RE: many-to-many

> -----Original Message-----
> From: Ronan Klyne [mailto:ronan.klyne@xxxxxxxxxxx]
> Sent: Monday, January 29, 2007 5:04 AM
> To: xsl-list@xxxxxxxxxxxxxxxxxxxxxx
> Subject: Re:  many-to-many
>
>
> Brown, William S wrote:
> > Esteemed experts,
> > There are a number of examples out there on the net of
> modelling 'many-to-many' relationship in XML.
> > A recent one is
> >
> http://en.wikibooks.org/wiki/XML:_Managing_Data_Exchange/The_m
> any-to-many_relationship
> > and it is helpful, as far is it goes.
> > However, Kevin Williams points out in
> > http://www-128.ibm.com/developerworks/xml/library/x-xdm2m.html
> > that the usual understanding of the 'many-to-many'
> relationship is that it is a two-way street.
> >
> > That is, to use an example from the first document, I can
> structure data about movies and actors such that each actor's
> info is represented only once in the XML but pulled out
> repeatedly as I generate a list of movies and the many actors
> that appeared in each; same actors appear in multiple movies.
> > Or, to use the classic example, I can represent details for
> each part only once, but re-use it as I generate invoices,
> each of which contains many of the same parts.
> > Each of the above articles suggests an ID/IDREF approach
> for doing this.
> > However, Williams notes that in relational databases it is
> simple to run the query in reverse, i.e., list the movies
> that each actor has appeared in, or list the invoices on
> which each part appears. Since the ID/IDREF is treated as
> unidirectional, he suggests a double IDREF structure - paired
> pointers pointing in opposite directions.
> > Which brings me to my question -
> > has anyone seen any sample xml/xsl that actually
> demonstrated running the query in forward and reverse.
> Everything I've seen uses ID/IDREF and xsl:key in one
> direction and calls that a 'many-to-many' structure. But I'm
> not clever enough to navigate back upstream (William implies
> it can't be done) or to implement the XSL for the dual ID/IDREF.
> > The first (wiki) article contains sample xml and xsl for
> anyone who wants to investigate the issue.
> > I hope you find this diverting (or at least can show me how
> to do it LOL).
> >
> > Best,
> >
> > William S. Brown              wsbrown@xxxxxxx
> > Systems Engineering and Safety Analysis Group
> > Brookhaven National Laboratory
> > Building 130                 TEL 631 344 7230
> > Upton, NY 11973-5000         FAX 631 344 4900
> >
> >
>
> Hi William,
>
> I read the many-to-many problem as two one-to-many problems,
> one in each
> direction, for which keys are a good solution.
> As far as I know, it is not possible to use a key in reverse, so two
> keys must be used; one for each direction.
>
> I include an example involving parts and invoices. Is this the kind of
> thing you had in mind?
>
> 	# r
>
> ----- Input data:
> <doc>
>   <invoices>
>     <invoice id="i1">
>       <part id="1"/>
>       <part id="2"/>
>     </invoice>
>     <invoice id="i2">
>       <part id="5"/>
>       <part id="2"/>
>     </invoice>
>     <invoice id="i3">
>       <part id="5"/>
>       <part id="3"/>
>     </invoice>
>     <invoice id="i4">
>       <part id="5"/>
>       <part id="2"/>
>     </invoice>
>     <invoice id="i5">
>       <part id="3"/>
>       <part id="4"/>
>     </invoice>
>   </invoices>
>   <parts>
>     <part name="part1" id="1"/>
>     <part name="part2" id="2"/>
>     <part name="part3" id="3"/>
>     <part name="part4" id="4"/>
>   </parts>
> </doc>
>
> ----- Stylesheet:
> <?xml version="1.0" encoding="ISO-8859-1"?>
> <xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
> version="1.0">
> <xsl:output method="html" indent="no" encoding="ISO-8859-1"/>
>
> <xsl:key name="p-i" match="/doc/invoices/invoice" use="part/@id"/>
> <xsl:key name="i-p" match="/doc/invoices/invoice/part" use="../@id"/>
>
> <xsl:template match="invoice">
>   <h3>invoice <xsl:value-of select="@id"/> contains:</h3>
>   <xsl:for-each select="key('i-p', @id)">
>     part <xsl:value-of select="@id"/>
>   </xsl:for-each>
> </xsl:template>
>
> <xsl:template match="part">
>   <h3>part <xsl:value-of select="@id"/> was part of invoices:</h3>
>
>   <xsl:for-each select="key('p-i', @id)">
>     <xsl:value-of select="@id"/>
>   </xsl:for-each>
> </xsl:template>
>
> <xsl:template match="doc">
>   <h2>invoice to parts</h2>
>   <xsl:apply-templates select="invoices/*"/>
>   <h2>part to invoices</h2>
>   <xsl:apply-templates select="parts/*"/>
> </xsl:template>
>
> </xsl:stylesheet>
> ----- End.
>
>
> --
> Ronan Klyne
> Business Collaborator Developer
> Tel: +44 (0)870 163 2555
> ronan.klyne@xxxxxxxxxxx
> www.groupbc.com