required fields too restrictive on equipment

[smrgeoinfo]

in equipment, not null constraints are too restrictive
equipmentmodelid integer NOT NULL,
equipmentserialnumber varchar (50) NOT NULL,
equipmentownerid integer NOT NULL,
equipmentvendorid integer NOT NULL,
equipmentpurchasedate timestamp NOT NULL,
This information is rarely known for legacy data.
Not only that, but modelid, owerid, and vendorid are foreign keys to equipment models, people and organizations, so in cases where the information is not known, a dummy record has to be present as the target of the FK. These fields should all be nilable, with recommended nil-values like OGC uses (missing, not applicable, with held...).