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RE: WordNet modelling in Lemon and SKOS

From: Armando Stellato <stellato@info.uniroma2.it>
Date: Tue, 16 Apr 2013 11:33:22 +0200
To: "'Philipp Cimiano'" <cimiano@cit-ec.uni-bielefeld.de>, <public-ontolex@w3.org>
Message-ID: <018801ce3a85$71fa6620$55ef3260$@info.uniroma2.it>
Ahhh, ok! :D


From: Philipp Cimiano [mailto:cimiano@cit-ec.uni-bielefeld.de] 
Sent: martedì 16 aprile 2013 09.42
To: public-ontolex@w3.org
Subject: Re: WordNet modelling in Lemon and SKOS


Dear Armando, all,

 I think that actually all the issues you raised are important, so I would like to create one thread per topic as otherwise discussion becomes difficult in the light of too many topics.

So you will receive 5 emails from me along the day ;-)


Am 15.04.13 19:41, schrieb Armando Stellato:

Hi all,

First of all, thanks John for providing the example: through concrete examples it is easier to discuss!


A few comments (the same “disclaimer” from Elena holds for me: hope I didn’t miss anything from other discussions, and in case, sorry in advance).


1)      First of all (sorry a bit out of topic), I would ask for a clarification, so that I can apply the policy to my examples too: I see the “lemon:” prefix being used in many examples, and Lemon is an outcome of Monnet project. Is it also the definitive name (or a temporary name) we are giving to the model we are developing in this community group? I’ve been using “ontolex:” as a fictitious prefix in my examples, and just got “lemon” was being used by some of you, because those of you working on Monnet have started right from examples they already built in the original lemon. Sorry for asking what seems to be trivial, but I never got any definitive statement on this, so, better to realign late than never :-D 
Btw, what is written at the last row of:  <http://www.lemon-model.net/> http://www.lemon-model.net/ seems to confirm my hypothesis.

ok..back to the original topic. Consider that a few of these observations can actually be solved by completing the example, and do not necessarily clash with it (or, at least, do not clash with what has been already written, while I don’t know of what was thought for the rest).


2)      With respect to Wordnet (which has explicitly ordered senses per word, where I think this order originates – at least for some of the words – from frequencies in SemCor) the sense ordering is lost: the synsets are bound to the words by means of the sole listing of values, which in plain RDF is unordered.


3)      This is the most important observation: the use of lemon:sense . Together with lemon:reference, lemon:sense should realize the bridge from lexical entries to conceptual entities (of the domain ontology). Should we use it reach the conceptual entities (e.g. synsets) of the lexical resource AS WELL?. In terms of black-box compatibility, as we are modelling even conceptual info of lexical resources (e.g.  synsets in wordnet) through some RDF language (e.g. SKOS), the thing is legal (the rdfs:range of lemon:sense, providing it is wide enough, is respected), still I’m not sure we want that. Shortly, I’m not sure if we want to apply exactly the same 3-entities approach we are using for the lexicon-ontology model, to modelling solely a lexical resource.
Let’s make an example. We have myont: which is a domain ontology (where we have the entry myont:vomit) we are enriching with lexical content, possibly from wordnet. Then we have the necessity of representing a direct linking between some lexical entries (which may happen to be in wordnet or not) and the domain entities of myont.
We would have thus this example, which I derived from both the WordNet example, and the generic OntoLex example for enriching an ontology with lexical content: 

               a lemon:LexicalEntry
               lemon:sense <cat::2:29:0::>, <cat::2:35:0::> ;
               a lemon:LexicalSense ;
               lemon:reference <VerbSynset76400> .
               lemon:reference myont:vomit .

Note that I’ve cut from the original example, the triples which are non-useful to the discussion.

Actually, in writing this revised example, I’m not even sure if the two lemon:references should be put under the same sense umbrella, or I should have used two different senses. This is mainly because I’m not sure about the concept of “sense” here and what it represents. I see potential for confusion even by looking at the Elena/John emails, as she rightly asks about the use of skos:definition instead of lemon:definition. While I’m not addressing here the use of a property or the other, the answer by John, hinting at the fact that there could be two definitions, one for a sense, and one for a synset (and consider that there could be a definition for the element in the ontology), makes me wonder how many levels we should have!
Without delving too much in the appropriateness of this indirection for what concerns the lexicon-ontology interface, and considering the sole context of the representation of Wordnet (thus just the lexicon perspective), to me the path from the LexicalEntry to the Synset is too long. In wordnet we just say that a word is linked to a synset: period (modulo the addition of an ordering). In particular, “sense” is a relation which just tells me that synsetX is the i-th sense of word Y (and there’s a many-to-many rel between words and synsets).

