utypes: a proposal

[Roy Williams]

Paul

Once the utype syntax has been decided, it would be nice if it is 
possible to do what tinyurl does (tinyurl.com), so that a 80-character 
utype, all full of dots and colons and semantic wizardry, can be 
converted to four or five random characters. In this way, utypes could 
be used effectively in GET type service calls, like this:

http://my.ser.vice.org?h4gys=6.0&u58dj=273&w98kd=yes

It seems that all we do with utypes is string compare and lookup. Is 
that true? If so, can we at least have a scheme that keeps the names short?

Roy

Paul Harrison wrote:
>
> On 2008-10 -30, at 20:45, Norman Gray wrote:
>
>>
>> On 2008 Oct 30, at 16:19, Paul Harrison wrote:
>>
>>> one of Norman's earlier suggestions 
>>> http://www.ivoa.net/Documents/latest/utype-uri.html.
>>
>> Just to be clear, what I'm suggesting here is independent of this 
>> earlier one.  I think that some of the advantges of the earlier one 
>> would naturally attach to this proposal, but in particular the extra 
>> explanatory structure is not part of what I proposed here.  The 
>> utype-as-xpath suggestion is purely syntactical.
>>>
>
> I have to admit, I am not really keen on the implication that the 
> UType has anything to do with xml - it should be related to a "purer" 
> representation of the data model, as championed by the Theory IG. 
> Having the XML representation of the data model as the "canonical" 
> representation causes problems because of the design decisions that 
> the vagaries of the XML schema language force on the data model author.
>
> Perhaps the problem is that there is  a notion that there should be 
> some way of "reasoning" about the UType from its form, and I think I 
> agree with Doug that the name might allow a human to make some 
> deductions, but in general I think that a machine will not be able to 
> make any - this is why I like your 
> http://www.ivoa.net/Documents/latest/utype-uri.html proposal as it 
> does allow a way to add back the ability to do some machine reasoning.
>
> To take a concrete example - from the using STC in VOtable document 
> http://www.ivoa.net/Documents/latest/VOTableSTC.html
>
> <FIELD name="RAJ2000" ucd="pos.eq.ra;meta.main" ref="Coo1" 
> ID="RAJ2000" utype="stc:AstroCoords.Position2D.Value2.C1" 
> datatype="float" precision="4" unit="deg" />
> When writing software to read this, what are you going to do with the 
> UType here? You could mechanically decompose it and build an STC 
> document that you then parse, but that would seem a little perverse - 
> more likely you will want to directly parse the values into an 
> internal representation of the STC model, an in which case the most 
> likely implementation will be a direct mapping of the UType as a whole 
> to the internal model. This example also shows that the amount of 
> semantic information that a human can read from the UType is also 
> highly dependent on the data model - in this case the UCD is more 
> semantically precise than the UType (which only says that it is the 
> first coordinate of a 2d position), making the UType somewhat 
> redundant, and the software is already going to know the 
> correspondence between the UCD and the position in the STC data model. 
> This makes me wonder whether UTypes and UCDs are really fulfilling 
> distinct roles.....
>
> Cheers,
>     Paul.
>

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