XSLT 2.0 and XPath 2.0 Programmer's Reference, 4th Edition (172 page)
Read XSLT 2.0 and XPath 2.0 Programmer's Reference, 4th Edition Online
Authors: Michael Kay
You could actually have used a boolean grouping key,
group-adjacent=“boolean (self::SPEAKER)”
, but that would be a little obscure for my taste.
All these examples so far would work equally well using
group-by
rather than
group-adjacent
, because there are no nonadjacent items that would have been put in the same group if you had used
group-by
. But it's still worth using
group-adjacent
, if only because it's likely to be more efficient—the system knows that it doesn't need to do any sorting or hashing, it just has to compare adjacent items.
Example: Handling Repeating Groups of Adjacent Elements
This example is a slightly more difficult variant of the previous example, in which the
Source
If the Shakespeare markup had been done by someone less capable than Jon Bosak, the
I have modified the markup of this (very long) scene from
Timon of Athens
and included it as
timon-scene.xml
.
Output
The required output is the same as in the previous example: that is, a table, in which each row represents one speech, with the names of the speakers in one column and the lines spoken in the other.
Stylesheet
There are various ways of handling such a structure, none of them particularly easy. One approach is to do the grouping bottom-up: First, you put a group of consecutive speakers in a
alternate-groups.xsl
:
group-adjacent=“if (self::SPEAKER) then ‘SPEAKERS’ else ‘LINES’”> group-starting-with=“SPEAKERS”> This does the grouping in two phases. The first phase creates a sequence of alternating elements named If I had presented an example query “find all the speeches in Shakespeare involving two or more speakers and containing two or more lines,” and had presented the solution as This stylesheet produced incorrect output when we tried it with AltovaXML 2008. It works correctly with Saxon and Gestalt. Using group-starting-with Like I could have used this technique for the previous Shakespeare example. In fact, given a scene consisting of alternating sequences of “SPEAKER[not(preceding-sibling::*[1] [self::SPEAKER])]”> Here the pattern that marks out the first element in a new group is that it is a A common use for Example: Handling Flat XHTML Documents This example shows how to create a hierarchy to represent the underlying structure of an XHTML document in which headings and paragraphs are all represented as sibling elements. Source A typical XHTML document looks like this ( Title We need to understand how hierarchies can be flat. Subtitle Let's get to the point. The second paragraph in a section often says very little. But the third gets to the heart of the matter. Subtitle To conclude, we are dealing with a flat hierarchy. This fragment consists of a Output To manipulate this data, you need to transform it into a structure like the one below that reflects the true hierarchy: We need to understand how hierarchies can be flat. Let's get to the point. The second paragraph in a section often says very little. But the third gets to the heart of the matter. To conclude, we are dealing with a flat hierarchy. Stylesheet The group-starting-with=“h2”> group-starting-with=“h3”> I've shown this down to three levels; it should be obvious how it can be extended. When an
group-starting-with
to recognize a group consisting of a
collection (‘shakes.xml’)//SPEECH[SPEAKER[2] and LINES[2]]
, you would probably have found the example rather implausible. But if you want to know how I found the Timon of Athens quote, you have your answer.
group-adjacent
, the
group-starting-with
option selects groups of items that are adjacent in the population, and it therefore tends to be used with document-oriented XML. The difference is that with this option, there doesn't have to be any value that the adjacent nodes have in common: All that you need is a pattern that matches the first node in each group.
group-starting-with
is the implicit hierarchies one sees in XHTML. We will explore this in the next example.
flat.xml
):
element with eight child elements, all at the same level of the tree. Very often, if you want to process this text, you will need to understand the hierarchic structure even though it is not explicit in the markup. For example, you may want to number the last paragraph as1.2.1.
group-starting-with
option is ideal for this purpose, because the
and
elements are easy to match. Here is the code (
unflatten.xsl
):
element is matched, it is processed as part of a group that starts with an
element and then contains a number of
elements interleaved. The template rule first outputs the contents of the
element as a heading and then splits the contents of this group (excluding the first
element, which is of no further interest) into subgroups. The first subgroup will typically start with an ordinary
element. Callmatch = “p”template (for the first group) or thematch = “h2”template (for others). Thematch = “p”template simply copies the group ofmatch = “h2”template starts yet another level of grouping based on the
elements, and so on.Other books
