The FactoryTalk View documentation uses the term data source as a generic term that includes all possible sources of tag data, for both data server tags and HMI tags.
The data source can be memory or a device such as a programmable logic controller or OPC server. The application writes values to and reads values from the data source.
The data source is configured to exchange information (in the form of numeric or string values) between the application and the physical machine that your project is controlling.