- From: Dave Reynolds <dave.e.reynolds@gmail.com>
- Date: Wed, 06 Aug 2014 11:40:29 +0100
- To: public-rdf-shapes@w3.org
Actually, as I noted in my talk at the validation workshop, using SPARQL here was a mixed blessing. On the plus side: 1. We were able to express the checks that we wanted to express. 2. Spec users are able to execute the checks using existing standards-compliant SPARQL engines (mostly, see below). On the minus side: a. Strictly SPARQL wasn't sufficient on its own without some surrounding control machinery. Rules IC-20 and IC-21 are SPARQL templates - you run one query then for each result from that query you instantiate the template, then run all the resulting template instances. b. This is not a human readable way to communicate the constraints. Even the simple cases require thought to interpret, IC-12 and IC-17 are seriously confusing [1]. c. There are some performance issues. The no-duplicates check IC-12 is quadratic (in the number of observations) as expressed in SPARQL and problematic for big data sets. Actual cube validators (at least one the one the GLD WG put up) use custom code to implement this check near linearly, they don't use the SPARQL. Closed world OWL would not be be able to express all of these constraints but that does not rule it of the picture. I wouldn't make "ability to express the Data Cube integrity constraints" a requirement for the outcome of this WG (should it ever happen). As noted in earlier emails, communication of simple constraints (to both human and machine agents) is[2] the primary goal, ability to express arcane constraints is a minor "also ran". Dave [1] At least they confuse me every time I come back to them and I wrote them. [2] "is" in the sense that that seemed to be the outcome of the workshop and accords with experience in Government linked data (e.g. as already expressed by Paul to this group). On 06/08/14 10:27, Richard Cyganiak wrote: > Holger, > > You're right. There wasn't really any alternative, given that currently there is no other W3C-recommended technology that can be used for RDF validation. SPARQL has turned out to be a reasonably good fit for this particular use case. > > The Data Cube experience has left me thinking that a W3C-recommended RDF validation technology should have SPARQL semantics, but that a more compact and idiomatic syntax may be beneficial. > > There was no attempt to write these constraints in closed-world OWL at the time, because that's not a W3C standard, but it would be interesting to see if/how the constraints could be expressed that way. > > Best, > Richard > > >> On 6 Aug 2014, at 08:23, Holger Knublauch <holger@topquadrant.com> wrote: >> >> To those who are critical of using SPARQL as a way of expressing constraints, or as a way of writing specifications, please take a look at >> >> http://www.w3.org/TR/vocab-data-cube/#wf-rules >> >> The Data Cube Vocabulary is a W3C Recommendation that defines its constraints in SPARQL. This is instantly executable. >> >> HTH >> Holger >> >> >
Received on Wednesday, 6 August 2014 10:40:58 UTC