Re: rule proto-proposal

From: pat hayes (
Date: 05/30/01

>>>>>(2) A single semantics for one kind of language. We will have 
>>>>>multiple languages represented in RDF, e.g.
>>>>>UML (see  ) and it 
>>>>>would be nice if the rule language we
>>>>>design is able to deal with multiple languages at the same time.
>>>>Again, I have no idea what you mean. How can *a* (note singular) 
>>>>rule language deal with multiple languages? ("Deal with" in what 
>>>>sense? )
>>>Be able to compute the deductive closure of a single set of RDF 
>>>statements with respect to a set of rules.
>>Stefan, according to you there is no such thing as the deductive 
>>closure of a set of RDF statements. You have said earlier in this 
>>thread that RDF triples have no logical interpretation, and in this 
>>message you say that RDF is a datastructuring language. Concepts 
>>like 'deductive closure' only apply to languages with a proof 
>>theory. What are the inference rules of RDF?
>I meant the deductive closure of the Facts + Rules. Sorry for the sloppiness.
>RDF does not have inference rules, in the same way that a set of tuples has
>no inference rules. Together with a rule language (e.g. SQL) I might 
>have inference

Maybe we are still not following one another. As I understand your 
position, the rules themselves do not have a semantics (right?). So 
they are not *inference* rules, and it still seems to me not to make 
sense to speak of a deductive closure. In fact, if the RDF triples 
don't have a semantics (ie if RDF is a datastructuring language) then 
the triples are not even properly called 'facts'. A triple without 
any meaning assigned to it is just a datastructure, not a fact. It 
might be intended to represent a fact, or a picture, or a diagram, or 
a mathematical expression, or just about anything, or even nothing. 
Without a semantics, there is no way to tell.

>>>>And in any case what does it mean to say that there will be 
>>>>multiple languages "represented" in RDF? In the example in 
>>>> , the RDF graph is 
>>>>being used simply as a graph to encode a state diagram,
>>>>in a way that completely ignores the RDF semantics (such as it 
>>>>is). If that is 'representation', then RDF is just being used as 
>>>>a datastructuring language.
>>>If I store a statemachine in a database, do I ignore the logical 
>>>semantics of a database?
>>>Probably yes, but I can live with it and I guess other people can also.
>>I guess at this point we should just declare that we are working in 
>>different worlds. I feel like someone who is trying to design 
>>better cars, arguing with someone who insists that an internal 
>>combustion engine can be used to cook hamburgers. Of course you are 
>>free to you store a statemachine in a database, but it seems to me 
>>that the designers of the database language are then under no 
>>obligation to support you or accomodate to what you are doing. If 
>>you do things like that, you are on your own.
>If a database vendor wants to restrict in me what kind of data I'm 
>allowed to store in my database,
>I don't buy the database.

No, of course, but that is a different issue. You didn't say that you 
were storing *data about* a statemachine; you said you were storing 
the statemachine. That is what Melnik is doing, seems to me: he is 
using the 'data' not as data at all, but as an encoding for something 
entirely different. Now, one can do that, of course. You CAN use 
predicate logic syntax to encode musical notation (use depth of 
function nesting for pitch, the constant at the bottom of the term 
for length of note, and clause ordering to indicate time-sequence) 
but if you do that, then you have no legitimate complaint if a Prolog 
interpreter fails to handle key shifts, say. The Prolog isnt meant to 
be used that way, and that way of using the notation does not conform 
to its declared semantics. Similarly, if you take a relational 
assertion language and use it to encode finite-state transition 
diagrams, then you cannot complain if the rule processor fails to 
conform to the conventions of your idiosyncratic usage; and, more to 
the present point, the designer of the rule language is not obliged 
to consider such idiosyncratic uses. If people want to write 
arbitrary encodings with perfect freedom, then they should be writing 
code, not putting data  into datbases; and they can't expect to get 

>An example: look at
>These people are building an Ontology for representing business processes.
>This incorporates states, events, dynamics etc.
>Are you saying they are not allowed to express these concepts in an 
>ontology language

Of course not

>express it in RDF? (Actually, they use XML Schema).

Sure, though I think their chances of being able to do so in RDF are 
remote. [Added later: did you really mean *express* it in RDF? Or did 
you mean encode the datastructures of the ontology language in RDF? 
Of course they can do the latter, but that's not what I would call 
expressing the ontology in RDF.]

But look: there is a distinction between building an ontology in an 
ontology langauge, and constructing datastructures in a datastructure 
language. In the first case the language has a semantics; in the 
second case, it does not (or at any rate, if it does, it is a 
semantics about datastructures, not about the concepts in the 

>>>And yes, RDF is a datastructuring language.
>>Well, Stefan, that is not what the rest of the RDF community seem 
>>to be saying. I wish y'all would get your act together and come out 
>>with a single consistent story. If RDF is just a datastructuring 
>>language, then what has it got to do with the Semantic Web? And 
>>what advantages does it have over LISP (say), or XML ?
>It as consistent as every community where different people with 
>different opinions and different
>background try to work together.

That says nothing about the utility of RDF over XML (or LISP, for that matter).


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