Q: (owns ?p ?c) (type ?c Car) (has-color ?c Red)
   must-bind ?p don't-bind ?c
A: (exists ?c (and (owns Joe ?c) (type ?c Car) (has-color ?c Red)))

<dql:query xmlns:dql="http://www.daml.org/2002/10/dql-syntax#"
           xmlns:var="http://www.daml.org/2002/10/dql-variables#">
  <dql:queryPattern>
    <rdf:RDF>
      <rdf:Description rdf:about="http://www.daml.org/2002/10/dql-variables#p">
        <owns rdf:resource="http://www.daml.org/2002/10/dql-variables#c"/>
      </rdf:Description>
      <Car rdf:ID="http://www.daml.org/2002/10/dql-variables#c">
        <has-color rdf:resource="#Red"/>
      </Car>
    </rdf:RDF>
  </dql:queryPattern>
  <dql:mustBindVars>
    <var:p/>
  </dql:mustBindVars>
  <dql:answerKBPattern>
    <dql:kbRef rdf:resource="http://joedata/joe.daml"/>
  </dql:answerKBPattern>
  <dql:answerSizeBound>5</dql:answerSizeBound>
</dql:query>

<dql:answerBundle xmlns:dql="http://www.daml.org/2002/10/dql-syntax#"
                  xmlns:var="http://www.daml.org/2002/10/dql-variables#">
  <dql:queryPattern>
    <rdf:RDF>
      <rdf:Description rdf:about="http://www.daml.org/2002/10/dql-variables#p">
        <owns rdf:resource="http://www.daml.org/2002/10/dql-variables#c"/>
      </rdf:Description>
      <Car rdf:ID="http://www.daml.org/2002/10/dql-variables#c">
        <has-color rdf:resource="#Red"/>
      </Car>
    </rdf:RDF>
  </dql:queryPattern>
  <dql:answer>
    <dql:binding-set>
      <var:p rdf:resource="#Joe"/>
    </dql:binding-set>
    <dql:answerPatternInstance>
      <rdf:RDF>
        <rdf:Description rdf:about="#Joe">
          <owns rdf:resource="http://www.daml.org/2002/10/dql-variables#c"/>
        </rdf:Description>
        <Car rdf:ID="http://www.daml.org/2002/10/dql-variables#c">
          <has-color rdf:resource="#Red"/>
        </Car>        
      </rdf:RDF>
  </dql:answer>
  <dql:continuation>
    <dql:none/>
  </dql:continuation>
</dql:answerBundle>


Q: (has-father Bill ?f)
   must-bind ?f
A: No answers


<dql:query xmlns:dql="http://www.daml.org/2002/10/dql-syntax#"
           xmlns:var="http://www.daml.org/2002/10/dql-variables#">
  <dql:queryPattern>
    <rdf:RDF>
      <rdf:Description rdf:about="#Bill">
        <has-father rdf:resource="http://www.daml.org/2002/10/dql-variables#f"/>
      </rdf:Description>
    </rdf:RDF>
  </dql:queryPattern>
  <dql:mustBindVars>
    <var:f/>
  </dql:mustBindVars>
  <dql:answerKBPattern>
    <dql:kbRef rdf:resource="http://billdata/bill.daml"/>
  </dql:answerKBPattern>
  <dql:answerSizeBound>5</dql:answerSizeBound>
</dql:query>

<dql:answerBundle xmlns:dql="http://www.daml.org/2002/10/dql-syntax#"
                  xmlns:var="http://www.daml.org/2002/10/dql-variables#">
  <dql:queryPattern>
    <rdf:RDF>
      <rdf:Description rdf:about="#Bill">
        <has-father rdf:resource="http://www.daml.org/2002/10/dql-variables#f"/>
      </rdf:Description>
    </rdf:RDF>
  </dql:queryPattern>
  <dql:continuation>
    <dql:none/>
  </dql:continuation>
</dql:answerBundle>


Q: (has-father Bill ?f)
   may-bind ?f (or don't-bind ?f)
A: One answer (with no binding for ?f)

