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Re: what is LDOM? (was Re: example of recursive shapes)

From: Peter F. Patel-Schneider <pfpschneider@gmail.com>
Date: Sun, 25 Jan 2015 17:20:48 -0800
Message-ID: <54C59670.4060708@gmail.com>
To: Holger Knublauch <holger@topquadrant.com>, public-data-shapes-wg@w3.org
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Indeed the wording you point out is in the document, but it does not speak
to the ability of LDOM to handle recursion. It simply says that LDOM uses
procedural recursion to handle nesting. Nesting is very different from
recursion.

Yes, I think that a definition of LDOM is needed before it can be
appropriately evaluated by the working group.  Without a definition of LDOM
it is not possible to determine just what basic facilities it provides.

peter




On 01/25/2015 02:38 PM, Holger Knublauch wrote:
> Peter,
> 
> you started this discussion by claiming that LDOM cannot handle
> recursion. If you had done a text search for "recurs" you would have
> found
> 
> ldom:violatesConstraints a ldom:Function ; rdfs:subClassOf ldom:Functions
> ; rdfs:label "violates constraints" ; rdfs:comment "Checks whether a
> given resource (?arg1) fulfills all constraints defined for a given class
> (?arg2) or its superclasses. This creates a (possibly recursive) LDOM
> constraint checker." ;
> 
> and
> 
> "The SPARQL query behind the ldom:OrConstraint uses a built-in helper
> function ldom:violatesConstraints to recursively evaluate the nested
> shapes."
> 
> This particular information *was* already there.
> 
> You seem to be asking for a formal spec, i.e. the end result of the whole
> WG, *before* we can even start discussing it?
> 
> Holger
> 
> 
> On 1/26/15, 12:25 AM, Peter F. Patel-Schneider wrote: This is not just a
> matter of details.  It now appears that there are aspects of LDOM that
> are not touched on in the information that has been sent out. Without
> comprehensive information on what LDOM is, discussion of it in the 
> working group is not going to be useful.
> 
> peter
> 
> 
> On 01/24/2015 06:34 PM, Holger Knublauch wrote:
>>>> The "magic" is in the SPARQL function ldom:violatesConstraints
>>>> which has to be implemented by LDOM-compliant SPARQL engines. It
>>>> recursively calls another LDOM engine with another node and shape
>>>> as starting points. This function can also be used as entry point
>>>> into the API, and could become one of the Use Cases in the
>>>> requirements document.
>>>> 
>>>> Yes, details will become clearer once written up.
>>>> 
>>>> Holger
>>>> 
>>>> 
>>>> On 1/25/2015 12:33, Peter F. Patel-Schneider wrote: I still don't
>>>> see how LDOM can handle this example if it is all supposed to be
>>>> translatable into SPARQL queries.  Perhaps a definition of LDOM
>>>> will make this clear, but I don't think that one has been presented
>>>> as of yet.
>>>> 
>>>> peter
>>>> 
>>>> 
>>>> On 01/24/2015 06:23 PM, Holger Knublauch wrote:
>>>>>>> On 1/25/2015 11:48, Peter F. Patel-Schneider wrote:
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>>>>>>>> 
>>>>>>>> I can't tell whether this does or not, as there appears to
>>>>>>>> be a missing bit after ldom:predicate.
>>>>>>> Ok, the missing bit was a left-over from when I noticed that
>>>>>>> we don't have a better syntax for owl:hasValue. I have
>>>>>>> meanwhile added a new template using ldom:hasValue to improve
>>>>>>> readability (not that it matters for the recursion though):
>>>>>>> 
>>>>>>> ex:Polentoni a rdfs:Class ; # or ldom:Shape, or nothing 
>>>>>>> ldom:property [ ldom:predicate ex:livesIn ; ldom:hasValue 
>>>>>>> ex:NorthernItaly ; ] ; ldom:constraint [ a
>>>>>>> ldom:ShapeConstraint ; ldom:predicate ex:knows ; ldom:all
>>>>>>> ex:Polentoni ; ] .
>>>>>>> 
>>>>>>>> However, I don't think that it could, as least so far as I 
>>>>>>>> understand LDOM, as the class definition below appears to
>>>>>>>> require that ex:Polentoni is asserted on some individuals,
>>>>>>>> and the point of the example is that there are no
>>>>>>>> assertions involving ex:Polentoni in the input.
>>>>>>> No, this is a misunderstanding. When ldom:all is used, it
>>>>>>> will simply check whether the instance matches all conditions
>>>>>>> specified by the given class/shape. The rdf:type triple is
>>>>>>> not restricted by the shape, therefore no rdf:type needs to
>>>>>>> be present on the valid instances.
>>>>>>> 
>>>>>>>> If LDOM does work by doing recognition, then this should
>>>>>>>> be highlighted.
>>>>>>> I have added a sentence
>>>>>>> 
>>>>>>> Note that the matching values do not have to be instances of
>>>>>>> the given shape, i.e. no <code>rdf:type</code> triple is
>>>>>>> required.
>>>>>>> 
>>>>>>> Needless to say the overall specification needs work to
>>>>>>> clarify and better explain these details - some of them are
>>>>>>> currently well hidden in the implementation (Turtle
>>>>>>> code/SPARQL queries).
>>>>>>> 
>>>>>>> HTH and thanks for the example. I hope we agree recursion is 
>>>>>>> covered. Holger
>>>>>>> 
>>>>>>> 
>>>> 
> 
> 
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Received on Monday, 26 January 2015 01:21:18 UTC

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