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Re: Lee's feature proposal

From: Ivan Herman <ivan@w3.org>
Date: Fri, 01 May 2009 09:59:06 +0200
Message-ID: <49FAABCA.9010109@w3.org>
To: Lee Feigenbaum <lee@thefigtrees.net>
CC: SPARQL Working Group <public-rdf-dawg@w3.org>, Bijan Parsia <bparsia@cs.man.ac.uk>
Hey Lee,

I see you have decided to live dangerously:-)

I have a clarification question which is as much to Bijan as to you
(hence adding Bijan explicitly to the cc list) and that is related to
SPARQL/OWL. From a user point of view, there is actually a palette of
semantics that SPARQL users may want to use if they want to get away
from the simple graph semantics. This includes RDFS, RDFS+D Entailement,
OWL also has 'species', because it has two different semantics (direct
and RDF compatible, usually referred to as OWL DL and OWL Full), plus
the profiles worked on by OWL 2, namely QL, EL, and RL. For many RDF
users RDFS (with possibly D-entailement) and OWL RL (maybe OWL QL) may
be the most important target, for example.

It is not clear to me (lack of my technical knowledge!) whether Bijan's
SPARQL/OWL proposal covers both semantics of OWL or not. OWL DL is, in
many respect, a loose sub thing to OWL Full, so it might, but we have to
be very explicit (at charter time, too!). So it would be good to put my
mind at ease:-) How would we handle the others like RDFS?

I presume service descriptions play an important role here.

Thoughts?

Ivan

P.S. The OWL WG has had the experience of finding itself in the eye of
the storm that is sometimes (alas!) raging in the SW community at large.
We have to avoid talking, eg, about OWL DL + SPARQL only if we want to
avoid similar issues for this group...


