A free text description of the source of this data, e.g. a database or person name. This property should be used to describe the source of the data. This is meant to be used by databases that export their data to the BioPAX format or by systems that are integrating data from multiple sources. The granularity of use (specifying the data source in many or few instances) is up to the user. It is intended that this property report the last data source, not all data sources that the data has passed through from creation.
Source:http://www.biopax.org/release/biopax-level3.owl#dataSource