- From: Eric Prud'hommeaux <eric@w3.org>
- Date: Wed, 25 Aug 2010 09:33:14 -0400
- To: Michael Hausenblas <michael.hausenblas@deri.org>
- Cc: Richard Cyganiak <richard@cyganiak.de>, RDB2RDF WG <public-rdb2rdf-wg@w3.org>
* Michael Hausenblas <michael.hausenblas@deri.org> [2010-08-25 13:52+0100] > > > I propose to proceed based on the concepts of Souri's approach, but > > with an RDF serialization instead of XML as the surface syntax. > > +1 given the community of use, I also see RDF as more practical than XML. > Cheers, > Michael > > -- > Dr. Michael Hausenblas > LiDRC - Linked Data Research Centre > DERI - Digital Enterprise Research Institute > NUIG - National University of Ireland, Galway > Ireland, Europe > Tel. +353 91 495730 > http://linkeddata.deri.ie/ > http://sw-app.org/about.html > > > > > From: Richard Cyganiak <richard@cyganiak.de> > > Date: Wed, 25 Aug 2010 12:42:13 +0100 > > To: RDB2RDF WG <public-rdb2rdf-wg@w3.org> > > Subject: The syntax issue > > Resent-From: RDB2RDF WG <public-rdb2rdf-wg@w3.org> > > Resent-Date: Wed, 25 Aug 2010 11:42:50 +0000 > > > > Harry correctly urges us to press forward with turning the SQL-Based > > Approach into a FPWD. > > > > There is one major obstacle though that needs to be tackled before > > work on a FPWD can be started: the question what syntax the language > > should use. > > > > Ashok has stated that we should talk about syntax ³later², but this > > discussion has to happen before serious work on an official draft > > starts. Once a draft is out, the public will assume that the syntax > > used in the draft is the official and canonical syntax for the > > language, and it is key to send the right signal there. > > > > Which means, the discussion has to happen now. > > > > > > I can understand Souri's decision to base his initial work on XML. But > > I believe that XML is not the best choice of syntax for R2RML. I > > instead propose that R2RML mappings should themselves be RDF graphs, > > with Turtle or RDF/XML as the default syntax for writing R2RML files. > > > > Here is why. > > > > > > 1. CHARTER REQUIREMENTS > > > > The RDB2RDF charter states: ³The mapping language SHOULD have a human- > > readable syntax as well as XML and RDF representations of the syntax > > for purposes of discovery and machine generation.² [1] Using RDF kills > > three birds with one stone: It ticks the RDF box, it ticks the ³human- > > readable syntax² box (Turtle), and it ticks the XML box (RDF/XML). > > > > > > 2. PREFIX HANDLING > > > > The language needs to refer to RDF vocabulary terms, which are > > identified by URIs, and are conventionally represented as QNames or > > CURIEs (that is, http://xmlns.com/foaf/0.1/Person is represented as > > foaf:Person). This means that the language needs features for > > establishing prefix mappings (associate "foaf" with > > "http://xmlns.com/foaf/0.1/ > > "). This is a source of pain in XML-based languages (cf. ongoing > > tensions over RDFa vs HTML5, and RIF's XML syntax). Using a language > > that has a built-in mechanism for establishing prefix mappings and > > expanding QNames/CURIEs would avoid this problem. > > > > > > 3. EXTENSIBILITY > > > > RDF gives us various ways of annotating mappings (e.g., providing > > additional documentation, versioning-related annotations, cross-links > > to other software artifacts etc) for free. For example, I could attack > > rdfs:comment, dc:modified, dc:creator and similar properties to any > > part of a mapping. It also provides a clear syntactical framework for > > vendor-specific extensions. > > > > > > 4. COMMUNITY EXPECTATIONS > > > > R2RML is a language for mapping databases to RDF. Hence, it bridges a > > world that speaks SQL to a world that speaks the RDF technology stack > > (RDF, SPARQL, RIF etc). Hence, arguments can be made for basing R2RML > > syntax on RDF (like in D2RQ or SquirrelRDF), or on SQL (like Virtuoso > > RDF Views), or on SPARQL (like Eric's approach), or on RIF. Basing > > R2RML on XML drags an unrelated third technology stack into the mix. > > > > > > 5. SUITABILITY OF XML FOR CONFIGURATION > > > > XML is a good syntax for text markup (cf. XHTML, DocBook, TEI). It > > works ok for transmitting structured data (cf. SOAP, Atom) albeit > > facing increasing competition from JSON. But I think it is now evident > > that using XML for configuration files that are edited and read > > directly by users is not a good idea. The most obvious drawback in > > this context is that you have to type everything <twice>...</twice>! > > > > > > > > To show what Souri's approach could look like if rendered in RDF > > (specifically Turtle), I took his example [2] and re-wrote it in > > Turtle [3] syntax. You can find it here: > > > > http://www.w3.org/2001/sw/rdb2rdf/wiki/R2RML_in_Turtle > > > > A raw version of just the file [4] and auto-generated graph view [5] > > are also available. > > > > I propose to proceed based on the concepts of Souri's approach, but > > with an RDF serialization instead of XML as the surface syntax. > > > > Opinions? > > > > Best, > > Richard > > > > > > [1] http://www.w3.org/2009/08/rdb2rdf-charter.html > > [2] > > http://www.w3.org/2001/sw/rdb2rdf/wiki/Example_of_SQL-based_RDB2RDF_Mapping:_R > > evision_1 > > [3] http://www.w3.org/TeamSubmission/turtle/ > > [4] http://github.com/cygri/r2rml/raw/master/examples/emp-dept.ttl > > [5] http://bit.ly/asIik4 > > -- -ericP
Received on Wednesday, 25 August 2010 13:33:53 UTC