…and this brings me back to our first discussions about the choice of the term sense, when referring to the path from lexical entries to ontology elements and about the nature of “elements-in-the-middle”.
In my view (to avoid terminological problems, I focus here on the path between entities, and do not name the linking properties at all, so pls consider all the arrows here have properties behind, in particular lemon:sense and lemon:reference), when considering a mapping between a lexical resource such as Wordnet, and an ontology, I would have seen such a path:
LexicalEntry --> Synset --> OntologyResource
where, without using WordNet, the path would have been:
LexicalEntry --> [] --> OntologyResource
with [] a blanknode creating this gluing between them.
The second line is identical to what we have done until now and what has been written in the examples in the “Specification of Requirements/Lexicon-Ontology-Mapping”. In particular, the blanknode is an instance of that element-in-the-middle (see: “Need for an object between Lexical Entry and Ontology”) which still has not a name (and maybe it does not need to have, see point 4 below). The first line is thus my interpretation of how WordNet would have fit into that general template (different from John’s example).
So, my idea would be to not replicate the complex lexicon-ontology linking inside WordNet itself, and have instead a direct linking between lexical entries and Synsets, and have THEN, outside of WordNet, a further link to an ontology element. If you look at the two rows above (and how the WordNet case fits the general case), this is pretty elegant, and does not introduce a further level of indirection which appears not necessary. Plus, with this method, the link from synsets to ontology elements is a necessary step to instantiate the path above, while in the other case, you should introduce it as an additional (and probably redundant) triple. You can see it in fact in the turtle code above, which I modelled following both the general example in “Specification of Requirements/Lexicon-Ontology-Mapping” and John’s example on WordNet: there, VerbSynset is a separate entity from myont:vomit. Actually, in that view, WordNet would become a separate “ontology” which could then be mapped to a domain ontology, instead of taking all the benefit of being seen as a lexical resource that can be used, seamlessly within our model, to enrich a domain ontology.

4)      IMHO, we should coin a specific vocabulary for each element of the lexicon model, and then inherit (where appropriate) from SKOS/SKOSXL, to distinguish such elements which belong only to a lexical resource from those of any generic KOS. In the wiki, John wonders if what I called “SemanticIndex” is not a skos:Concept, and I reply: “yes it is, in fact my proposal is that our vocabulary for describing lexical resources can inherit from the SKOS/SKOS-XL one”. If you look at the example, even John did this, as the LexicalForm is nothing different from a skosxl:Label (where lemon:writtenRep could be replaced by skosxl:literalForm) though it may be worth creating a dedicated class. I would thus suggest:
LexicalForm rdfs:subClassOf skosxl:Label 
but to use skosxl:literalForm instead of lemon:writtenRep

maybe, in this specific case, we can even not reinvent a name, and totally reuse the skosxl:Label, which after all is not so bad and pretty fitting our necessities… (as it is already related to something specifically thought for language).

On the contrary, for LLD, I would necessarily restrict the class skos:Concept to the class of elements which we expect to host things like the WordNet Synset class. You can see my sample extension-point above in the wiki (“Examples of Modelling in RDF (Alternative approach)”), though by now mean I suggest <SemanticIndex> (that was a placeholder, taken from a previous work), but in any case I think “Sense” is not appropriate (lemon:sense well evokes the sense relation, while I don’t like to see a class of “Senses”, that is, to me being a sense is more a role in a given relationship, than a intrinsic property of an object).

a.       While I think that a more-specific-than-skos:Concept class would be welcome for Lexical Linked Data (such as WordNet), and thus put in the middle of the: LexicalEntry --> ??? --> OntologyResource  template, I’m not sure that the lemon:sense (first arrow) should be necessarily restricted to it. John’s use of skos:Concept in the middle suggested me that even a generic well-lexicalized KOS could be used for providing LexicalEntries and Senses to enrich an ontology. However, I’m still thinking about it…

