Subject: Re: [xsl] Intersection of two sets based on a subset of fields? From: "Michael Kay mike@xxxxxxxxxxxx" <xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx> Date: Thu, 21 May 2020 14:45:39 -0000 |
In the language of relational algebra, it's a join, not an intersection. In XSLT, joins are best performed using the key() function. In XSLT 2.0 (or is it 3.0?) you can define a composite key with multiple fields. Michael Kay Saxonica > On 21 May 2020, at 15:17, Roger L Costello costello@xxxxxxxxx <xsl-list-service@xxxxxxxxxxxxxxxxxxxxxx> wrote: > > Hi Folks, > > I have a set of Book instances. I call this Set #1. Here are two instances: > > <Book> > <Title>ABC</Title> > <Author>John Doe</Author> > <Country>USA</Country> > <Binding>hardcover</Binding> > </Book> > > <Book> > <Title>XYZ</Title> > <Author>Mary Sue</Author> > <Country>CAN</Country> > <Binding>hardcover</Binding> > </Book> > > I have a set of Music instances. I call this Set #2. Here is one instance: > > <Music> > <Genre>Classical</Genre> > <Author>John Doe</Author> > <Country>USA</Country> > <Cost>9.95</Cost> > </Music> > > Query: Find the subset of Set #1 that intersects with Set #2 at the <Author> and <Country> elements. > > If Set #1 consists of the two instances shown above and Set #2 consists of the one instance shown above, then the result of the query is the following: > > <Book> > <Title>ABC</Title> > <Author>John Doe</Author> > <Country>USA</Country> > <Binding>hardcover</Binding> > </Book> > > That Book instance has an <Author> and <Country> that intersects with the <Author> and <Country> in the Music instance. > > I view this as an intersection problem. However, it is an intersection at specific fields (the Author and Country fields). Do you view it as an intersection problem? > > If it is viewed as an intersection problem, then is there a nice XPath expression that does intersection-at-specific-fields? > > If it is better viewed not as an intersection problem, then how is it better viewed? is there a nice XPath expression for that view? > > /Roger
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