Semantics of Permission, Prohibition, and Obligation
The deontic modalities of Permissions, Prohibitions and Obligations can be represented in ODRL as instances of the classesodrl:Permission, odrl:Prohibition and odrl:Duty.Instances of the class
odrl:Duty may have the following different meanings in ODRL:
- An instance of the class
odrl:Dutyrepresents an Obligation when it is connected to theodrl:Policythrough theodrl:obligationproperty. An Obligation can be activated, violated, or fullfilled. - An instance of the class
odrl:Dutyrepresents a Condition for a Permission to be active when it is connected to the odrl:Permission through the odrl:duty property. When an instance of theodrl:Dutyclass is used as an activation condition of a Permission, it can be active, fulfilled or not fullfilled. This is a crucial difference between a Duty that represents an activation condition of a Permission and a Duty that represents an Obligation. - An instance of the class
odrl:Dutyrepresents a consequence (sanction) when it is connected to theodrl:Dutythrough theodrl:consequenceproperty. - An instance of the class
odrl:Dutyrepresents a remedy for a odrl:Prohibition when it is connected to theodrl:Dutythrough theodrl:remedyproperty.
Here follows a list of properties (with their possible values) needed by the ODRL Evaluator:
- Permission, Prohibition, Obligation (duty at the root level), Condition (duty not at the root level) have a property called activation state, which can take the values of active or inactive.
- Prohibition, Obligation, and Condition have a property called deontic state, which can take the values of not-set, or violated, or fulfilled. They can become violated or fulfilled only when they are active.
- Permission have a property called usage state, which can take the value of used or not-used. A permission can become used only when it is active.
- Constraint (connected to the Rule using the odrl:constraint property) has a property called satisfaction state which can take the values of satisfied or not-satisfied. A not-satisfied constraint may become satisfied and return to being not-satisfied. The value of the satisfaction state of a Constraint is calculated according to the state of the world. Constraints directly defined at policy level are not directly considered.
- Refinement (connected to an Action, to an AssetCollection, or to a PartyCollection using the
odrl:refinement property) has a property called satisfaction state
which can take the values of satisfied or not-satisfied.
- In the access control scenario, the value of the satisfaction state of a Refinement is computed according to the action that an agent attempts to perform on digital resources.
- In the monitoring scenario, the value of the satisfaction state of a Refinement is computed according to the actual actions that are performed by agents and that are represented in the state of the world.
- Action (connected to the Rule with the odrl:action property) has a property called performance state
which initially takes the values not-performed and
can become performed when an action with all the properties values (i.e.
type,performer,object,...) that matches with the values described in the Rule (i.e.action,assignee,target) is actually performed at a given instant of time and its performance is represented in the state of the world.
The mechanisms for computing the activation of Permissions, Prohibitions, and Obligations and the violation or fulfillment of Prohibitions and Obligations are all different. Therefore we continue by discussing the semantics of Permissions, Prohibitions, and Obligations in separated sections.
Sematics of Permission
In ODRL 2.2., a Rule that belongs to the odrl:Permission class is active (the action is permitted) if:- all the existing constraints of the Rule are satisfied;
- all the existing duties of the Rule are fulfilled or inactive;
- (only for the access control scenario) all the existing refinements of the Action, AssetCollection, PartyCollection are satisfied by the attempted action.
When an action (with all the refinements satisfied) regulated by an active permission is performed the permission is used.
In the access control scenario: if one of the refinements of the attempted action does not satisfy the refinements of the permission, and there is not another active permission that permits such an action, it means that the action is not permitted and it is blocked.
In the monitoring scenario: When an action A is performed, if there is no active permission to do so (i.e. there is no active permission regulating a class of action to which the executed action belongs) and the default setting for the ODRL Evaluator is set to "everything is prohibited unless explicitly permitted" a violation is generated. This evaluation is not exemplified below.
Examples (Permission without duties)
The ODRL policy examples used below to exemplify the semantics of Permission are partially taken from the examples in the ODRL Information Model.Example 13
Type of Permission: Permission only constrained by Constraint(s).
The permission below allows the target asset
http://example.com/document:1234 to be distributed,
it includes a constraint C that the permission can only be exercised until 2018-01-01.