<dql:query xmlns:dql="http://www.daml.org/2002/10/dql-syntax#"
           xmlns:var="http://www.daml.org/2002/10/dql-variables#">
  <dql:queryPattern>
    <rdf:RDF>
      <rdf:Description rdf:about="#Bill">
        <has-father rdf:resource="http://www.daml.org/2002/10/dql-variables#f"/>
      </rdf:Description>
    </rdf:RDF>
  </dql:queryPattern>
  <dql:mayBindVars>
    <var:f/>
  </dql:mayBindVars>
  <dql:answerKBPattern>
    <dql:kbRef rdf:resource="http://billdata/bill.daml"/>
  </dql:answerKBPattern>
  <dql:answerSizeBound>5</dql:answerSizeBound>
</dql:query>

<dql:answerBundle xmlns:dql="http://www.daml.org/2002/10/dql-syntax#"
                  xmlns:var="http://www.daml.org/2002/10/dql-variables#">
  <dql:queryPattern>
    <rdf:RDF>
      <rdf:Description rdf:about="#Bill">
        <has-father rdf:resource="http://www.daml.org/2002/10/dql-variables#f"/>
      </rdf:Description>
    </rdf:RDF>
  </dql:queryPattern>
  <dql:answer>
    <dql:binding-set>
    </dql:binding-set>
  </dql:answer>
  <dql:continuation>
    <dql:none/>
  </dql:continuation>
</dql:answerBundle>


Q: (has-father ?p ?f)
   must-bind: ?p ?f
A: One answer for each known father

<dql:query xmlns:dql="http://www.daml.org/2002/10/dql-syntax#"
           xmlns:var="http://www.daml.org/2002/10/dql-variables#">
  <dql:queryPattern>
    <rdf:RDF>
      <rdf:Description rdf:about="http://www.daml.org/2002/10/dql-variables#p">
        <has-father rdf:resource="http://www.daml.org/2002/10/dql-variables#f"/>
      </rdf:Description>
    </rdf:RDF>
  </dql:queryPattern>
  <dql:mustBindVars>
    <var:p/>
    <var:f/>
  </dql:mustBindVars>
  <dql:answerKBPattern>
    <var:kb/>
  </dql:answerKBPattern>
  <dql:answerSizeBound>5</dql:answerSizeBound>
</dql:query>

<dql:answerBundle xmlns:dql="http://www.daml.org/2002/10/dql-syntax#"
                  xmlns:var="http://www.daml.org/2002/10/dql-variables#">
  <dql:queryPattern>
    <rdf:RDF>
      <rdf:Description rdf:about="http://www.daml.org/2002/10/dql-variables#p">
        <has-father rdf:resource="http://www.daml.org/2002/10/dql-variables#f"/>
      </rdf:Description>
    </rdf:RDF>
  </dql:queryPattern>
  <dql:answer>
    <dql:binding-set>
      <var:p rdf:resource="#Bill"/>
      <var:f rdf:resource="#Joe"/>
      <var:kb rdf:resource="http://geneology.com/jones.daml"/>     
    </dql:binding-set>
  </dql:answer>
  <dql:answer>
    <dql:binding-set>
      <var:p rdf:resource="#Joe"/>
      <var:f rdf:resource="#Frank"/>
      <var:kb rdf:resource="http://geneology.com/jones.daml"/>     
    </dql:binding-set>
    <dql:answerPatternInstance>
      <rdf:RDF>
        <rdf:Description rdf:about="#Bill">
          <has-father rdf:resource="#Joe"/>
        </rdf:Description>
      </rdf:RDF>
    </dql:answerPatternInstance>
  </dql:answer>
  <dql:continuation>
    <dql:termination-token>
      <dql:none/>
    </dql:termination-token>
  </dql:continuation>
</dql:answerBundle>


Q: (has-father ?p ?f)
   must-bind ?p, may-bind ?f (or don't-bind ?f)
A: One answer for each known person

<dql:query xmlns:dql="http://www.daml.org/2002/10/dql-syntax#"
           xmlns:var="http://www.daml.org/2002/10/dql-variables#">
  <dql:queryPattern>
    <rdf:RDF>
      <rdf:Description rdf:about="http://www.daml.org/2002/10/dql-variables#p">
        <has-father rdf:resource="http://www.daml.org/2002/10/dql-variables#f"/>
      </rdf:Description>
    </rdf:RDF>
  </dql:queryPattern>
  <dql:mustBindVars>
    <var:p/>
  </dql:mustBindVars>
  <dql:mayBindVars>
    <var:f/>
  </dql:mayBindVars>
  <dql:answerSizeBound>5</dql:answerSizeBound>
</dql:query>