Lee Feigenbaum wrote:
> Hi everyone,
> 
> I've posted my proposal for what features the Working Group should work
> on on the wiki at:
> http://www.w3.org/2009/sparql/wiki/User:Lee_Feigenbaum#Lee.27s_feature_proposal
> 
> 
> I've copied it in at the end of this note; it contains my reasoning
> behind my suggestions.
> 
> Regarding Rec. track vs. WG Notes. I do _not_ think that we should
> distinguish between these when choosing what features we're going to
> work on at this point, and here's why. (I'm not a process expert, this
> is purely my understanding.)
> 
> 1) A document can be developed quite far before the group needs to
> decide whether it shoudl be Rec. track or not.
> 
> 2) WG Notes are first published as First Public Working Drafts, at which
> point they carry the same IP requirements and exclusion opportunities as
> any document intended for Rec. track - in light of our need to
> re-charter with a specific list of deliverables, then, we should include
> in our decision any material we plan to work on, whether it ends up a
> Note or a Rec. track document.
> 
> 3) I don't think we should view Notes as things to be churned out
> quickly and without much consideration or review. Rather, I think Notes
> are best used for material that may not be core to the language or
> protocol, that may represent a best or common practice (as in the JSON
> results format), or that is a common but difficult-to-implement
> extension such that the group feels that a Note would document
> interoperable semantics without requiring multiple implementations to
> move through the Rec. track.
> 
> Please note that I wrote some of this proposal before some of the more
> recent survey responses. I've taken a look at those responses, which
> don't change the meat of my proposal (I made one small change to a
> prioritization), but note that the exact numbers for some of my
> reasoning (when I refer to the survey results) may no longer be fully
> accurate.
> 
> 
> Lee
> 
> Lee's feature proposal
> 
> The following is a proposal for the features that the SPARQL WG should
> adopt. It is an attempt to reach consensus by balancing previously
> stated goals including
> 
>     * group preference
>     * group energy
>     * implementation experience
>     * utility to developers
>     * utility to end users
>     * extensibility
>     * conservatism
> 
> [edit] Constraints
> 
> On April 28 the group resolved to accept aggregates, subqueries, and
> update as deliverables.
> [edit] Proposal
> [edit] Required Features
> 
>     * Aggregate functions
>     * Subqueries
>     * Update
>     * Project expressions
>     * Service description
> 
> [edit] Time-permitting Features
> 
> (Roughly in this order.)
> 
>     * SPARQL/OWL
>     * Property paths
>     * Function library
>     * Basic federated query
>     * Surface syntax
> 
> [edit] Commentary
> 
> This proposal has 5 mandatory features and 5 time/energy-permitting
> features. This is more than I think is desireable, but I have a hard
> time making the proposal narrower.
> 
> The required features consist of the three features identified early on
> as having the highest level of consensus.
> 
> I've also included as required project expressions, the ability to
> include arbitrary expressions in a SELECT clause. The aggregate feature
> already requires the group to find a way to include values not
> explicitly mentioned in the RDF dataset in a query's results (i.e. the
> computed value of aggregate functions), and it seems confusing and
> unnecessarily limiting to not also allow the same or a similar
> (syntactic) mechanism to be allowed to introduce new scalar values into
> query result sets. In addition, project expressions in conjunction with
> the othe required features enables the same capabilities as various
> other proposed features, including assignment and scalar expressions in
> construct. Project expressions receives significant but not overwhelming
> WG support in our survey, with five organizations ranking it amongst
> their top four features, and no organizations explicitly objecting to
> it. Project expressions is widely implemented in existing SPARQL engines.
> 
> Finally, I suggest that service description be a required deliverable of
> the Working Group. While there are various design pieces to draw on,
> service description carries the challenge of the Working Group doing a
> fair bit of design work. However, I believe that this sort of
> leading-edge-of-the-curve design work is appropriate for the SPARQL WG
> in the case of a feature such as service description that is an
> extensibility point and an enabler for future standardization efforts.
> Service description provides a standard way for extended SPARQL
> implementations to advertise their capabilities, and in doing so
> encourages similar implementations to coalesce around common syntax and
> semantics of extensions. It can be used to advertise entailment regimes,
> extended surface syntax, data set information (including optimization
> hints for federation), supported functions, and much more. Service
> description received moderate WG support in the survey (5 organizations
> including it in their top 10), and no organizations explicitly objected
> to it. With Condorcet, service description is preferred to everything
> except the top 3 features and negation. (See below for more on negation.)
> 
> I've included five time-permitting features in this proposal, ranked
> roughly in the order in which I believe the group should pursue them. I
> acknowledge at the same time that some of these efforts can reasonably
> go on in parallel with either other time-permitting features or in
> parallel with development of required features.
> 
> I believe that SPARQL/OWL is an important deliverable for this WG. The
> SPARQL community sees somewhat of a divide between those using SPARQL
> purely to query RDF graphs, and those using SPARQL in conjunction with
> richer semantics. The original SPARQL effort acknowledged this by
> providing a mechanism to define extensions that would define basic graph
> pattern matching for entailment regimes other than simple entailment.
> This extension mechanism is key to enabling groups other than the SPARQL
> working group (whether formal or informal groups) to define how SPARQL
> queries behave in the presence of other semantic regimes. But the
> extension mechanism has never been formally tested, and it seems to be
> prudent to test it (a) under the auspices of the SPARQL WG, so that the
> results may feed back into the SPARQL BGP extension specification itself
> and (b) in the context of OWL semantics, probably the most popular
> richer entailment regime that currently exists. There are numerous
> implementations that implement SPARQL/OWL already, though likely not in
> an interoperable fashion. And in the personage of Bijan Parsia, the
> SPARQL WG has the expertise and energy necessary to properly specify the
> SPARQL/OWL basic graph pattern matching extension. SPARQL/OWL received
> minimal support in the survey, but seemed to have a somewhat warmer
> reception in the discussion on the April 28 teleconference.
> 
> I believe that property paths is an important deliverable for the WG as
> it enables variable-length path queries for SPARQL developers. It has
> significant support within the WG, and it also enables most cases of the
> accessing RDF lists proposed feature.
> 
> I believe that Surface syntax and Function library represent reasonable
> maintenance tasks for the WG to examine, time-permitting. Accepting
> surface syntax as a time-permitting feature gives the WG an opportunity
> to examine capabilities of the SPARQL language that are particularly
> onerous to use and to consider specialized syntax for these features.
> Accepting function library allows the WG to consider extending the core
> set of functions available when moving between SPARQL implementations to
> include things like basic string or mathematic operations.
> 
> Finally, I believe the WG should deliver a specification for basic
> federated query, time-permitting. Federated query is implemented in a
> variety of forms in several implementations, and the feature received
> significant support in the survey (6 organizations including it amongst
> their top six choices). I believe that looking at a design for basic
> federated query is important for the growing Linked Data community, and
> the time is ripe to standardize on basic federated query as a way to
> encourage implementations to explore more and more sophisticated
> approaches to federated query.
> 
> This proposal leaves out many good features, and I'd be remiss not to
> address several specific ones.
> 
>     * Negation. The survey indicated strong support for providing a
> simpler form of asking negative queries than the current OPTIONAL/!bound
> construct. I've excluded this from my proposal under the hope that the
> design for subqueries may obviate the need for this feature.
>     * Full text. The survey indicated strong support for standardizing
> the syntax and semantics for full text search in SPARQL. While I believe
> that this is one of the top interoperability stumbling blocks for
> SPARQL, the wide-open design space (both for syntax and semantics) of
> the problem worries me.
>     * Parameterized inference. The survey indicated support from a small
> number of organizations for parameterized inference. The discussion
> during the April 28 teleconference made clear to me that some members of
> the WG see a need both to define what it means to query other entailment
> regimes (a la SPARQL/OWL) and also how to go about doing that on a
> query-by-query basis. The latter is what parameterized inference is
> about. I have omitted parameterized inference from my proposal because
> of the lack of existing implementations/designs to draw on, coupled with
> the fact that service descriptions provide an out-of-band way for
> endpoints to indicate the entailment regime or rulesets that they
> service. I recognize that this does not fully address the use case of
> on-demand rulesets, but I believe that this would be better served via a
> SPARQL protocol feature, and I do not see any mature designs yet in this
> space to draw upon. I believe that (1) standardizing on the semantics of
> SPARQL/OWL and (2) the increasing maturity and deployment of RIF, will
> encourage SPARQL implementations to begin to explore this space more and
> make this an appropriate feature for a future round of standardization.
> 
> 

-- 

Ivan Herman, W3C Semantic Web Activity Lead
Home: http://www.w3.org/People/Ivan/
mobile: +31-641044153
PGP Key: http://www.ivan-herman.net/pgpkey.html
FOAF: http://www.ivan-herman.net/foaf.rdf

Received on Friday, 1 May 2009 07:59:23 GMT

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