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Re: R2RML draft - new introduction

From: ashok malhotra <ashok.malhotra@oracle.com>
Date: Wed, 13 Oct 2010 07:12:21 -0700
Message-ID: <4CB5BE45.7090906@oracle.com>
To: Richard Cyganiak <richard@cyganiak.de>
CC: RDB2RDF WG <public-rdb2rdf-wg@w3.org>
  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 14:16:05 UTC

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