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Re: R2RML draft - new introduction

From: Souri Das <Souripriya.Das@Oracle.com>
Date: Wed, 13 Oct 2010 10:30:26 -0400
Message-ID: <4CB5C282.8010709@Oracle.com>
To: RDB2RDF WG <public-rdb2rdf-wg@w3.org>
Ashok's question is very important and the answer in our FPWD must be 
absolutely clear.

I like the answer Richard came up with after discussing with Michael.

We may want to consider a rephrasing like the following:
"An RDB2RDF mapping may be used against a relational database only if 
the logical table(s) used in the mapping is (are) valid in that 
relational database."

Also, there is an issue of privileges for actually using an RDB2RDF 
mapping:
"A client connecting to the relational database, EITHER to materialize 
the RDF triples based upon an RDB2RDF mapping, OR to query via SQL query 
obtained via translation of a (end-user submitted) SPARQL query using an 
RDB2RDF mapping, must have sufficient privileges in the relational 
database to compute the logical table(s) specified in the mapping."

Thanks,
- Souri.

ashok malhotra wrote:
>  Hi Richard:
> How about "The input to an R2RML mapping is a Relational database 
> which contains the data as well as the schema."
> All the best, Ashok
>
> On 10/13/2010 4:01 AM, Richard Cyganiak wrote:
>> Ashok,
>>
>> On 12 Oct 2010, at 23:59, ashok malhotra wrote:
>>> One question.  You say:
>>>
>>>> The input to an R2RML mapping is a relational database.
>>>
>>> Is it a relational database or a relational database schema?
>>
>> Good question. I discussed this a bit with Michael this morning.
>>
>> Definition: An RDB schema consists of the table *declarations*, but 
>> it does not include the actual *data* in the tables.
>>
>> Definition: A relational database on the other hand consists of both 
>> an RDB schema, and data that populate the tables.
>>
>> The input to an R2RML mapping has to include the actual data, because 
>> otherwise how could a transformed form of the data be part of the 
>> mapping's output? So the input is indeed a relational database.
>>
>> On the other hand, an R2RML mapping is *specific* to an RDB schema. 
>> That is, it only works with an input database that conforms to a 
>> certain schema (contains certain tables and columns). Let's call that 
>> schema the “input schema” of the mapping. One could then say that the 
>> input to a mapping is any database that conforms to the input schema. 
>> In other word, the domain of an R2RML mapping is the set of all 
>> databases that conform to the mapping's input schema.
>>
>> I think the notion of an input schema is actually really valuable for 
>> writing the spec. For example, it allows us to say things like, “the 
>> SQL query in a TriplesMap MUST be a SELECT query that can be validly 
>> executed over the input schema.”
>>
>> Richard
>
Received on Wednesday, 13 October 2010 14:30:59 UTC

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