- From: Jiří Procházka <ojirio@gmail.com>
- Date: Wed, 10 Nov 2010 03:39:05 +0100
- To: public-lod@w3.org
- Message-ID: <4CDA05C9.20708@gmail.com>
Hi, having read all of the past week and still ongoing discussion about HTTP status codes, URIs and most importantly their meaning from Linked Data perspective, I want share my thoughts on this topic. I don't mean to downplay anyone's work but I think the role of URI and HTTP specifications (especially semantics) in Linked Data is overemphasized, which unnecessarily complicates things. I think we can all agree, that the core idea of Linked Data is that information is expressed using unique identifiers (URIs) I can simply use to get useful information about the thing the identifier represents (thus mandated relatively simple, widely supported transfer protocol HTTP). So lets stick with this. Lets just treat URIs as RDF does - as simple names. When we dereference an URI we get back some useful data and that's it. If we want to express, the data fetched are in fact a document, we use the wdrs:isDefinedBy property. The data fetched are just a data and any info about it should be contain in it. Why? Why no Content-Location? There is no reason to require additional complexity, building extra information layers. Publishing the document information in the data itself most probably would be simpler for both the publishing and the consuming party. Treating HTTP as a simple blackbox is what is mostly done in practice anyway. What if someone doesn't publish the document data? Would it mean the URI we dereferenced refers both to the thing described and the description of it? Kind of. What I mean is the consumer side can add additional information to the data about the document (when and how fast it was fetched etc) and if the data doesn't contain info about the document already, it could add it: <uri> wdrs:isDefinedBy [ wdsr:location "uri" ] . # or something like this Non-RDF data should use their equivalents. That is the most important things I had to say - lets keep semantics in the data. I believe it is quite important that the range of wdrs:isDefinedBy is a document class, which should be domain of wdsr:location. I am going to explain why I think so, but beware, at this point I get a bit philosophical :) What is pretty awesome about RDF, which is something Linked Data could learn, is how it dabbled the ontological (used as philosophical term) issues - existence, being and reality. In order to support maximum expressiveness and compatibility with various world-views it says the least about it. Big part of that is dealing with identity - if a caterpillar turns into butterfly, is it still the same thing? Am I still I when I get older and change? RDF doesn't offer any answers to such questions, neither if there are only information resources and other resources. There are just names which identify objects or concepts, which we describe with names and the final description matches some number of objects or concepts we know, while the better the description is, the lower the number is. RDFS classes are used to describe various aspects of objects or concepts, which allow us to express ourselves much less ambiguously, using properties with defined domain and range. On the other hand we can describe those aspects separately if we consider them a separate entity. For example someone can say I am averagely skilled as an English speaker, or that my English skill is mediocre, or that I am one of averagely skilled English speakers. Similarly one could say <book> is long 30000 characters as its content, or that <book> is long 20 characters as its title, or that <book> is long 3000 characters as the description received on dereferencing. It shouldn't matter if I consider a book name as part of it or not, if I use as unambiguously defined properties as possible. However vocabularies with not very well defined terms (consider an example "length" property), which generally mimic natural language properties, are used widely, which is why we should have wdrs:isDefinedBy. The point of this philosophical exercise was to say, that shouldn't be saying "an URI represents one resource" or trying to define what resources are or what existence is, but recognizing the context of the original information when modifying it (especially amending). Best, Jiri Prochazka PS: It might be useful to also have wdrs:isPrimarilyDefinedBy (as rdfs:subPropertyOf wdrs:isDefinedBy).
Received on Wednesday, 10 November 2010 02:39:40 UTC