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Language Specification - Transfer Definition (TDF) - Semantics

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Transfer-action

The transfer action defines the direction of the communication. The ‘send’ action states that belief(s) of the initiating agent or object matching the transfer definition are transferred from the initiating agent or object to the non-initiating agent or object. The ‘receive’ action states that belief(s) of the non-initiating agent or object matching the transfer definition are transferred from the non-initiating agent or object to the initiating agent or object. Note that if the transfer definition specifies a condition as an object/attribute tuple (OA=V) the right hand side value is ignored in the matching process. To make this behavior clearer, the condition may be stated without the equality and right hand side (OA) or the right hand side may be given as a wildcard character (OA=?). In the case of an ORO, the right hand side is not ignored in the matching process but it may be omitted from the condition (OR) or given as the wildcard character (OR?) to indicate that any right hand side object should match the condition.

< Class Variable >

To provide more flexibility in determining the beliefs to be transferred in a communication a transfer definition condition may use bracketed class variables. A transfer definition condition, instead of specifying the name of a variable, parameter or concept instance (agent, object, conceptual object, or area), may specify the class of concept in between the brackets < and > such as <BaseGroup>. A class variable may be used anywhere a concept reference may appear in the condition. It may be used either on the left-hand or right-hand sides of the condition and may appear as a standalone object reference or paired with an attribute name. This will have the transfer condition match all beliefs that have a concept instance in a position corresponding to the class variable that is an instance of the specified class or an instance of any of its subclasses. The matches can be restricted by specifying a more specific class in the transfer definition condition. The agent or object will in that case only send beliefs involving those instances that are instances of that class or any of its subclasses, but not any of its superclasses, even if the superclass defines the attribute or relation and beliefs for concept instances of that super class exist.

Wildcard

A wildcard character, ‘?’, may be used on the right-hand side of a transfer definition condition to indicate that the right-hand side value or object of a matching belief is ignored. Normally, this may be stated more directly by simply omitting the operator and right-hand side of a value comparison or by omitting the right-hand side object of a relation comparison. However, the wildcard may occasionally be useful in a relation comparison together with ‘is false’ or ‘is unknown’ to transfer beliefs with truth values other than ‘true’.
 

Constraints

1. In the comparison the left hand side attribute type and the right hand side value-type or right hand side attribute type of a value-expression must be the same. Object-attribute-index is considered type compatible with any type and is permitted on both the left and right hand side. Since the right hand side of the condition is ignored, no errors or warnings will ever be generated event if the value resulting from the right hand side is type incompatible.

2. In the comparison the left hand side and right hand side types in a relational expression must match the types as defined for the relation used in the relational expression.

3. An ID.name when used in a class variable must be the name of a concept class, i.e. a group, class, conceptual class or area definition.

4. If a communicative-act is specified and the action is send then the object-name or value passed to the parameter identified by param-name must be an object instance that is an instance of brahms.communication.CommunicativeAct.

5. If a communicative-act is specified and the action is receive then the object-name or value passed to the parameter identified by param-name must be an object instance that is an instance of brahms.communication.CommunicativeAct and the value for the communication activities ‘with’ property must be identical to the communicative-act specified in the transfer definition to indicate the reading of the communicative-act’s beliefs.