- From: Boris Villazón Terrazas <bvillazon@fi.upm.es>
- Date: Thu, 14 Oct 2010 03:10:26 +0200
- To: Juan Sequeda <juanfederico@gmail.com>, RDB2RDF WG <public-rdb2rdf-wg@w3.org>
- CC: Souri Das <Souripriya.Das@oracle.com>, Richard Cyganiak <richard@cyganiak.de>, ashok.malhotra@oracle.com
- Message-ID: <4CB65882.7060105@fi.upm.es>
Hi Juan On 13/10/2010 23:49, Juan Sequeda wrote: > I don't think answers my question. > > Just to make sure that I understand what is being proposed, I see as > the following: > > Let R be a relational schema > Let V be a target vocabulary > > R2R(R, V) = RDF graph > > Is this correct? As far as I understand and according to the introduction: R2RML is a language for expressing customized mappings from relational databases to RDF datasets. Again, I took the liberty of creating a preliminary diagram that depicts this definition. You can find it at: http://mccarthy.dia.fi.upm.es/rdb2rdf/R2RML.png IMHO, a R2RML mapping only expresses the mappings from RDB to RDF. A specific R2RML engine takes as input: the R2RML mapping, the RDB connection info, the target RDF dataset (vocabulary?) and generates as output an RDF dataset Or am I wrong? Boris > > Juan Sequeda > +1-575-SEQ-UEDA > www.juansequeda.com <http://www.juansequeda.com> > > > On Wed, Oct 13, 2010 at 1:50 PM, Souri Das <Souripriya.Das@oracle.com > <mailto: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 <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 01:10:56 UTC