ambiguous semantics of duty constraints #211

reopening as #112 (comment) and issues outlined in #191 are still not addressed..

Issue

http://w3c.github.io/poe/model/#rule:

For a Rule to become effective, it MUST be valid (i.e., all it's Constraints MUST be satisfied).

http://w3c.github.io/poe/model/#constraint:

For a Rule, if the Constraint is satisfied then the action becomes effective for the enclosing Rule.
[..] A Rule becomes effective if all of its Constraints are satisfied.

http://w3c.github.io/poe/model/#constraint-class:

If the expression evaluates to true the Constraint is satisfied.

effective (ɪˈfɛk tɪv) adj.

1. adequate to accomplish a purpose; producing the intended or expected result: effective teaching methods.
2. in operation or in force; functioning; operative: The law becomes effective at midnight.
3. producing a deep or vivid impression; striking: an effective photograph.
4. prepared and available for service, esp. military service.

Interpretation

1. A Rule becomes effective if all of its Constraints are satisfied
2. Duty is a type of Rule
3. in effect means in force/active 
4. A Constraint is satisfied if it evaluates to true
--------------
=> A Duty is only in force/active if all of its Constraints evaluate to true.

Problematic Examples

<http://example.com/policy:42>
    a odrl:Agreement ;
    odrl:obligation [ 
	# a odrl:Duty ;
        odrl:assignee <http://example.com/person:44> ;
        odrl:assigner <http://example.com/org:43> ;
        odrl:action odrl:compensate ;
        odrl:constraint [ 
            odrl:leftOperand odrl:payAmount ;
            odrl:operator odrl:eq ;
            odrl:rightOperand "500.00" ;
            odrl:unit <http://dbpedia.org/resource/Euro> ;   
        ]
    ] .

should => "person44 has the obligation to pay 500 euro to org43"
is => "As long as payAmount != 500 euro, the duty is not in effect hence no one has to pay anything"

<http://example.com/policy:42>
    a odrl:Agreement ;
    odrl:obligation [ 
	# a odrl:Duty ;
        odrl:assignee <http://example.com/person:44> ;
        odrl:assigner <http://example.com/org:43> ;
        odrl:action odrl:compensate ;
        odrl:constraint [ 
            odrl:leftOperand odrl:payAmount ;
            odrl:operator odrl:eq ;
            odrl:rightOperand "500.00" ;
            odrl:unit <http://dbpedia.org/resource/Euro> ;   
        ] ;
        odrl:constraint [ 
            odrl:leftOperand odrl:dateTime;
            odrl:operator odrl:gt ;
            odrl:rightOperand "2017-12-31" ;
        ]
    ] .

should => "Starting from 2018-01-01 onwards, person44 has the obligation to compensate org43. This duty is only considered to be fulfilled, if payed amount equals 500 euro"
is => "As long as payAmount != 500 euro or datetime <= 2017-12-31, the obligation to compensate org43 is not in effect"

Proposal

Distinguish between different interpretations of duty constraints:

:duty odrl:constraint :c1 -> :duty is in effect iff :c1 is satisfied
:duty odrl:scope :c2 (or any other name for scope) -> :duty is fulfilled iff :c2 is satisfied

<http://example.com/policy:42>
    a odrl:Agreement ;
    odrl:obligation [ 
	# a odrl:Duty ;
        odrl:assignee <http://example.com/person:44> ;
        odrl:assigner <http://example.com/org:43> ;
        odrl:action odrl:compensate ;
        odrl:scope [ 
            odrl:leftOperand odrl:payAmount ;
            odrl:operator odrl:eq ;
            odrl:rightOperand "500.00" ;
            odrl:unit <http://dbpedia.org/resource/Euro> ;   
        ] ;
        odrl:constraint [ 
            odrl:leftOperand odrl:dateTime;
            odrl:operator odrl:gt ;
            odrl:rightOperand "2017-12-31" ;
        ]
    ] .

should => "Starting from 2018-01-01 onwards, person44 has the obligation to compensate org43. This duty is only considered to be fulfilled, if payed amount equals 500 euro"
is => "Starting from 2018-01-01 onwards, person44 has the obligation to compensate org43. This duty is only considered to be fulfilled, if payed amount equals 500 euro"