RE: adding hypermedia to spatial data best practices

Don’t get me wrong – precise link semantics is important. That’s why I prefer time:hasTRS and geom:hasCRS to dct:conformsTo (the latter was suggested on a dcat list in the last week).

Maybe it’s the people I’ve been meeting recently, but I’m finding it still necessary to establish the more basic principles (fine-grained well-managed URIs, hypertext). Mention of RDF and semantic web technologies too esoteric for most web developers, who only know JSON. Depending on the audience, a softly-softly approach is essential, so we must calibrate our discourse overall so we don’t overwhelm them until they are ready. We should practice amongst ourselves, and not gratuitously talk semantics until it is specifically required.

I’m basically supporting Erik’s position – let’s make sure hypertext is on the table first.

Simon

From: Rob Atkinson [mailto:rob@metalinkage.com.au]
Sent: Thursday, 30 July 2015 1:38 PM
To: Kerry Taylor <Kerry.Taylor@acm.org>; Rob Atkinson <rob@metalinkage.com.au>
Cc: Cox, Simon (L&W, Highett) <Simon.Cox@csiro.au>; dret@berkeley.edu; jeremy.tandy@gmail.com; public-sdw-comments@w3.org; eparsons@google.com
Subject: Re: adding hypermedia to spatial data best practices

Do agree - i will submit a Use Case from the Hydrology domain where the link semantics are critical, and not supported by an existing vocabulary.

my thinking is that best practices relate to the use of RDF because we can have flexibility, and make things explicit, but then we need to choose one or all of:
1) strong but generalised semantics - for example spatial relationships
2) strong and domain-specific semantics required to process data in the context of the domain - for example a relationship between a building and a property, or between a hydrological catchment and an upstream catchment
3) weak semantics (where human mediation is probably required - but i suppose deeper discovery of resources could be envisioned)

hopefully a best practice can discuss the pros and cons of each of these, provide examples and importantly shed some light on the practicalities of governance of such vocabularies.  If we can indeed  fit this neatly into the existing 5-star system it should provide a greater sense of how and why "linked data" applies to geospatial information, and we can then perhaps look at the specific case of hypermedia in this context - is it a weak semantics for the link - or is it in fact supposed to support some automated traversal, and if so what is required to do so.

Rob



On Thu, 30 Jul 2015 at 12:55 Kerry Taylor <Kerry.Taylor@acm.org<mailto:Kerry.Taylor@acm.org>> wrote:
All,
In linked data, the meaning of links is always explicit and discoverable-- that is the fundamental reason for the use of formal vocabularies. This also applies to owl:sameAs and rdf:seeAlso, although quite purposefully, rdfs:seeAlso has rather weak semantics. On the other hand, owl:sameAs has very tight semantics, but is very commonly used in a way that violates those semantics. I doubt we can do much about the latter in the broader linked data world, unfortunately.

What we *can* do in this group is to advise on using linking  vocabulary that is well-defined and, if we cannot find such vocabulary already,  to create and define whatever is missing in the spatial space( did I really write that?).   I did not see much in our use cases that suggests new vocabulary is needed, except perhaps in the area of informal spatial relations, where there is no geometry and maybe even very fuzzy location.  I hope that our best practice advice will serve to reduce confusion and encourage publishers to respect the intended semantics of the vocabulary we advise.

I admit to confusion about what 'hyperlinks' and related 'hypermedia' means in this discussion. Is it about links between remote resources only?  Or about links within "media" like video, interactive maps etc ( stuff that is not text or data).? In any case linked data is all about typed links , ie links with meaning, whether internal or remote.
The fifth star does not change the meaning of the links at all,  it only asks publishers to explicitly include some links to remote resources

-Kerry


On 29 Jul 2015, at 3:38 pm, Rob Atkinson <rob@metalinkage.com.au<mailto:rob@metalinkage.com.au>> wrote:
Personally, I think the relationship between "data" and "hyperlinking" needs some greater care.  In a self-contained database, relationships are a first-class concern - however there is a prevalence in the linked data world of using ad-hoc approaches to generating hyperlinks - for example using owl:sameAs to link to an interactive mapping application via geographical coordinates. using very general link semantics "rdf:seeAlso" for links to related data is another common pattern. The lack of a demonstrably good practice is fairly hard to reconcile with any potential to be able to use such links in any automated fashion, so the development of best practice discussion and exemplar resources is an important step to take. fortunately, the Linked Data web is still tiny compared to the problem space, so there is not a huge amount invested in sub-optimal approaches.

I think a "star" that matters is missing - which is to make the meaning of hyperlinks explicit and discoverable - this is far more useful than putting the data into RDF per se, but one could argue thats the underlying intent of using RDF, in that such links have URIs for link predicates - and there is an implication regarding what those URIs should resolve to.  Maybe there is some good practice out there somewhere of how to hyperlink without losing information or adding more noise to the system we could point to - but I haven't seen one in the geospatial domain.

Rob Atkinson


On Wed, 29 Jul 2015 at 11:11 <Simon.Cox@csiro.au<mailto:Simon.Cox@csiro.au>> wrote:
Hmm. That's interesting that you mention the coupling of 'specific model' with 'linked data'. We must be careful about bringing the 5th-star into play too soon. Linked data relies first on (i) stable, resolvable URIs, (ii) open formats, and (iii) hyperlinks, so let's make sure that message gets across first and is not buried in premature focus on semantics.

-----Original Message-----
From: Erik Wilde [mailto:dret@berkeley.edu<mailto:dret@berkeley.edu>]
Sent: Wednesday, 29 July 2015 9:53 AM
To: Jeremy Tandy; public-sdw-comments@w3.org<mailto:public-sdw-comments@w3.org>
Cc: Ed Parsons
Subject: Re: adding hypermedia to spatial data best practices

hello jeremy.

On 2015-07-27 02:44, Jeremy Tandy wrote:
> As one of the editors for the Best Practice doc, I will read through
> the two resources you cite in the hope that there will be less for me
> to write :-) ... seriously though, I will review and match your work
> against our formative requirements. Holiday season is upon us so rate
> of progress might be a little slow ...

no worries. and seriously from my side, i'd love to get feedback and even requests for more detailed content for both resources. i see a lo0t on confusion in the spectrum between linked data (which mandates a specific model that not everybody necessarily wants to use) and no guidance in which case the hypermedia aspect (imho the biggest value proposition of the web by far, when combined with REST's uniform interface constraint) often gets forgotten. thus my attempt to talk about "web data" that focuses on what makes the web valuable, without prescribing a specific path to realize that value.

thanks and cheers,

dret.

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