Geospatial and XQuery?Michael Kay mhk at mhk.me.uk
Tue Oct 4 20:46:33 PDT 2005
Interesting. Did you write up this project? Michael Kay http://www.saxonica.com/ _____ 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 _____ 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 _______________________________________________ http://xquery.com/mailman/listinfo/talk http://xquery.com/mailman/listinfo/talk <http://xquery.com/mailman/listinfo/talk> -------------- next part -------------- An HTML attachment was scrubbed... URL: http://xquery.com/pipermail/talk/attachments/20051004/cbede945/attachment.htm
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