[xquery-talk] Geospatial and XQuery?
xli at galdosinc.com
Tue Oct 4 12:05:46 PDT 2005
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.
From: talk-bounces at xquery.com [mailto:talk-bounces at xquery.com] On Behalf
Of Michael Kay
Sent: Tuesday, October 04, 2005 9:06 AM
To: kfandre at netbox.com; talk at xquery.com
Subject: RE: [xquery-talk] 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.
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.
On 10/4/05, Martin Probst <martin at x-hive.com> wrote:
Real-To: Martin Probst <martin at x-hive.com>
Real-Cc: talk at xquery.com <mailto:talk at xquery.com>
> If so, what would the geospatial functions look like in a
> Have any of the XQuery or XML database products (commercial or
> source) implemented geospatial functions ahead of the spec? If
> what do these look like?
X-Hive/DB is used by Galdos (http://www.galdosinc.com/) in
They did not need custom functions that much as fast range
XML attributes, e.g. to find certain specific elements that are
(in the spatial, not in the XML sense) a set of coordinates.
So basically they needed fast range index lookups on XQuery,
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
implementation with your own custom functions so you can use
custom functions as an adaptor-like wrapper around a library in
talk at xquery.com
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