The BPMN2 validation rules included in the BPMN2 Completeness validation rules suite are described in the table.

Validation rule 

Severity

An Intermediate Boundary Event should have an outgoing Sequence Flow.

Info

An Intermediate Event should have an incoming or outgoing Sequence Flow. Info
An Error Code should be specified for an Error End Event. Info
An Event-Based Gateway should have two or more outgoing Sequence Flows. Info
An Event SubProcess will have one Start Event.

Warning

A Start Event shall have at least one outgoing Sequence Flow. Warning
An Intermediate Event can have either an incoming or outgoing Message Flow. It cannot contain both.Warning