Given the following relationship graph
Without inspecting the data, what is known about this solution? 

The Event table occurrence references a table from an external ODBC Data Source. 

There can be zero or one, but no more than one, Event record related to any Task record. 

The corner arrows indicate all three table occurrences reference tables from external data sources. 

From a layout based on the Event table occurrence, a portal could be drawn showing both related Task and Volunteer data.