Re: R2RML draft - new introduction

On 13 Oct 2010, at 22:49, Juan Sequeda wrote:
> Let R be a relational schema
> Let V be a target vocabulary
>
> R2R(R, V) = RDF graph
>
> Is this correct?

What is “R2R” supposed to be in the formula above?

Richard




>
> Juan Sequeda
> +1-575-SEQ-UEDA
> www.juansequeda.com
>
>
> On Wed, Oct 13, 2010 at 1:50 PM, Souri Das  
> <Souripriya.Das@oracle.com>wrote:
>
>> Not sure if you saw my earlier email ... I am including it here  
>> anyway,
>> just in case:
>> =====================
>>
>> 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.
>> =====================
>>
>>
>> Juan Sequeda wrote:
>>
>> On Wed, Oct 13, 2010 at 1:11 PM, Richard Cyganiak <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 14:17:58 UTC