WSO2 Data Services feature provides a convenient Web service interface for data stored in sources such as relational databases, CSV files and MS-Excel files. With WSO2 Data Services, data can be exposed and accessed in a secure (using WS-Security) and reliable (using WS-ReliableMessaging) manner; data is also made available for mashing-up with other Web services.
WSO2 Data Services is shipped as a separate product as well. You can download it from here. It is also added into WSO2 Application Server as it is more easy to manage all kinds of Web Services (Axis2, JAX-WS, Data Services etc) in a single server. And also it's a common use case in production systems to run Axis2 services together with Data services.
In WSO2 Carbon platform, there are Data Services related features which can be installed into any of our Carbon based product. Therefore, in both WSO2 AS and WSO2 DSS, same set of Data Services features are used. So you can select the best option depending on your requirement.
If you are interested in running Data Services related samples, please download the WSO2 Data Services Server binary distribution from here. We will be including those samples in AppServer also in future releases.
You can find more useful articles and tutorials on Data Services from here as well.