WCF Data Services (originally known as ADO.NET Data Services) is a framework for exposing data layers in a REST-ful manner, using JSON or Atom as the output format. WCF Data Services is a component of the .NET Framework that enables you to create services that use the Open Data Protocol (OData) to expose and consume data over the Web or intranet by using the semantics of REST (Representational State Transfer). OData exposes data as resources that are addressable by URIs. Data is accessed and changed by using standard HTTP verbs of GET, PUT, POST, and DELETE. OData uses the entity-relationship conventions of the Entity Data Model to expose resources as sets of entities that are related by associations.

While the technology is relatively new, it addresses a number of common use cases for developers, including:

• Allow AJAX applications access to the database via HTTP without writing a Web service as a proxy.
• Provide access to data to third-parties in a standardized, vendor neutral fashion.
• Create a REST-ful data access system without the baggage of other Web service systems.

The Open Data Protocol (OData) is an open web protocol for querying and updating data. The protocol allows for a consumer to query a datasource over the HTTP protocol and get the result back in formats like Atom, JSON or plain XML, including pagination, ordering or filtering of the data. OData is being used to expose and access information from a variety of sources, including but not limited to relational databases, file systems, content management systems, and traditional web sites. Microsoft has released OData under the Open Specification Promise (OSP) to allow anyone to freely interoperate with OData implementations. We intend on working with others in the community to move the features of OData into future version of AtomPub or other appropriate standards.

OData is defined as a set of open extensions/conventions to AtomPub documented and released under the OSP (Open Specification Promise).  

There is a growing list of products that implement the Open Data Protocol. Microsoft supports OData in SharePoint Server 2010, Excel 2010 (through SQL Server PowerPivot for Excel), Windows Azure Storage, SQL Server 2008 R2,Visual Studio 2008 SP1 and the .NET Framework. Microsoft provides client libraries for .NET, Silverlight, AJAX. Support in other Microsoft products is currently underway. Client libraries are also available for .NET, Silverlight, Windows Phone 7, PHP, AJAX, Javascript, Ruby, Objective C and Java.

Since the Open Data Protocol is fully specified, you can implement on any HTTP server using any language. On the .NET Framework, WCF.NET Data Services provides a framework allowing developers to create a OData services in .NET. Likewise in Java there is a server library called OData4J. As noted above, client libraries are available for .NET, Silverlight, Windows Phone 7, PHP, AJAX, Javascript, Ruby, Objective C and Java

There is a growing list of products that implement OData. Microsoft supports the Open Data Protocol in SharePoint Server 2010, Excel 2010 (through SQL Server PowerPivot for Excel), Windows Azure Storage, SQL Server 2008 R2, Visual Studio 2008 SP1. Support in other Microsoft products is currently underway.