Re: [RIF] Extensible Design

Gerd Wagner wrote:
>>> 3) Data literals, object names, function symbols
>>> and predicate symbols may be typed. Using suitable
>>> predicate/atom types, this allows to represent RDF 
>>> and OWL rules directly (and not only via a "query 
>>> interface").
>> Could you elaborate on why typing of function and predicate 
>> symbols is required for representation of RDF (rules)?
> 
> With "RDF" I was, in fact, refering to RDF+RDFS where 
> you have typed predicate symbols in the form of domain
> and range restricted properties.

Yes and no. Yes you can declare rdfs:domain/range of properties but they 
just entail new rdf:type inferences. That doesn't really give you a type 
system in the programming language sense since RDF resources can have 
multiple types, such declarations don't restrict where properties can be 
applied.

Clearly with OWL you can say that two classes are disjoint and then you 
can start to use domain/range as restrictions but you are not forced to 
do so.

> I see your point that on the level of pure RDF you
> prefer to have no typing. But as Hassan has pointed
> out, most rule/programming languages used in practice
> are typed (probably because it pays to exploit the
> computational benefits of typing).

 From a data modelling point of view the notion that a resource can have 
multiple types, including types you don't yet know anything about, is 
extremely useful. A significant part of the benefits we gain from use of 
RDF derives from the extensibility given by this semi-structured, open 
world approach. A strongly typed rule language would lose that benefit.

Clearly RIF will include support for typed predicates/functions because 
many of the systems which might interchange rules do use types. But that 
typing should remain optional (as it currently is in the condition 
language proposal).

[There, I managed to avoid getting side-tracked by pointing out the 
benefits and successes of weakly typed programming languages such as 
modern scripting languages ... whoops ...]

Dave

Received on Friday, 5 May 2006 10:45:49 UTC