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Comments on datatyping draft

From: Graham Klyne <GK@NineByNine.org>
Date: Fri, 30 Aug 2002 15:49:08 +0100
Message-Id: <>
To: RDF core WG <w3c-rdfcore-wg@w3.org>

Comments based on:

[I've looked very briefly at Patrick's new Part1/Part2 document -- I think 
some of these comments *may* still be relevant, so I'm this posting now, 
without updating it or re-doing the review.]

If I read this in isolation, I'm not sure I'd know what the document was about.

Starting with something like:
This document describes how to reference data type values, such as numbers 
or dates, in an RDF graph. ...
would help.

Section 1:
Seems very heavy on general RDF background -- I'd have thought one short 
paragraph would be enough for that.

1.1 What is Datatyping?

1st para:
Due to RDF's role as a means of interchange between disparate systems, and 
in order to achieve portability and independence of platform it is 
necessary to forgoe any native representation of values or native datatypes 
in RDF itself. This means that
I suggest deleting the above text, leaving:
RDF has no built-in knowledge about particular datatypes such as strings or 
integers, and the lexical representation of a given value, such as the 
number twenty-five "25", has no native interpretation in RDF. RDF is 
datatype neutral in the same manner as it is vocabulary neutral. The 
specific semantics for individual datatypes must reside in the application 
layers above RDF.

1.2 Desiderata for RDF Datatyping

I think this was already noted:  the desiderata seem somewhat out of sync 
with the current goals.

1.5 Comments on the Structure of RDF Literals

I appreciate the text is currently still under review/development, but in a 
final version it might be appropriate to refer to Jeremy's abstract syntax 
for this.

2. RDF Datatypes
Concerning Dan's comments about verbification, I think many of the 
instances of "datatyping" here could be replaced by "datatype" without loss 
of information.  e.g.

Also, I'd suggest simplifying the reference to XML datatypes:

The conceptual framework for RDF datatypes presented in this specification 
uses concepts from the type system defined by XML Schema.  It also can be 
used with any datatype framework which conforms to the characteristics 
defined below.

2.1 rdfs:Datatype

Possible simplification:
An rdfs:Datatype is defined as consisting of

2.3 Typed Literal

A typed literal is a pair where the first element is a URI Reference (or 
implicit systemID) denoting a datatype and the second element is a lexical 
form (literal). Following from the nature of datatypes as defined above, 
this pairing of datatype and lexical form unambiguously identifies a 
specific member of a datatype mapping and hence a specific member of the 
value space of the datatype.
What is an "implicit systemID"?

I think the second sentence is redundant and potentially confusing - I 
suggest removing it.

I think the final paragraph could be pared down to something like:
The means for defining an rdfs:Datatype are not specified here.  It is 
presumed that an agent that needs to interpret a typed literal has 
sufficient knowledge of the datatype used to do so.
In particular, I think the "implicit designation" is incompatible with 
current WG decisions.

3.1 Local Datatyping

I agree that the use of rdf:type here is unfortunate, and likely to 
confuse.  For what I understand to be the current purpose, I'd tend to 
favour using XML schema syntax in a way that is fully compatible with XML 
schema processors, leading to things like:

   <age xsi:type="xsd:integer">25</age>

with appropriate namespace declarations.

3.2 Global Datatyping

I understand the WG has opted to defer this in favour of the datatyped 
literal approach; e.g. per 

Unless I've misunderstood, I think this entire section should be removed.

I would be very wary about trying to incporporate complex XML schema types 
into RDF, as in the vCard example, because that leads to different ways to 
structure the same information.  I believe that would be damaging to 
interoperability between RDF processors.

Section 6
Section number jumps:  shouldn't this be 4?

I'm not reviewing this for now, because I don't think literal subjects are 
part of our current work package.

5. RDF Datatyping Model Theory

I think item (3) is outside the scope of our current goal

6. RDF Schema for Datatyping

I think this is outside the scope of our current goal

6.1.2 CC/PP

I think this example, as stated, is outside the scope of our current goal



Graham Klyne
Received on Friday, 30 August 2002 10:28:30 UTC

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