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Re: plural vs singular properties (a proposal)

From: Garret Wilson <garret@globalmentor.com>
Date: Sat, 05 Jan 2008 14:11:39 -0800
Message-ID: <4780009B.9080507@globalmentor.com>
To: Frank Manola <fmanola@acm.org>
CC: SWIG <semantic-web@w3.org>

Frank, thank you *very* much for your clarifications; they help 
immensely. Just a couple more comments below:

Frank Manola wrote:
>
>>
>> 3. The semantics of the relational model when "interpreted in an 
>> obvious way" by Date in his wine example is an interpretation 
>> incompatible with and therefore unsuitable for representing RDF 
>> because it does not allow each predicate to be duplicated in the 
>> relation header.
>
> I don't think it's a matter of the interpretation being incompatible.  
> The relational model simply requires that when you have a situation in 
> which it appears a predicate must be repeated (or a single predicate 
> must have multiple values), you must define a separate relation.

Yes, obviously some RDF subsets can be mapped to the relational model in 
several ways. As relating to my original question, though, I could not 
choose the semantics "interpreted in an obvious way" by Date as a way to 
support general RDF data. In other words, Date's interpretation is 
*only* compatible with storing a *strict subset* of RDF data; there 
exists RDF data that would not fit into this interpretation. This is the 
sense in which I meant that this interpretation (let's call it the 
"obvious" interpretation, using Date's words) is incompatible with RDF 
(the model) as a general interpretation, because it cannot represent 
everything expressible by RDF.

After I wrote my other emails, I came across an interesting note from 
TBL regarding the "obvious" interpretation of the relational model:

"The semantic web data model is very directly connected with the model 
of relational databases. A relational database consists of tables, which 
consists of rows, or records. Each record consists of a set of fields. 
The record is nothing but the content of its fields, just as an RDF node 
is nothing but the connections: the property values. The mapping is very 
direct

    * a record is an RDF node;
    * the field (column) name is RDF propertyType; and
    * the record field (table cell) is a value.

Indeed, one of the main driving forces for the Semantic web, has always 
been the expression, on the Web, of the vast amount of relational 
database information in a way that can be processsed by machines."

Tim Berners-Lee, "Relational Databases on the Semantic Web", 
<http://www.w3.org/DesignIssues/RDB-RDF.html> (1998)

This interpretation seems as obvious to TBL as it does to Date. Perhaps 
the only thing to add here is that TBL is correct in that the "obvious" 
interpretation of the relational model is a good one for getting data 
*out* of a relational database into RDF, but not out of RDF *into* a 
relational database unless you restrict expressibility of the RDF model 
(i.e. only work with a subset of available RDF data).

So back to my original question: does that make me uncomfortable? I 
dunno. Maybe.

Cheers,

Garret
Received on Saturday, 5 January 2008 22:13:22 GMT

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