I found the answer in WSAD 5.1.1's online help
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WDO data access
Dynamic Web applications can be used to access data sources; these applications are commonly refereed to as CRUD applications because they are able to Create, Read, Update, and Delete data. Though there are several data access frameworks to choose from, two are natively supported in the Web Perspective in WebSphere� Studio: Data Access Beans and WDO. WDO is a data-centric, disconnected, XML-integrated, data access mechanism that provides a source-independent result set. These features are very important aspects of a data access method optimized for Web applications, in particular dynamic Web applications that use Faces components.
Note: WDO is only supported if you are using WebSphere Application Server version 5.1 as your server.
Data-centric: Results are retrieved as a structured graph of data, rather than supporting the retrieval of objects (which include associated behaviors) as is the case with
EJB persistence mechanisms.
Disconnected: The retrieved result (graph of data) is independent of any associated connections or transactions.
XML-integrated: Services are provided to easily convert retrieved data to and from XML format.
Source-independent result set: The results of WDO queries are standardized because results returned from any type of data source are converted to a WDO graphical representation. For example, a WDO query against a
JDBC data source and a query against an EJB data source will both return a WDO structured result set that uses the same set of standard data types.
These WDO capabilities supplement the currently available object-oriented data access mechanism provided by EJB, and the data-centric, but connected mechanism provided by direct use of JDBC.
WDO and Faces components work together to provide an easy way to create a dynamic Web application that accesses data using a method optimized for the Web. There are two data access beans that are made available as Faces components in the Palette view:
Relational Data Object (DataObjectAccessBean)
Relational Data List (DataListAccessBean)
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