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Re: R2RML draft - new introduction

From: Richard Cyganiak <richard@cyganiak.de>
Date: Thu, 14 Oct 2010 15:17:37 +0100
Cc: Juan Sequeda <juanfederico@gmail.com>, ashok.malhotra@oracle.com, RDB2RDF WG <public-rdb2rdf-wg@w3.org>
Message-Id: <02E610B4-810D-4107-A2A9-BBAD647B4197@cyganiak.de>
To: Souri Das <Souripriya.Das@oracle.com>
Souri,

On 13 Oct 2010, at 19:50, Souri Das wrote:
> 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."

These should definitely go in, but not in the introduction, but in a  
later chapter.

Richard



>
> Thanks,
> - Souri.
> =====================
>
> Juan Sequeda wrote:
>> On Wed, Oct 13, 2010 at 1:11 PM, Richard Cyganiak <richard@cyganiak.de 
>>  <mailto:richard@cyganiak.de>> wrote:
>>
>>    On 13 Oct 2010, at 15:12, ashok malhotra wrote:
>>
>>        How about "The input to an R2RML mapping is a Relational
>>        database which contains the data as well as the schema."
>>
>>
>>    Well, the input can't be a database with *any* schema; it must be
>>    the same schema that the mapping was written for. I'd like to make
>>    that as clear as possible.
>>
>>    How about this:
>>
>>    “Every R2RML mapping is tailored to a specific database schema and
>>    target vocabulary.
>>
>>
>> target vocabulary or vocabularies
>>
>>    The input to an R2RML mapping is a relational database that
>>    conforms to the schema.
>>
>>
>> so you mean:
>>
>> RDB and Vocabulary --> R2RML Mapping --> RDF
>>
>> or is a R2RML mapping and input self:
>>
>> RDB and Vocabulary and R2RML Mapping --> RDB2RDF System --> RDF
>>
>>
>>    The output is an RDF dataset, as defined in SPARQL, that uses
>>    predicates and types from the target vocabulary.”
>>
>>    This is for the intro; in the later chapters there is more space
>>    to spell it out in detail.
>>
>>    Richard
>>
>>
>>
>>
>>
>>
>>        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 Thursday, 14 October 2010 14:18:11 UTC

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