Roleset tap.01 Verbnet Class: 1 "hit":

Roles:

Arg0:agent, hitter - animate only!


Arg1:thing hit


Arg2:instrument, thing hit by or with

Examples:

duck duck goose (-)
Mary tapped John on the head with a 2x4.
Arg0:	Mary
REL:	tapped
Arg1:	John
Argm-LOC:	on the head
Arg2-with:	a 2x4

Poor John.

Roleset tap.02 Verbnet Class: NONE "call upon":

Roles:

Arg0:caller


Arg1:thing being summoned


Arg2:benefactive


Arg3:attribute of arg1 or task

Examples:

just transitive (-)
RJR Taps FCB/Leber
Arg0:	RJR
REL:	Taps
Arg1:	FCB/Leber




with task (-)
The investor was instrumental in *trace* tapping Mr. Wolf to run the air cargo unit of Tiger International Inc.
Arg0:	*trace* -> The investor
REL:	tapping
Arg1:	Mr. Wolf
Arg3:	to run the air cargo unit of Tiger International Inc

The automatic tagger fails to separate Args 1,3.

Roleset tap.03 Verbnet Class: NONE "access, as a phone or water tap":

Roles:

Arg0:accessor, agent


Arg1:thing tapped

Examples:

transitive, active (-)
The charity admits spending a lot on fund raising, but says that was necessary to establish a donor base *trace* it can tap *trace* at much lower cost in years to come.
Arg0:	it
ArgM-MOD:	can
REL:	tap
Arg1:	*trace* -> *trace* -> a donor base
ArgM-MNR:	at much lower cost
ArgM-TMP:	in years to come

The call upon sense might be a metaphorical extension of this sense.