Constraints on Constraints (aka Complex Constraints)

The purpose of this page is to collect proposals for addressing use cases that require means for defining more expressive/complex constraints on permissions, prohibitions or duties. For example, one may wants to define:

• relative constraints, such as "You can publish photos to do with a football match, but only 1 hour after the event (i.e., respective football match) has ended."
• or qualified constraints (scope of constraints?) to distinguish between "payment per account" and "payment per person".

Both of which are currently not (or only partially?) ...

According to our current Information Model ED, constraints in ODRL are defined as follows:

ODRL Constraints - current status (as of 10/11/2016)

The Constraint entity indicates limits and restrictions to the Permission, the Prohibition and the Duty entity. Constraints express mathematical terms with two operands and one operator. For example, the "number of usages" (name) must be "smaller than" (operator) the "number 10" (rightOperand). If multiple Constraint entities are linked to the same Permission, Prohibition, or Duty entity, then all of the Constraint entities MUST be satisfied. That is, all the Constraint entities are (boolean) ANDed. In the case where the same Constraint is repeated, then these MUST be represented as a single Constraint entity using an appropriate operator value (for example, isAnyOf). The Constraint entity contains the following attributes: name: a name that identifies the left operand of the operation (REQUIRED) identifies the left operand of the mathematical operation for the Constraint such as "Number of Usages" and "Expiration Date" etc. operator: an operator function (REQUIRED) identifies the comparative operation such as "greater than" or "equal to" rightOperand: the right operand of the operation (REQUIRED) identifies the value that is being compared dataType: the datatype of the rightOperand (OPTIONAL) indicates the type of the rightOperand, such as "decimal" or "datetime" unit: the units of the rightOperand (OPTIONAL) indicates the unit value of the rightOperand, such as "EU dollars" status: the current value of the left operand (OPTIONAL) provides the current value of the Constraint variable (i.e. current value of name) When processing policy expressions, these Constraint names MAY be directly linked to a procedure that can determine the outcome of the operations, such as the number of already performed usages and the current date. The name and operator are defined in the ODRL Vocabulary or community profiles.