{
"@context": "http://www.w3.org/ns/odrl.jsonld",
"@type": "Set",
"uid": "http://example.com/policy:6163",
"profile": "http://example.com/odrl:profile:10",
"permission": [{
"target": "http://example.com/document:1234",
"assigner": "http://example.com/org:616",
"action": "distribute",
"constraint": [{
"leftOperand": "dateTime",
"operator": "lt",
"rightOperand": { "@value": "2018-01-01", "@type": "xsd:date" }
}]
}]
}
Time evolution of Permission P6163
The constraint C must be evaluated on the state of the world, which must include a representation of the current time (for example by using the Time Ontology in OWL). As long as the current time (represented in the state of the world) is before the first day of 2018, the permission P6163 is active. When the first day of 2018 is passed, the authorisation becomes inactive. (The activation of this type of permission does not depend on the actions attempted by the agents).
| ID | P6163.Const | P6163 |
|---|---|---|
| E13-1 | satisfied | active |
| E13-2 | not-satisfied | inactive |
type is distribute
and its object is equale to http://example.com/document:1234
and the permission P6163 is active then the action is performed, otherwise it is blocked.Monitoring scenario. If an action with
type equal to distribute
and object is equale to http://example.com/document:1234 is
performed (it is represented in the state of the world as performed)
when the permission is active, then the permission is used.Example 14
Type of Permission: Permission that regulates an action that is refined by Refinement(s).
The permission below allows the target asset
http://example.com/document:1234to be printed and also include a refinement indicating that the resolution
of the printing action must be less than or equal to 1200 dpi.
{
"@context": "http://www.w3.org/ns/odrl.jsonld",
"@type": "Set",
"uid": "http://example.com/policy:6161",
"profile": "http://example.com/odrl:profile:10",
"permission": [{
"target": "http://example.com/document:1234",
"assigner": "http://example.com/org:616",
"action": [{
"rdf:value": { "@id": "odrl:print" },
"refinement": [{
"leftOperand": "resolution",
"operator": "lteq",
"rightOperand": { "@value": "1200", "@type": "xsd:integer" },
"unit": "http://dbpedia.org/resource/Dots_per_inch"
}]
}]
}]
}
The time evolution of Permission P6161 above depends on the scenario.
Acces control scenario: Given a formal description of the attempted action, if its
type is print,
its object is equale to http://example.com/document:1234,
and its resolution is less than or equal to 1200 dpi (it satisfies the refinement) then the permission P6161
is active and the attempted action is performed, otherwise the permission P6161 is inactive and the action is blocked.| ID | P6161.action.Ref | P6161 | Attempted Action | P6161.usage state |
|---|---|---|---|---|
| E14-1-ac | not-satisfied by the attempted action | inactive | not-performed | not-used by the attempted action |
| E14-2-ac | satisfied by the attempted action | active | performed | used by the attempted action |
Monitoring scenario: The above Permission is always active because it has neither constraints nor duties. Given a formal description a performed action, if its
type is print,
its object is equale to http://example.com/document:1234, and its
resolution is less than or equal to 1200 dpi (it satisfies the refinement)
then the permission is used otherwise it is not used. In this scenario, the permission is active even if the refinement is not satisfied, because the activation state of the permission
is computed independently from the refinement of the regulated action.| ID | P6161 | P6161.action.Ref | P6161.usage state |
|---|---|---|---|
| E14-1-m | active | satisfied by the performed action | used by the performed action |
| E14-2-m | active | not-satisfied by the performed action | not-used by the performed action |
Semantics of Duty when it is used as an activation Condition of a Permission
Goal: determine if a Duty is fulfilled.In ODRL 2.2., a Rule that belongs to the Duty class is fulfilled if all its constraints are satisfied and if its action, with all refinements satisfied, has been performed.
The initial state of a duty is inactive.
In order to evaluate if a Duty is fulfilled, it is necessary to perform the following steps:
- Evaluate the satisfaction of its Constraints (output: satisfied, not satisfied) on the state of the world;
- if its Constraints are all satisfied the duty is active.
