Conditions¶

Conditions are expressions evaluated against the TDM Information State. In Tala 31.0.1 they appear in if plan items and inside a goal's downdate_condition.

Definitions¶

<has_value predicate="p"/>
<has_shared_value predicate="p"/>
<has_private_value predicate="p"/>
<in_shared_commitments predicate="p" value="x"/>
<in_private_beliefs predicate="p" value="x"/>
<in_beliefs_or_commitments predicate="p" value="x"/>
<has_more_items predicate="p"/>
<has_more_items iterator="i"/>
<and>
  <has_value predicate="p"/>
  <not><in_private_beliefs predicate="p" value="x"/></not>
</and>

Conditions can be nested inside other conditions. They do not have standalone effects: they select an if branch or determine whether a goal may be downdated.

Condition forms¶

Form	True when
`has_value`	The predicate occurs in shared commitments or private beliefs.
`has_shared_value`	The predicate occurs in shared commitments.
`has_private_value`	The predicate occurs in private beliefs.
`in_shared_commitments`	The specified proposition is in shared commitments.
`in_private_beliefs`	The specified proposition is in private beliefs.
`in_beliefs_or_commitments`	The specified proposition is in either store.
`has_more_items`	A domain query enumeration or named iterator has more items.
`and`, `or`, `not`	Boolean combinations of nested condition expressions.

The XML attributes are:

Attribute	Applies to	Meaning
`predicate`	`has__value`; attribute form of `in_`; predicate-form `has_more_items`	Ontology predicate whose fact/value is checked.
`value`	Attribute form of `in_*`	Individual value. Omit it only for a nullary predicate.
`iterator`	Iterator-form `has_more_items`	Iterator whose remaining values are checked.

has_value, has_shared_value, and has_private_value require a predicate attribute. For in_*, predicate is used with the optional value attribute or a child proposition instead.

has_*_value tests whether a predicate has any stored value; it does not test for one particular value. For in_*, the proposition may be supplied by predicate/value attributes or as a child proposition. Child forms supported by the Tala 31.0.1 compiler include predicate propositions, perform, resolve, service_action_started, service_action_terminated, action_status, question_status, resolved, and know_answer.

Parents and children¶

Parent expressions: if and downdate_condition.
and and or contain one or more condition expressions; not contains exactly one. in_* conditions contain at most one proposition child.

Attribute and child forms¶

Attribute form for a predicate/value proposition:

<in_shared_commitments predicate="flight_status" value="late"/>

For a nullary predicate, omit value. For non-nullary predicates, provide a value of the ontology-declared sort.

Scope-specific value checks:

<has_value predicate="flight_status"/>
<has_shared_value predicate="flight_status"/>
<has_private_value predicate="flight_status"/>
<in_private_beliefs predicate="flight_status" value="late"/>
<in_beliefs_or_commitments predicate="flight_status" value="late"/>

has_value checks both shared commitments and private beliefs. The other has_*_value variants test their named store.

Child form for a service-action termination proposition:

<in_beliefs_or_commitments>
  <service_action_terminated name="BookRoom"/>
</in_beliefs_or_commitments>

Child form for a perform goal proposition:

<in_beliefs_or_commitments>
  <perform action="top"/>
</in_beliefs_or_commitments>

The service_action_terminated example checks only that the service call terminated, not whether it succeeded; see Invoke service action.

Boolean composition¶

and and or take one or more nested conditions. not takes exactly one.

<and>
  <has_value predicate="destination"/>
  <not>
    <in_private_beliefs predicate="destination" value="paris"/>
  </not>
</and>

DDD JSON¶

The JSON representation uses a single-key object per condition:

{
  "and": [
    {"has_value": {"predicate": "destination"}},
    {"not": {"in_private_beliefs": {"predicate": "destination", "value": "paris"}}}
  ]
}

The JSON schema and compiler also support or, in_* child propositions, has_more_items, and the other condition forms listed above.

has_more_items names either the predicate queried by a domain enumeration or the iterator:

<has_more_items predicate="possible_destination"/>
<has_more_items iterator="destination_iterator"/>

Tala reference and tests¶

XML condition grammar and child proposition forms: tala/ddd/schemas/domain.xsd
XML compilation: tala/ddd/ddd_xml_compiler.py
Truth evaluation: tala/model/condition.py
Tala tests: tala/ddd/test/test_ddd_xml_compiler.py and tala/model/test/test_condition.py