Geospatial and XQuery?

[Michael Kay]

Interesting. Did you write up this project?
 
Michael Kay
http://www.saxonica.com/


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From: Xia Li [mailto:http://xquery.com/mailman/listinfo/talk] 
Sent: 04 October 2005 19:06
To: Michael Kay; http://xquery.com/mailman/listinfo/talk; http://xquery.com/mailman/listinfo/talk
Subject: RE:  Geospatial and XQuery?



I did a bit exploration for extending XQuery to support query on spatial,
spatial temporal and spatial network data types defined in GML (Geographic
Markup Language) last year and an experimental implementation study on a
particular XQuery engine Saxon. I chose to add all operations and functions
defined for the GML types to the system built-in function library. The way
to achieve this in Saxon is to register those functions and bind those
function definitions with the function call in query so that these function
will be processed just like any other system built-in functions. I remember
one advantage of this approach is that once integrating the functions into
the existing architecture we can focus on the implementation of computation
logic of the function itself and do not need to pay attention to do the type
checking for the parameters of the functions which requires the entire
implementation of XQuery sequence type matching. 

 

Another thing I found is that to support spatial network query, one have to
extend XQuery into a high order functional language. 

 

 

Lisa

 

 


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From: http://xquery.com/mailman/listinfo/talk [mailto:http://xquery.com/mailman/listinfo/talk] On Behalf Of
Michael Kay
Sent: Tuesday, October 04, 2005 9:06 AM
To: http://xquery.com/mailman/listinfo/talk; http://xquery.com/mailman/listinfo/talk
Subject: RE:  Geospatial and XQuery?

 

Good point: though I don't think it proves that you need such functions in
the core (standardized) language, only that you need the XQuery engine to be
aware of the functions so that it can optimize them.

 

Michael Kay

http://www.saxonica.com/ 

Without a standard how would an XQuery optimizer know how to deal with a
third-party geospatial function? Execution plans would differ drastically
depending on the cost or absence of spatial indexes, etc.  I recall seeing a
sepecialized XQuery extension standard for text search. It seems like
there's an opprotunity to do the same with geospatial data, especially if it
was written w.r.t common XML geospatial data formats.

 

-Kevin



 

On 10/4/05, Martin Probst <http://xquery.com/mailman/listinfo/talk> wrote: 

Real-To:  Martin Probst <http://xquery.com/mailman/listinfo/talk>
Real-Cc:   http://xquery.com/mailman/listinfo/talk <mailto:http://xquery.com/mailman/listinfo/talk> 

Hi,

> If so, what would the geospatial functions look like in a query?

> Have any of the XQuery or XML database products (commercial or open-
> source) implemented geospatial functions ahead of the spec? If so, 
> what do these look like?

X-Hive/DB is used by Galdos (http://www.galdosinc.com/) in Cartalinea.
They did not need custom functions that much as fast range queries on 
XML attributes, e.g. to find certain specific elements that are within
(in the spatial, not in the XML sense) a set of coordinates.

So basically they needed fast range index lookups on XQuery, XPointer
and XPath queries. 

I don't think there is a need for a standardisation on specific
geospatial functions, especially as you can extend nearly every XQuery
implementation with your own custom functions so you can use these
custom functions as an adaptor-like wrapper around a library in e.g.
Java.

Martin

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