A question about PM with a partial list

[Tareq Alkhaldi]

Hi all,

Is there a way to use the PM to match a partial list as the following?

Atomspace has this:

(EvaluationLink

    (PredicateNode "pulled@463a5d30-1733-48bc-b188-cb1fcd1d3ee0")

    (ListLink

        (ConceptNode "James@c597a7ec-60ab-429d-b003-4782200c7a91")

        (ConceptNode "pudding@f797c773-b58a-4136-8bad-74b4ad399c63")

        (ConceptNode "all@3f71ac77-ef99-4499-883d-2ae3332fdb6a")  ;;;;; This may or may not exist

    )

)

Pattern I want to match is:

(BindLink

  (VariableList

     (VariableNode "$X")

     (VariableNode "$Y")

  )

  (EvaluationLink

     (VariableNode "$X")

     (ListLink

        (ConceptNode "James@6c0671a2-1b11-4dd9-a787-d27d7779a0c8")

        (VariableNode "$Y")

     )

  )

  (VariableNode "$Y")

)

How can I match that without having to add another variable after "$Y" in the list, knowing that the (ConceptNode "all@...") may not always be there.

Can this be done?

Thanks

[Linas Vepstas]

Hi Tareq,

Currently, the only way to do this is is to write two different patterns, one that searches for three words, and one that searches for two.

Another possibility is to use a GlobNode instead of a VariableNode, this will accept sequences of neighboring words, as one.  However, this might not be what you want: the output of a glob is a list.

You do ask an interesting question: it would be nice to have this kind of matching.  Currently, VariableNode must match exactly one item, and GlobNode must match one or more.   A "MaybeNode" that matches zero or one, and a "StarNode" that matches zero or more could be useful.  .. But these don't exist, yet.  Might not be hard to add ... 

--linas

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[Tareq Alkhaldi]

Hi Linas,

Okay, I started adding the StarNode variable, but I have a question. So StarNode should work exactly like GlobNode except that it can accept a zero, right? What about something that will match zero or more but not necessarily in order? For example to match all the nodes in the pattern, and throw all the unmatched nodes (in any location) on that level in the target side to this variable. It's kind of "AllUnmatchedStuffNode" (for lacking a better name).

--linas

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[Linas Vepstas]

Hi Tareq,

You can probably implement StarNode as a minor variation on the current GlobNode code. By the way, that code is here: https://github.com/opencog/atomspace/blob/master/opencog/query/PatternMatchEngine.cc#L227-L288

and specifically, here: 

https://github.com/opencog/atomspace/blob/master/opencog/query/PatternMatchEngine.cc#L255-L261

So, to implement star-node, all you need to do is to change line 257 to say "if (is_glob and tc)" and set is_glob to false when matching star nodes.

The inverted match is here: 

https://github.com/opencog/atomspace/blob/master/opencog/query/Recognizer.cc#L218-L254 

I don't think you need the inverted match in what you are doing.

Re: ordered vs unordered:  this is already handled automatically. If your data is in an ordered link, then the comparison to the pattern will always be ordered. If the data and pattern are unordered links, then all possible permutations will be explored.  One of those permutations will put everything "unknown" next to each-other, where the star node can pick them up.  

There's even a unit test, somewhere, checking that globnode works with unorderded links. so it should work automatically ... 

So you do not need to write any extra code to handle the "match everything left over". Unless you mean... Hmm. Unless you mean this:

(ListLink    ; notice this is an ordered link!

    (ConceptNode "a")

    (ConceptNode "b")

    (StarNode "var")

    (ConceptNode "p")

    (ConceptNode "q")

    (StarNode "var")

    (ConceptNode "y")

    (ConceptNode "z"))

and you want everything dumped into one big bag.  Because right now, the way pattern matching is defined, the above will match only if the stuff in the first location is exactly identical to the stuff in the second location.

If you want everything i a big bag, it would be better to use two vars, and consolidate them into one, after the matching is done.

--linas

[Tareq Alkhaldi]

Hi Linas,

Thanks, I'll get to it once I'm done with the current phase of homeworks, reports and a big report coming up for school.

You're right about what I thought, I thought I could have an orderedList (a, b, c, d.. etc), match (a, d) and throw everything else into another variable. For now I'll try the StarNode if it works with what I'm trying to do.

Thanks