5)      Another thing which comes to my mind, quite out of the WordNet example, but not without consequences for it... What should be, in general, the expected modelling behaviour when we have two terms which coincide, but the syntactic use of which can follow different paths?
E.g., suppose we have a term with three senses. In the context of these senses, with two of them (say 1 and 2), the term has exactly identical variations (declensions for nouns pronouns and adjectives and conjugations for verbs ), and maybe other information in common (think about etymology!), while for the third sense, this may show differences in the variations (e.g. a noun would have a different plural form, or a verb has a different form in only one tense, when used with that sense). Should we model them as 3 different lexical units, or should we agglomerate the two identical ones into one LexicalEntry, and link it to senses 1 and 2?
This seems to be not related to modeling WordNet in the specific, because variations, declinations etc.. are out of WordNet. However, this may affect a model trying to reuse WordNet enriched with further information… Thus it’s important when we consider how a WordNet modelling could be ported inside an extended framework with no risk of inconsistency.

I just thought about a solution for this: if we allow for skosxl:Labels to be directly attached to Synsets (or whatever it is the superclass for them), and then we state the following rule:
LexicalEntry -> lemon:canonicalForm -> skosxl:Label
LexicalEntry -> lemon:sense -> <asynset>
skosxl:Label -> ???:sense (whatever it is called) -> <asynset>

this would allow for the complex structure we expect in general, but also allow for a more neutral fit of WordNet. In fact, instead of having the third triple as inferred, for WordNet we could just explicitly mention the third one, and do not put potentially compromising information (which, in any case, is out of WordNet, as noted by John in his reply to Elena).
The “???:sense (whatever it is called)” could even be lemon:sense itself, providing that its range is LexicalEntry+skosxl:Label.
However, I still have to think more about that…


One more thing, observation in point 2 above made me think once more that we should be clearer in our objectives:

Fact: since we have to model ontology-lexicon interfaces, and there isn’t much out there for representing lexical info (limited to RDF, I mean); we have thus to provide a model for the linguistic part, before “attaching” it to the ontology part. Now, the objective could be:


1)      We want to model lexical knowledge, and we give a model for this. WordNet may be (in part) more fine grained than our model…no big trouble, WordNet is WordNet, and our model is our model… we’ll be missing those details..

a.       A slightly different interpretation of the above: we want to model lexical knowledge, AND we decide WordNet IS the model (at least for the monolingual word-description needs..I leave out FrameNet et similia from this context of discussion). No big deal with other alternative resources to WordNet..

2)      We want to model existing lexical resources. Thus WordNet, as well as other resources (maybe differently organized) are all important


Obviously, there are endless colours in the middle of the above, as we could be in case 1 or 2, and still think WordNet is so important that it has to be fully covered (also because, in this way, Princeton could decide to natively output each new release of WordNet in RDF too according to our model).






P.S: I’ve brought a couple of small fixes to the page:  <http://www.w3.org/community/ontolex/wiki/Specification_of_Requirements/Lexicon-Ontology-Mapping#Summary_on_Requirements_on_the_Lexicon-Ontology-Mapping_.28Synthesis_by_PC.29> http://www.w3.org/community/ontolex/wiki/Specification_of_Requirements/Lexicon-Ontology-Mapping#Summary_on_Requirements_on_the_Lexicon-Ontology-Mapping_.28Synthesis_by_PC.29 which we already discussed 2 or 3 meetings ago.



From: johnmccrae@gmail.com <mailto:johnmccrae@gmail.com>  [mailto:johnmccrae@gmail.com] On Behalf Of John McCrae
Sent: venerdì 12 aprile 2013 16.10
To: public-ontolex
Subject: WordNet modelling in Lemon and SKOS


Hi all,


Here is the proposed modelling of WordNet as lemon and SKOS (using skos:Concept for synsets)


 <http://www.w3.org/community/ontolex/wiki/Specification_of_Requirements/Linked_Data#Example:_WordNet_as_lemon-SKOS> http://www.w3.org/community/ontolex/wiki/Specification_of_Requirements/Linked_Data#Example:_WordNet_as_lemon-SKOS


Any comments?




Prof. Dr. Philipp Cimiano
Semantic Computing Group
Excellence Cluster - Cognitive Interaction Technology (CITEC)
University of Bielefeld
Phone: +49 521 106 12249
Fax: +49 521 106 12412
Mail: cimiano@cit-ec.uni-bielefeld.de <mailto:cimiano@cit-ec.uni-bielefeld.de> 
Room H-127
Morgenbreede 39
33615 Bielefeld
Received on Tuesday, 16 April 2013 09:34:27 UTC

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