Downdate conditions¶

A downdate_condition is a child of a goal. When the goal's condition becomes true, TDM treats the goal as fulfilled and downdates it. Multiple conditions on one goal are alternatives: any one true condition is sufficient.

Syntax¶

<goal type="perform" action="book_room">
  <plan>
    <invoke_service_action name="BookRoom"/>
  </plan>
  <downdate_condition>
    <in_beliefs_or_commitments>
      <service_action_terminated name="BookRoom"/>
    </in_beliefs_or_commitments>
  </downdate_condition>
</goal>

The child of downdate_condition is a normal condition expression. It can be a predicate/value condition, an in_* proposition condition, a value test, or a Boolean composition. Each condition is evaluated against the active TIS.

Service actions: termination is not success¶

TDM records service_action_terminated whenever an invoked service action returns, including when its result is unsuccessful. With postconfirm, the termination proposition is stored in private beliefs; without it, it is stored in shared commitments. in_beliefs_or_commitments checks both locations. Therefore, this condition means “the service call ended,” not “the operation succeeded.”

The old invoke_service_action/@downdate_plan attribute does not create an implicit downdate condition in Tala/TDM 31.0.1. It is retained by the XML/JSON models for compatibility; author an explicit condition for current behavior.

Downdate and cleanup behavior¶

TDM also downdates a perform/resolve goal when the corresponding action or question status is committed. For explicit conditions, TDM evaluates each condition and clears the propositions named by in_* conditions from the corresponding TIS store when the goal is downdated. Boolean and/or conditions clean their satisfied branches. has_value checks predicate presence without identifying a specific proposition to remove, and not does not remove facts.

The XML schema retains <postcond> as a compatibility form. New DDDs should use <downdate_condition>.

Tala sources and examples¶

Schema/compiler: tala/ddd/schemas/domain.xsd, tala/ddd/ddd_xml_compiler.py
Goal-to-condition mapping: tala/model/domain.py
Tala tests: tala/ddd/test/test_ddd_xml_compiler.py and tala/model/test/test_domain.py