As the manual states:
“Use PI Coresight to search for PI data from all of your PI Systems, PI AF databases, or to search for previously saved displays created with PI Coresight. Search results are returned in a single results list.”
PI Coresight can access data directly only from the PI System (PI Server and AF Server). However, AF Server lets you set up a lot of different data sources from AF attributes through the data reference and ConfigString. For instance, if you want to create an attribute linking it to a PI Point, you should choose the PI Point Data Reference. If you want to create an attribute linking it to a table stored on a SQL Server database you should choose Table LookUp Data Reference.
You are able to develop your custom data reference and register it on AF. Please refer to this white paper for more information.
Hope this helps!