Re: R2RML draft - new introduction

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. The input to an R2RML mapping is a relational  
database that conforms to the schema. The output is an RDF dataset, as  
defined in SPARQL, that uses predicates and types from the target  

This is for the intro; in the later chapters there is more space to  
spell it out in detail.


> 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 18:12:30 UTC