Re: Direct Mapping

Richard,

Great clarification and +1 on everything.

Given that we are clear that there are two audience, the only thing I'm
saying is that if we are going to write a document on the Direct Mapping,
which one of the audiences is expecting to see a R2RML file... we need to
have a R2RML syntax before we have a Direct Mapping document ready.

Hence my suggestion to put priority on syntax right now.

Juan Sequeda
+1-575-SEQ-UEDA
www.juansequeda.com


On Mon, Sep 6, 2010 at 10:31 PM, Richard Cyganiak <richard@cyganiak.de>wrote:

> Juan,
>
>
> On 6 Sep 2010, at 22:57, Juan Sequeda wrote:
>
>> Let's see if I understand the implied mechanics. Option 1 directly
>>> specifies the RDF graph implied by a database (for any tuple in the
>>> database, you can say exactly what triples are in the direct
>>> graph). Option 2 specifies a mapping language, with certain mapping
>>> semantics, and with a default configuration. The default graph is the
>>> products of applying the mapping semantics for a default configuration
>>> to a database.
>>>
>>>  Option 2 uses R2RML.
>>
>> I see the two options this way
>>
>> Option 1:
>>
>> 1) We (the WG) present the direct mapping rules in order to generate a
>> direct RDF graph from a RDB
>> 2) Database vendors (oracle, db2, etc) implement these mapping rules OR
>> RDB2RDF systems on top of a RDB can read the database dictionary and run
>> these mapping rules
>> 3) You click the button "Generate Direct RDF"
>> 4) Outcomes your RDF
>> 5) Use RDF to RDF tools (sparql constructs, etc) to map to other
>> vocabularies
>>
>> Option 2:
>>
>> 1) We (the WG) present the direct mapping rules in order to generate a
>> direct RDF graph from a RDB
>> 2) Database vendors (oracle, db2, etc) implement these mapping rules OR
>> RDB2RDF systems on top of a RDB can read the database dictionary and run
>> these mapping rules
>> 3) You click the button "Generate Direct RDF"
>> 4) Outcomes your RDF
>> 5) Out comes the R2RML mapping file that generated the Direct RDF Graph
>> 6) A user can modify the R2RML mapping file in order to change
>> vocabularies,
>> etc
>>
>
> I think it would be helpful if you kept stronger awareness of the
> difference between *implementation* and *specification*.
>
> No matter wether our specification describes the direct mapping as a
> mapping to a “direct RDF graph” or to a “direct R2RML file”, vendors are
> free to, and able to, implement either of the two options above. In fact,
> the D2RQ system implements both of the approaches you describe above --
> users can instruct it to dump the direct graph, or they can instruct it to
> create a D2RQ mapping file that can then be customized in order to dump a
> customized graph.
>
>
>  So.. if we agree on this.. we are practically then talking about the same
>> thing. Only difference is that in Option 2 we are outputing the direct
>> mapping also in R2RML. Otherwise.. why would we need R2RML??????
>>
>
> Remember that some people in the WG want what we sometimes call the
> “RDF-based approach”. They want to specify RDB2RDF mappings using, say, RIF
> rules against the direct graph.
>
> So there are at least TWO DISTINCT AUDIENCES for the direct mapping spec:
>
> 1. RDB2RDF vendors who implement R2RML engines and want to equip their
> systems with functionality similar to D2R's "generate-mapping" script, which
> generates a simple canonical R2RML file for a given database, with the
> intent of allowing further customization of the R2RML file by the user.
>
> 2. RDB2RDF vendors who implement RIF-based engines (or engines based on any
> other RDF-to-RDF transformation language). Users of these engines will write
> RIF rules that transform the direct graph into a custom graph. Users and
> vendors of these systems don't need the R2RML language.
>
> Eric's argument (which I find compelling) is this: People in the second
> category are much better served by a specification that describes the shape
> of the direct graph. That they are poorly served by a specification that
> describes the shape of a direct R2RML file, which then under the semantics
> of the R2RML language implies the shape of the direct graph.
>
> (Possibly there is a third audience, vendors of engines that *only* provide
> access to the direct graph without offering the possibility of
> customization. They don't need R2RML either, they just need a spec that
> describes the shape of the direct graph given a DB.)
>
> I hope this clarifies things.
>
> Best,
> Richard
>
>
>
>
>
>>
>>
>>>  So you think that a direct mapping shouldn't output the R2RML file? I
>>>>
>>> think
>>>
>>>> it should because this file is the basis for people to work on and start
>>>> customizing it.
>>>>
>>>
>>> The RDF rules folks will have everything they need with option 1. They
>>> can write/share rules in RIF, SPIN, n3, ... which transform the
>>> default graph to popular ontologies. Simple implementations will
>>> materialize these graphs, and arguably cooler implementations will
>>> work directly on the relational data, but that's really implementation
>>> detail; all they need is the default graph.
>>>
>>>
>>>  Hence I'm with Eric here.
>>>>>
>>>>>
>>>>> The automatic mapping file that is generated in D2R is equivalent to
>>>>>
>>>> the
>>>
>>>> Direct Mapping (right Richard?).
>>>>>>
>>>>>>
>>>>> Well I'd say the *graph* produced by an auto-generated D2R mapping file
>>>>>
>>>> is
>>>
>>>> equivalent to the direct mapping.
>>>>>
>>>>>
>>>> and I'd call the auto-generated D2R mapping file the Direct Mapping
>>>> file.
>>>>
>>> So
>>>
>>>> D2R does option 2 then.
>>>>
>>>>
>>>>> Best,
>>>>> Richard
>>>>>
>>>>
>>> --
>>> -ericP
>>>
>>>
>