Re: modelling issue?

On Oct 5, 2009, at 2:31 PM, Paola Di Maio wrote:

> Pat,
> thanks for reply
>
> If we consider for a moment the semantic web as an 'enterprise',  
> uncertainties = risks , resolving these issues/ possibilities may  
> result into  overheads and difficult management decision (which the  
> majority of managers cannot really deal with hence set aside for  
> future generations to handle)
>
> briefly, below
>
>
>
> Well, this may be partly caused by the various terminologies in use,  
> eg RDF "property" is sometimes called a "relation" and RDFS/OWL  
> "class" is sometimes (confusingly) called "property" and sometimes  
> called "set".
>
> this alone would be enough to cause the average working ontologists  
> some headache (possibly leading onto bigger existential questions)  
> -  (semantic consistency anyone? - glad to see the workshop coming up)
>
>
> No, there is no actual rule. In general, its often a good idea to  
> provide all information that you have available, so if indeed you  
> know the domain and range then you might as well write that down. In  
> doubt, it is fine to specify a more vaguely defined superclass: that  
> is always harmless and might be useful.
>
>
> sounds v heuristic

Well yes, and it is so, inevitably. Particular domains or contexts  
might have more concrete rules of thumb/management, but RDF is  
supposed to be the interlingua which serves all masters, so it cannot  
presume in this area.

>
>
>>
>>
>> class:relation:class
>>
>>  but also
>> class:attribute:value
>>
>> Of this i would like some confirmtion (is this right?
>>
>> No. Or at any rate, not if I am following you. First, the first  
>> item (subject) of the triple isn't necessarily a class.
>>
>> okay, I have always assumed that the subject *is* a class, any  
>> hints as to what are my options?
>> or what chapter of the book/tutorial I can find the relevant info?
>
> Well, there is no info because there are no constraints. The subject  
> of an RDF triple can be anything. If you can refer to it using a  
> URI, then it can be a subject, i.e. you can say something about it.
>
>
> and if not?

Well, anything CAN be referred to by a URI. If you own the URI, then  
it is up to you to specify what it is supposed to refer to, of course.  
Publishing some RDF or OWL which uses it is one way to do that :-)

>
>>
>> scroll down to FIG 7
>
> Again. I am afraid that I have no sure idea what this diagram is  
> supposed to mean. I will however make some guesses, based in part on  
> your translation. Correct me if I am wrong.
>
> The way I see it (since we are all mere interpreters) all the boxes  
> are 'things' (I really like that view of the world)
> and all the lines are relations into things
>
> Note: I agree that describing the world is messy, and that pointing  
> to it should be simpler, but 'pointing to things'
> is by no means trivial. I have recently come across 'organisational  
> semiotics' (R Stamper) and wonder if there is anything to learned  
> there. Got some easy example, of where we think we are pointing to  
> something, but people see something else
> (the finger and the moon example is one of them)

There are libraries written about semiotics and how symbols get  
interpreted. But really, RDF is way simpler than almost any of this.

>
> Take the example of
> Organization --Has -- Affiliated_Person, which is a long slightly  
> curved line on the LH side of the diagram. Does this mean that  
> things in the Organization class, i.e. organizations, all have an  
> affiliated person who is a member of the class Affiliated_Person?  
> Because if so, this is not adequately represented by a single RDF  
> triple.
>
> ah, that sounds possible, so that would have to be many triples?

It would be more than one, since you have to say that the property  
applies to things in one class (using rdfs:domain, for example) and  
takes values in the other (using rdfs:range), and that is two triples  
already. You might want more, it depends on exactly what you want to  
say.

> That takes me to the 'concatenation question' - is it true that a  
> thing that is a subject in a triple cannot be
> anything else in another triple in the same vocabulary?

No, that is not true. Any URI can be used in any position in any  
triple in any ontology. It is fine for it to be the subject of one and  
the object (or even the property) of another.

> If so, how can we concatenate and/or merge vocabularies (apologies  
> if the question is too big/open)
>
>
>
>>
>> So, to sum up, after realising that we can use RDF equall to triplify
>>
>> ORGANISATION   HAS     CONTACDETAILS
>> (class)                   rel        (class)
>>
>
> This says that the HAS relationship holds between the actual  
> classes, not between the elements of the classes. Is this really  
> what you intend to say?
>
> in the example above  yes

Hmm. So you are saying that the actual class called ORGANISATION -  
that is one single class - bears the relation called REL to one other  
single thing, also a class, called CONTACDETAILS. So there are exactly  
two things being referred to here, and their status as classes is  
irrelevant. Is this really correct? To push the point home: nothing  
would follow from this about any particular organization having  
anything. It does not follow from this that a member of the class  
ORGANISATION has a contact detail. Is that right?

> , the example below I am looking at the stuff in the box (relation  
> between the class and its elements)
>
>>
>> but also
>>
>> ORGANISATION     IS        OFTYPE

A 'type'  is a class, actually. Being in the class = having the type,  
just a different form of words. RDF actually uses the word "rdf:type"  
to relate a class member/instance to its class. So a TYPE of  
organizations is a subclass of the class ORGANIZATION, the class of  
all organizations.

>>
>> or
>> ORGANISATION     HAS    WEBSITE

Again, that sounds to me like it is intended to be saying that every  
organization in ORGANISATION has a website. If this is about the  
class, it says that there is a *single* website for *all*  
organizations, or maybe for the class called ORGANISATION.

Pat


>>
>>
>>
>>
>> is this 'versatility' of using RDF in the same way for either/both
>>
>> a) what is referred to as an RDF weakness?
>> b) never been thought of as a problem when modelling data?
>> c) related to the intensional /extensional discussion referred to  
>> as above?
>>
> PDM

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