Re: D2RQ and Revelytix semantics

On Mon, Jul 26, 2010 at 6:26 PM, Richard Cyganiak <richard@cyganiak.de>wrote:

> Hi Juan,
>
>
> On 26 Jul 2010, at 21:51, Juan Sequeda wrote:
>
>>
>> https://docs.google.com/document/pub?id=1APTqD2lJLRjwV6gmPKqDRqC3aT8bozHF0udIXndMNWQ
>>
>
>
> The D2RQ bits look good AFAICT.


:)

>
>
>  - Both mapping languages have the semantics established as
>> Database-Instance-and-Schema Mapping [1] (there is a definition of Classes
>> and Properties).
>>
>
> D2RQ is *mostly* database-instance-only. If one uses an auto-generated
> mapping, one can optionally enable the generation of class and property
> definitions for the auto-generated class/property URIs. When the mapping
> author customizes the mapping and replaces the auto-generated URIs with URIs
> from shared vocabularies/ontologies, then these definitions are no longer
> needed.


So this is where I think we need to clarify. AFAICT, ClassMap and
PropertyMap does the following

ClassMap: x -> Class
PropertyMap: y -> Property (where it can be a datatype or object property)

The database-instance-only mapping does not declare a class or property at
all. For example, Triplify outputs triples without defining that something
is a class or something else is a property in the mapping language (SQL).

However, a class and property definition does appear in
the database-instance-and-schema mapping.


>
>
>  There is no way to formally prove this because both
>> languages don't have existing defined semantics (right?)
>>
>
> The semantics of the D2RQ language is defined by the implementation, and
> documented in the manual ;-)
>
> If you talk about *formally* defined semantics, you're right it doesn't
> have it.


Yes, I meant, that the semantics aren't formally defined.

>
>
>  - Revelytix language has different ways of saying the same thing for sake
>> of
>> query optimization ( right?). (I personally believe this is something we
>> should avoid. Language and implementation details should be separate...
>> just
>> look at SQL)
>>
>
> In D2RQ there are a number of instances where one can say the same thing in
> different ways. This is mostly for author convenience -- syntactic sugar.
>

Yes, we definitely need to have syntactic sugar, but I think (IMO) that
different syntaxes shouldn't imply issues in implementation

>
> Best,
> Richard
>
>
>
>
>
>> Looking forward to Alex's presentation tomorrow!
>>
>>
>> [1]
>>
>> http://www.w3.org/2001/sw/rdb2rdf/wiki/Database-Instance-Only_and_Database-Instances-and-Schema_Mapping
>>
>> Juan Sequeda
>> +1-575-SEQ-UEDA
>> www.juansequeda.com
>>
>
>