[Versa] Issue 1, better literal and datatype support

[Michael Olson]

On Aug 12, 2005, at 9:27 AM, Uche Ogbuji wrote:

> On Fri, 2005-08-12 at 09:08 -0600, Michael Olson wrote:
>>>>
>>>> I had exactly the same suggestion.  So your suggestion a literal
>>>> datatype as a *replacement* for strings and numbers?  If so, I'd
>>>> agree, since that would completely cover all literals (especially if
>>>> we include the capablity to associate xsd - or other - datatypes to
>>>> the underlying model) and would be more inline with RDF Literals.
>>>
>>> I don't know.  I think that would suck in syntactic terms.  In cases
>>> such as
>>>
>>> length($mylist, 1)
>>>
>>> That 1 is more at the Versa layer, and I don't think it should be
>>> changed to
>>>
>>> length($mylist, "1"^^xsd:int)
>>>
>>
>> Why.  We convert plain strings to numbers according to section 3.
>
> Too much typing, for one thing.  Do you really want to be forced to  
> type
> '"1"^^xsd:int' rather than '1' every time?  I don't.  I'm fine with an
> automated cast, but not with typed literals as a replacement for Versa
> primitives (which is what Chime said int he para I responded to).

Oh.  I agree totally.  Besides as I said earlier we cannot guarantee  
that the model understands xsd so we cannot rely on it.

>>>>
>>>> uuu aaa lll (where lll is a plain literal (with or without a  
>>>> language
>>>> tag)
>>>>
>>>> implies
>>>>
>>>>  _:nnn rdf:type rdfs:Literal .
>>>>
>>>> where _:nnn identifies a blank node allocated to lll by rule rule  
>>>> lg.
>>>>
>>>> So, the literals themselves are thought of as resources by the RDF
>>>> model (especially if they are typed)
>>>
>>> Did the latest RDF specs really do that?  That's really bloody messy.
>>> So to what extent do these magic blank nodes confer identity on
>>> (previously identified) literals?
>>
>> You should read the spec.  There is equiality between literals.
>
> Equality has nothing to do with identity.
>

If they are equal then they are identical.

given:
a --> b --> "c"
a --> d --> "c"

you get (with simple entailment only)

_a --> _b --> _c
_a --> _d --> _c

Same if you do and have d-entailment

a --> b --> "c"
a --> d --> "c"^^xsd:string

>
>>>   To what extent does this bloat the
>>> model?
>>>
>>
>> It actually helps in so many ways (having just implemented it).  Both
>> in model size (now a statements table only needs three columns not
>> four),
>
> You mean "column count", not "model size", right?
>

No, and model size.  No identical literals have the same blank node  
they reduce the number of string literals in the model.

>> interfaces, no more addStatement for literals and addStatement
>> for resources, queries, etc.
>
> I don't understand this at all.
>

Probably not an issue in python land, in java land you needed
addStatement(Resource subject, Resource predicate, Resource object)
addStatement(Resource subject,Resource predicate, String object)

Similarly in 4RDF, there is an "object type" parameter in the  
constructor of a statement.  This would go away.

>
>>> BTW, You mentioned language specifiers.  I think we should add those  
>>> as
>>> well, while we're on data types.
>>
>> Yep
>>
>> BTW, can someone fix the reply-to on this list so we don't continually
>> get 2 copies of the message.
>


> No.  I don't intend to turn on reply-to munging.  We don't have it on
> for any of the other lists on lists.fourthought.com because I (and many
> others) think it's bad form.  Even mailman agrees, having munging off  
> as
> a default, but that doesn't matter.  The debate has raged for years,  
> and
> I'm firmly on one side, and I won't administer any list with reply-to
> munging (I barely tolerate being on them).
>

Geez.  The net picks such weird things to piss and moan about......

> I should do a better job of trimming headers (Ctrl-L in Evolution  
> rather
> than Shift-Ctrl-R, BTW), and I shall.
>

If only it was so easy on a Mac.....

Mike

>
> --  
> Uche Ogbuji                               Fourthought, Inc.
> http://uche.ogbuji.net                    http://fourthought.com
> http://copia.ogbuji.net                   http://4Suite.org
> Use CSS to display XML, part 2 -  
> http://www-128.ibm.com/developerworks/edu/x-dw-x-xmlcss2-i.html
> XML Output with 4Suite & Amara -  
> http://www.xml.com/pub/a/2005/04/20/py-xml.html
> Use XSLT to prepare XML for import into OpenOffice Calc -  
> http://www.ibm.com/developerworks/xml/library/x-oocalc/
> Schema standardization for top-down semantic transparency -  
> http://www-128.ibm.com/developerworks/xml/library/x-think31.html
>
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-----------------
Mike Olson                                                Principal  
Consultant
mike.olson at fourthought.com                +1 720 253 4662
Fourthought, Inc.                                       
http://Fourthought.com
PO Box 270590,                                       http://4Suite.org
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