Subject: Re: How to transform flat structure into hierarchical one? From: "Steve Muench" <smuench@xxxxxxxxxxxxx> Date: Thu, 8 Jun 2000 08:00:33 -0700 |
| Unfortunately, Steve discovered this *after* | Mike Kay's book came out. I have added a special note | to my copy at the bottom of page 560 to help | remind me to use the Muenchian technique | instead whenever I have a grouping problem to solve. Jenny, I bumped into this idea while writing up a section in my forthcoming book on Building Oracle XML Applications for O'Reilly, where I was trying to understand and subsequently explain the cases where using the database to do the data "shaping"/grouping was best and where doing a single query and allowing XSLT to do the grouping was best. The data "shaping" techniques supported in Microsoft ADO and in Oracle using nested CURSOR() expressions end up achieving the result using many individual data cursors and trips across the networks. Depending on the amount of data this might be too much network traffic. The XSLT grouping approach can be better in some scenarios when doing a single query to join a master and a detail table doesn't result in tons of duplicated data. So, given a trivial example like a DEPT and an EMP table... If you want to include just a little information (like Dept Name) from the DEPT table, then it's probably better to join DEPT and EMP and let XSLT "group" the joined data. This is especially true if there are hundreds or thousands of employees. If instead you need 30 columns of information from DEPT and 30 columns of info from EMP, then joining them will produce lots of redundant DEPT info. In that case it's better to let the DB to the data shaping to deliver an XML document that pre-grouped into departments. ______________________________________________________________ Steve Muench, Lead XML Evangelist & Consulting Product Manager Business Components for Java & XSQL Servlet Development Teams Oracle Rep to the W3C XSL Working Group Author "Building Oracle XML Applications", O'Reilly, Oct 2000 XSL-List info and archive: http://www.mulberrytech.com/xsl/xsl-list
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