- if one of its Constraints is not satisfied the duty is inactive. (For example, the duty to pay a ticket to get an active permission enter a museum may be active only on Sundays). - If the Duty is active and its action with all refinements satisfied, is performed the duty becomes fulfilled.
Examples (Permission with duties)
Example 22Type of Permission: Permission that is constrained by a Duty. The Duty has not Constraints. The Duty regulates an Action that is refined by Refinement(s).
The Permission below is granted by the Party
http://example.com/assigner:sony. It allows the
target asset http://example.com/music/1999.mp3 to be played.
The permission includes a duty to perform the compensate action that has a refinement of payAmount
of euro 5.00.
The semantics of Permission requires that the compensate action (included in the duty) must be performed
before the play action in order to get an active permission to perform the play action.
{
"@context": "http://www.w3.org/ns/odrl.jsonld",
"@type": "Set",
"uid": "http://example.com/policy:88",
"profile": "http://example.com/odrl:profile:09",
"permission": [{
"assigner": "http://example.com/assigner:sony",
"target": "http://example.com/music/1999.mp3",
"action": "play",
"duty": [{
"action": [{
"rdf:value": { "@id": "odrl:compensate" },
"refinement": [{
"leftOperand": "payAmount",
"operator": "eq",
"rightOperand": { "@value": "5.00", "@type": "xsd:decimal" },
"unit": "http://dbpedia.org/resource/Euro"
}]
}]
}]
}]
}
The Permission P88 is active if its Duty is fulfilled, otherwise it is inactive.
The Duty has not Constraints, so it never inactive, it starts to be active and can become fulfilled when in the state of the world
there is a representation that a payment action
of 5 euro to the assigner of the permission is performed.| ID | Duty.Action.Ref | Duty |
|---|---|---|
| E22 | not satisfied by performed actions | active |
| E22 | satisfied by the correct payment action | fulfilled |
Acces control scenario: Given a formal description of the attempted action, if its
type is play
and its object is equale to http://example.com/music/1999.mp3
and the Permission P88 is active then the action is performed, otherwise it is blocked.| ID | Duty | P88 | Attempted Action | P88.usage state |
|---|---|---|---|---|
| E22-1-ac | active | inactive | not-performed | not-used by the attempted action |
| E22-2-ac | fulfilled | active | performed | used by the attempted action |
Monitoring scenario: Given a formal description a performed action, if its
type is play
and its object is equale to http://example.com/music/1999.mp3
and the Permission P88 is active then the Permission is used, if the Permission P88 is inactive the permission is not used
(there might be a violation but it depends on the other permissions and the default assumption
as to what is prohibited).
| ID | Duty | P88 | P88.Action | P88.usage state |
|---|---|---|---|---|
| E22-1-m | active | inactive | performed | not-used |
| E22-2-m | fulfilled | active | performed | used |
Sematics of Prohibition
In ODRL 2.2., a Rule that belongs to the odrl:Prohibition class is active (its action, with all refinements satisfied cannot be exercised) if all constraints of the Rule are satisfied, otherwise it is inactive.In order to evaluate if a prohibition is active, it is necessary to evaluate the satisfaction of its constraints on the state of the world (constraints are either satisfied or unsatisfied).
Duties on prohibitions have no defined meaning.
An ODRL Evaluator will determine that a violation has been produced if the action on an active prohibition is executed. If multiple actions are related to a single prohibition, the execution of a single action will result in a violation. The ODRL Evaluator will calculate the state of an active prohibition to be within one of these possibilities:
- not violated when the regulated action with all refinements satisfied has not been executed;
- violated when the regulated action with all refinements satisfied has been executed;
odrl:consequence for its violation. Sematics of Obligation
In ODRL 2.2., an Obligation that belongs to theodrl:Duty class (it would be better to have an odrl:Obligation class) is active (its action,
with all refinements satisfied, should be perfomed) if all constraints of the Rule are satisfied, otherwise it is inactive.An active Obligation becomes:
- fulfilled or not violated when the regulated action with all refinements satisfied is executed;
- violated when the regulated action with all refinements satisfied can no longer be executed;
- unknown when the regulated action with all refinements satisfied can be executed but has not been so far;
odrl:consequence of not fulfilling that obligation. Problem: reasoning about deadline.