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Re: Lee's feature proposal

From: Ivan Herman <ivan@w3.org>
Date: Fri, 01 May 2009 13:16:34 +0200
Message-ID: <49FADA12.3050404@w3.org>
To: Lee Feigenbaum <lee@thefigtrees.net>
CC: SPARQL Working Group <public-rdf-dawg@w3.org>
Lee,

Maybe it was not clear from my earlier response, which started a small
thread on OWL: I am fairly happy with your proposal. My (optimistic)
feeling is that, acually, we can handle both SPARQL/OWL and property
paths as part of the 'required' features (and I hope we can...), but it
is fine to leave it as is for now...

Cheers

Ivan

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
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Received on Friday, 1 May 2009 11:16:55 GMT

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