP, while the SOAP request would embody the actual operation that needs to be invoked.

WSDL and Schema Files
WORF is used not only at runtime for wrapping the SQL operation as a Web service in the context of an invocation; it also generates all that's required to deploy your Web service. WORF can automatically generate a Web Services Description Language (WSDL) file, which allows others to learn how to use your Web service. You can publish this WSDL document in a UDDI registry.

For example, to get the WSDL file for the query shown in Listing 1, simply access a URL of the form http:// <host>/callWS/getWorkForEmployee.dadx/WSDL. This will return a WSDL document that describes your Web service. If you want to publish your Web service on a UDDI registry, you actually need the WSDL delivered in two files - a service file and a binding file. To retrieve these documents use the following two URLs:

http://<host>/callWS/getWorkForEmployee.dadx/WSDLservice
http://<host>/callWS/getWorkForEmployee.dadx/WSDLbinding

WORF even takes care of generating schema files for you. Regardless of whether you use advanced XML manipulation with the XML Extender (in which case metadata is often held as DTDs), you can easily retrieve XSD files for your Web service. As an example, to generate an XSD file for the getWorkForEmployee Web service simply access a URL of the form http://<host>/callWS/getWorkForEmployee.dadx/XSD.

Advanced XML Manipulation
WORF supports two types of Web services: SQL-based operations and XML-based operations. The DADX documents shown above have all been SQL-based operations. XML-based operations allow you to compose XML documents from relational data and store it. You can create as complex a mapping as is required to allow you to make the most of your relational store without compromising your XML layouts. This uses advanced XML collection operations supported by the DB2 XML Extender, a package that allows you to store and retrieve XML documents from DB2 using flexible metadata definitions. To use these advanced features you must have the DB2 XML Extender option installed, and you need a more thorough understanding of how to use DAD files. This requires a bit of learning; for more details, see the Resources section.

Summary
WORF allows you to Web service-enable your DB2 database and leverage your investment in the database schema and its procedures by autowrapping them with Web services deployed on WAS. You can do this easily by writing a simple DADX file and inserting it into an appropriate groups directory.

Because so many of today's systems are database-centric, many of the Web services you may need to build involve either database operations or storing/retrieving data from your data store. I hope that when you have such a task you remember WORF and the work it can save you. While this two-part series introduced you to the subject, it is by no means a complete overview of WORF, XML Extender, DADX, or DAD files. The resources below provide all you need to build and deploy DB2-based Web services.

Resources