[OSGeo-Standards] link relations for features

Peter Baumann p.baumann at jacobs-university.de
Thu Jul 11 15:10:45 PDT 2013

On 07/11/2013 09:17 PM, Rushforth, Peter wrote:
>> I
>> don't mind being at the code level for features, because I
>> think we're ready for that. I just thought the coverages
>> discussion still needs to be on a conceptual level.
> Well I was looking at the wiki page regarding wcs 2.0 that Peter
> pointed to earlier, and I could see a number of ways to look
> at that from a REST perspective that aren't too far afield from
> the discussion of features.  Certainly nothing on that page
> currently qualifies the proposed service as RESTful, IMHO.

hm, according to our discussion thread I see nothing that would disqualify :)
Please let me know the exact definition part which you consider violated, and 
where I can look up why it's violated. This helps us in improving standards.

>> I agree with everything you write below, but I don't think
>> "east" is a useful relation. Half the world is east of any
>> given feature, right?
> If you don't have such a relation, how does the client know how
> to pan?  (Hint: you can't tell me what the URI looks like).

because every pixel has a well-defined topological neighborhood (on raster 
level) or geographic relation (on geo semantic level).

>> I like topological relationships:
>> "within", "adjacent", "crosses", etc., but I think we need
>> more than those, but we also need to avoid the slippery slope
>> of moving into the semantic linked data arena.
> The slippery slope to the Fetid Swamps of Unaddressable Names....

nope, not on grids: mathematically extremely well defined.

>> Here are some
>> other thoughts:
>> - I don't see how a "next" relation helps with geodata
> That's easy.  If a FeatureCollection has 1,000,000
> features in it, do you want to try to parse the whole thing in
> one request/response? OK, how about another zero?  Maybe you do,
> but you shouldn't *have to*.  That is what gives GML a bad name,
> IMHO.  Sorry Ron.

well in the world of image services this is day2day practice since decades:
- give me 1 megapixel (1000x1000)
- give me the NDVI of this
- give me the max/min of that megapixel

so, yes, I want that, and even more: "scan 1,000,000 images, give me the ones 
with less than 30% cloud".
It's the server's business to do this efficiently for me.

>> - I kind of like "near", but don't see how to define it consistently
> It's a good one, I agree.  It should be useful in some situations,
> perhaps a radius search, or equal walking distance search
> etc.

...and many more, in standard remote sensing practice, meteo, aviation, ...you 
name it.

>> - I like the idea of using a standard way of gridding up the
>> world so that our feature collections can be all features in
>> the grid cell, and you can use a "next" relation within the
>> grid cell. The grid gives us a standard way of linking across
>> data sets also.
> The "world" is also a resource.  Maybe it is *the* resource in geo,
> and representations of it contain links to sub-resources, all with
> geospatial (among perhaps other) representations available.

not sure this level of abstraction is leading immediately to user-oriented 
implementations :)


> A grid cell in a standard tile pyramid can then be a sub-representation
> of the world.  It can have a represnetation as image/png or application/road+xml,
> or for the kook kids among us, application/road+json etc.
>> On Jul 11, at 2:15 PM, "Rushforth, Peter"
>> <Peter.Rushforth at NRCan-RNCan.gc.ca> wrote:
>>>> I think Peter Rushforth is saying don't worry about it -- let each
>>>> service implementer design their own link structure.
>>> I agree that it needs to be *possible* to retrieve what is referred
>>> to, but I can imagine that how that retrieval is effected will be
>>> different on different servers and server data structures, and the
>>> 'how' will be reflected in the URL structure.  So spelling out a
>>> standard formula for that structure constrains clients to work with
>>> that instead of working with the representation (format).
>> That is the
>>> problem with OGC specs relative to Web architecture.
>>>> To
>>>> that I say, maybe so, but show me some good strategies and
>> maybe we
>>>> can design some common best practices from there...
>>> Allan Doyle came up with a zinger way back on geo-web-rest:
>>> <link rel="east" href="..." type="application/coverage+xml"/>
>>> I can think of a couple of ways to implement that @href
>> value.  Maybe
>>> spatial folks say "We don't need to be told what east is,
>> we know that
>>> already", but in so saying, you are reversing the contract, you're
>>> telling the server that it has to respect the URL you've coded to.
>>> Let the server tell the client what the URL to the east is,
>> and all of a sudden you've got REST!
>>> Sorry if this takes it back to the "code" level, but that
>> is where the
>>> action is in hypermedia.  At least it's declarative :-).
>>> Does that make sense?
>>> Cheers,
>>> Peter

Dr. Peter Baumann
  - Professor of Computer Science, Jacobs University Bremen
    mail: p.baumann at jacobs-university.de
    tel: +49-421-200-3178, fax: +49-421-200-493178
  - Executive Director, rasdaman GmbH Bremen (HRB 26793)
    www.rasdaman.com, mail: baumann at rasdaman.com
    tel: 0800-rasdaman, fax: 0800-rasdafax, mobile: +49-173-5837882
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