Communications - June 2012

last line navigates and inlines the related Item entities within each Order. Other query constructs, such as $se-lect, $orderby, $top and $skip, are also supported as part of a request.

To provide interested readers with
a bit more detail, a graphical repre-
sentation of the external model (EDM)
together with examples of the OData
data service metadata and an AtomPub
response from an OData service can be
found in the sidebar “Service-Enabling
Data Sources.”
Driven by the mapping between
the EDM model and the underlying
data store’s relational model, the WCF
Data Services framework automati-
cally translates the above request into
the query language of the store. In our
example then, under the covers, the
above request would be translated into
the following SQL query involving a left
outer join:
products in this space.)

figure 3. integrating and service-enabling enterprise data.

SELECT Order.*, Item.*

FROM Customer JOIN Order LEFT OUTER JOIN Item
WHERE Customer.cid=’C43’
AND Order.status=’open’
The WCF Data Services framework
can also publish stored procedures as
part of an OData service, called Func-
tion Imports, which can be used for any
of the CRUD operations and are inte-
grated in the same URI-based query
interface.

integrated Data services

In the second data service usage scenario, data services are created to integrate as well as to service-enable a collection of data sources. The underlying sources are often heterogeneous in nature. The result of integration is that consumers of a data service see what appears to be one coherent, service-enabled data source rather than being faced with a hodgepodge of disparate schemas and data access APIs.

Figure 3 shows an example usage scenario. We will illustrate this use case using a commercial data services mid-dleware platform, the AquaLogic Data Services Platform, ALDSP, 13 developed at BEA Systems and later rebranded as ODSI, the Oracle Data Services Integrator. 38 ODSI is based on a functional model44 and the functional data service consuming method of Figure 1. (Again, we use ODSI as just one example of the