View source for PrF UG queries chain queries

__NOTOC__
== Chaining Multiple Queries ==

{{PrF_UG_TOC_queries}}<div id='prf_ug'>

Queries saved in the Query Library can be used as matching values
for slots of type Instance.
When you do this, the resulting query looks for instances
where the slot value is a search result for the specified query.

Often, when you need to create a query of this type,
you will look at a class that has a slot of type Instance
and want to know which of those instances have a certain property.
When you create the combined query,
you need to create the query for the property first,
and then create the query for the class.

For example, the query "Articles whose Authors are highly paid"
looks for instances of the Class <b>Article</b> whose value at the slot <i>author</i>
is also a valid result of the query "People with salary greater than 100,000".

<div>[[Image:PrF_UG_queries_people_highly_paid.png|frame|none|
       People with salary greater than 100,000]]</div>


<div>[[Image:PrF_UG_queries_articles_whose_authors.png|thumb|none|600px|
       Articles whose Authors are highly paid]]</div>

You do not have to use a slot in either query.
If you just use a class,
you will find all instances of that class and its subclasses.

To create a query of this type,
you need to make sure the two queries satisfy the following:

<ul class='a'>
  <li><p>
    The slot value for Query B,
    the query that contains another query,
    must be one of the following:
    </p>

  <ul>
    <li><p>
      a slot of type Instance
      </p>
  
    <li><p>
      empty (in this case, you must select a class)
      </p>
  </ul>

  <li><p>
    For the final chained query to be meaningful,
    Query A (the query that will be used inside the other query)
    must have results that intersect the possible inputs for Query B.
    If Query A has a slot, the domain for the slot
    should intersect the Allowed Classes for the slot of type Instance in Query B.
    If Query A does not have a slot, the subclasses of the class in Query
    should intersect the subclasses of the Allowed Classes
    for the slot of type Instance in Query B.
    </p>
</ul>

To create a query of this type

<ol class='a'>
  <li><p>
    [[PrF_UG_queries_create_query|Create]] an initial query.
    </p>

  <li><p>
    [[PrF_UG_queries_saving_query|Save]] this query
    in the [[PrF_UG_queries_query_library|Query Library]].
    </p>

  <li><p>
    Clear the current query.
    </p>

  <li><p>
    Select the Class and/or Slot you want for the second query.
    </p>

  <li><p>
    Select <b>contains</b> or <b>does not contain</b> from the menu.
    </p>

  <li><p>
    Click the <b>Add Query</b>
    ([[Image:PrF_UG_queries_query.gif|queries_query]]) button.
    </p>
    <p>
    <b>Note:</b>
    You may have some trouble getting this to display.
    If you do, try switching to another tab and then returning to the Queries Tab.
    If that doesn't work, try retrieving the "Articles whose authors are highly paid" query
    from the Query Library, then clearing it and recreating your query.
    You may still have to switch to another tab after you have entered your slot,
    but this should work.
    </p>

  <li><p>
    A <b>Pick Query</b> dialog displays the saved queries.
    </p>
    <div>[[Image:PrF_UG_queries_pick_query.png|frame|none|
           Pick Query dialog]]</div>

  <li><p>
    Select the query you want and click OK.
    </p>
</ol>

You can also [[PrF_UG_queries_create_complex_query|combine]] chained queries
with other queries.


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