Re: About ticle

Hi,

Following this post, I have some quite urgent questions to the group. I
hope you can answer them quickly and precisely. Please note that I am
biased towards RDF as it is my area of research.

On Mon, 08 Dec 2003 19:58:35 +0100, Sebastian Wiemer wrote:



> 1. The relation between RDF and ticle
> 
> RDF and ticle share the concept of triples - though ticle is more
> abstract than RDF. (E.g.: In RDF the spec differentiates between the
> nature of the subject, the predicate and the object:
> (http://www.w3.org/TR/2003/WD-rdf-concepts-20031010/#dfn-rdf-triple)
> whereas ticle does not.) Ticle says: triples consist of four UIDs: the
> UID for the triple (needed for reification) and the UIDs for subject,
> predicate and object. As a matter of fact there is not even any clear
> binding to the ideas of subject, predicate and object in ticle. Though,
> since a triple is a triple there is no syntactic difference between RDF
> and ticle and it helps some people to understand when calling the first
> triple item "object", the second "predicate" and the third "object".
> 
> 

So, how do you encode relationships that aren't commutative without a
definite binding of subject,predicate,object? You may complain that 'RDF
isn't general enough' but all logic and semantics is about structure. You
can only understand the idea of representation in terms of the structure
of the encoding. Removing all structure is tantamount to removing all
meaning. The developers of RDF spent a long time ensuring that it had just
enough structure to encode an easily processable subset of FOPL.

> Ticle is NOT RDF. Nor does ticle support any out-of-the-box features for
> RDF.
> 
> 

This raises the question of 'what is a feature for RDF?' As far as I'm
concerned RDF itself is just the model that uses triples of URIs.



> a) RDF aims in producing a specification (in XML and graphical) to model
> information -- ticle aims to produce a running system to connect objects
> together (e.g. in plone)
> 
> 

RDF's goals are therefore compatible with information modelling in the
wider world, rather than just objects stored on one server. Why is this
restriction made? What is wrong with RDF as a model? Is there a specific
reason for focusing on a subset of power for greater time expense?

[N.b. XML is only one serialisation of RDF. Recent research by Tim
Berners-Lee has produced the Notation3 and NTriples serialisations for
human readability.]

> b) RDF comes with a predefined set of types and metadata -- ticles
> metadata concept (though a work in progress) is based on the same
> triples that are used to model the content. Thus enabling to change the
> metadata structure in a running system. (See my ideas on the constraint
> manager...)
> 
> 

I'm confused here. What 'standard types' are you talking about? RDF says
very little about anything at all. RDF Schema (an RDF ontology) includes predicates to
describe ontology in RDF, and this is extended by OWL but RDF itself has
no standard types. It is open and extensible. Standard metadata makes no
sense to me either.

> c) RDF is designed to be embedded in XML documents. Ticle is not.
> 

Wrong, RDF/XML is designed to be embedded in XML. RDF is just a labelled
directed graph. XML is actually a very poor medium for this.

> d) RDF uses URIs for referencing - ticle uses referential integral UIDs
> (as a consequence, URIs are accessible directly throug e.g. HTTP whereas
> UIDs must be resolved by ticle.
> 

This shows some great confusion as to what a URI is. A URI is NOT a URL.
All a URI is, is a globally unique way of addressing anything on the
planet that has a unique means of addressing. This includes books (via
ISBNs), loaves of bread (via UPC), telephones (by their number) and much
else besides. This are a globally stable means of doing this too. What one
person labels a book won't change when another person looks at the triple.
This allows easy sharing of graphs and true placeless content. By
contrast, GUIDs by their nature, have a risk of clashing. This may cause
some problems when sharing relations between zope installations and other
information systems (a key requirement for many information systems
buyers.)


> 
> 2. XTM/ISO TopicMaps and ticle (and RDF)
> 
> TopicMaps (in each flavour) are used to model semantics like RDF. The
> big difference is, that RDF looks upon the world thinking: "Everything
> is a resource." Wheras XTM looks upon the world thinking: "Everything is
> a topic." Ticle on the other hand thinks: "Everything is a triple."
> 

No, RDF doesn't claim 'everything is a resource'. It models the world as a
directed labelled graph. The labels are URIs (or in the case of object,
can be a literal.) This is the minimum structure needed to attach some
decent meaning.


> * You have to fully understand what you want to model. Sounds obvious,
> but
>   seems to be one of the big pitfalls. You must understand that there is
>   more than one view of the world. In fact, the idea of one world is
>   absurd! There are many worlds - accept it.
>

RDF already has standard mechanisms for negotiating amongst ontology by
using OWL and RDF Schema inferencing.

> * You must understand the nature of semantics. Labels do not have
>   semantics. Just because you name a topic or resource "table" it does
>   not carry any semantics and it certainly has nothing to do with what
>   we know a table is unless you provide relations and interpretations.
> 

Uh... semantics is JUST labelling and arcs. How the label is interpreted
is often called pragmatics (I generally don't brook pragmatics as it is
too often used as an excuse for intentionalism. Semantics is just a data
structure that can be worked upon by simple algorithms.)


> * You must have a concept of equality to make unification
>   possible. Unification is one of the most important tasks to handle.
>   This is why uniqueness is so important to ticle.
> 
>

Graph unification needs the concept of bottom and complete partial orders
(thus subsumption) more than equality. And the uniqueness requires both
graphs to be defined in the same universe, which GUIDs do not allow.
 

For the information of the group, I'm a semanticist with experience with
RDF, first-order logic, type theory, programming language design,
formal semantics (natural, operational, denotational), RDF, some category
theory (although not much) and natural language semantics (various
models) and general linguistics.

-- 
Joe Geldart
Co-founder, Netalley Networks LLP
http://www.netalleynetworks.com/




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