<dql:answerBundle xmlns:dql="http://www.daml.org/2002/10/dql-syntax#"
                  xmlns:var="http://www.daml.org/2002/10/dql-variables#">
  <dql:queryPattern>
    <rdf:RDF>
      <rdf:Description rdf:about="http://www.daml.org/2002/10/dql-variables#p">
        <has-father rdf:resource="http://www.daml.org/2002/10/dql-variables#f"/>
      </rdf:Description>
    </rdf:RDF>
  </dql:queryPattern>
  <dql:answer>
    <dql:binding-set>
      <var:p rdf:resource="#Bill"/>
      <var:f rdf:resource="#Joe"/>
    </dql:binding-set>
    <dql:answerPatternInstance>
      <rdf:RDF>
        <rdf:Description rdf:about="#Bill">
          <has-father rdf:resource="#Joe"/>
        </rdf:Description>
      </rdf:RDF>
    </dql:answerPatternInstance>
  </dql:answer>
  <dql:answer>
    <dql:binding-set>
      <var:p rdf:resource="#Joe"/>
      <var:f rdf:resource="#Frank"/>
    </dql:binding-set>
    <dql:answerPatternInstance>
      <rdf:RDF>
        <rdf:Description rdf:about="#Joe">
          <has-father rdf:resource="#Frank"/>
        </rdf:Description>
      </rdf:RDF>
    </dql:answerPatternInstance>
  </dql:answer>
  <dql:answer>
    <dql:binding-set>
      <var:p rdf:resource="#Bill"/>
    </dql:binding-set>
    <dql:answerPatternInstance>
      <rdf:RDF>
        <rdf:Description rdf:about="#Bill">
          <has-father rdf:resource="http://www.daml.org/2002/10/dql-variables#f"/>
        </rdf:Description>
      </rdf:RDF>
    </dql:answerPatternInstance>
  </dql:answer>
  <dql:continuation>
    <dql:termination-token>
      <dql:none/>
    </dql:termination-token>
  </dql:continuation>
</dql:answerBundle>


If C1 is a Seafood Course and W1 is a drink of C1, what color is W1?
P: (type C1 Seafood-Course) (drink C1 W1)
Q: (has-color W1 ?x)
   must-bind ?x
A: White


<dql:query xmlns:dql="http://www.daml.org/2002/10/dql-syntax#"
           xmlns:var="http://www.daml.org/2002/10/dql-variables#">
  <dql:premise>
    <rdf:RDF>
      <rdf:Description rdf:about="#C1">
        <rdf:type rdf:resource="#Seafood-Course"/>
        <drink rdf:resource="#W1"/>
      </rdf:Description>
    </rdf:RDF>
  </dql:premise>
  <dql:queryPattern>
    <rdf:RDF>
      <rdf:Description rdf:about="#W1">
        <has-color rdf:resource="http://www.daml.org/2002/10/dql-variables#x"/>
      </rdf:Description>
    </rdf:RDF>
  </dql:queryPattern>
  <dql:mustBindVars>
    <var:x/>
  </dql:mustBindVars>
  <dql:answerKBPattern>
    <dql:kbRef rdf:resource="http://ontolingua.stanford.edu/wines.daml"/>
  </dql:answerKBPattern>
  <dql:answerSizeBound>5</dql:answerSizeBound>
</dql:query>

<dql:answerBundle xmlns:dql="http://www.daml.org/2002/10/dql-syntax#"
                  xmlns:var="http://www.daml.org/2002/10/dql-variables#">
  <dql:queryPattern>
    <rdf:RDF>
      <rdf:Description rdf:about="#W1">
        <has-color rdf:resource="http://www.daml.org/2002/10/dql-variables#x"/>
      </rdf:Description>
    </rdf:RDF>
  </dql:queryPattern>
  <dql:answer>
    <dql:binding-set>
      <var:x rdf:resource="#White"/>
    </dql:binding-set>
    <dql:answerPatternInstance>
      <rdf:RDF>
        <rdf:Description rdf:about="#W1">
          <has-color rdf:resource="#White"/>
        </rdf:Description>
      </rdf:RDF>
    <dql:answerPatternInstance>
  </dql:answer>
  <dql:continuation>
    <dql:termination-token>
      <dql:none/>
    </dql:termination-token>
  </dql:continuation>
</dql:answerBundle>