page 99 xsl:textGlossary Listing: xsl:text
xsl:value-of select=glentry[1]term xsl:text - xsl:text
xsl:value-of select=glentry[last]term title
head body
h1 xsl:textGlossary Listing: xsl:text
xsl:value-of select=glentry[1]term xsl:text - xsl:text
xsl:value-of select=glentry[last]term h1
xsl:apply-templates select=glentry body
html xsl:template
xsl:template match=glentry p
b a name={termid}
xsl:value-of select=term xsl:text: xsl:text
b xsl:apply-templates select=defn
p xsl:template
xsl:template match=defn xsl:apply-templates
select=|comment|processing-instruction|text xsl:template
xsl:template match=xref a href={refid}
xsl:choose xsl:when test=keyterm-ids, refid[1]xreftext
xsl:value-of select=keyterm-ids, refid[1]xreftext xsl:when
xsl:otherwise xsl:value-of select=keyterm-ids, refid[1]
xsl:otherwise xsl:choose
a xsl:template
xsl:template match=seealso b
xsl:textSee also: xsl:text b
xsl:for-each select=java:org.apache.xalan.lib.Extensions.tokenizerefids
a href={keyterm-ids, .id} xsl:choose
xsl:when test=keyterm-ids, .xreftext xsl:value-of select=keyterm-ids, .xreftext
xsl:when xsl:otherwise
xsl:value-of select=keyterm-ids, . xsl:otherwise
xsl:choose a
xsl:if test=notposition=last xsl:text, xsl:text
xsl:if xsl:for-each
xsl:text.xsl:text xsl:template
xsl:stylesheet
page 100
In this case, the
tokenize
function defined in the Java class
org.apache.xalan.lib. Extensions
takes a string as input, then converts the string into a node-set in which each token in the original string becomes a node.
Be aware that using extension functions limits the portability of your stylesheets. The extension function here does what we want, but we couldnt use this extension function with
Saxon, XT, or the XSLT tools from Oracle or Microsoft. They may or may not supply similar functions, and if they do, youll have to modify your stylesheet slightly to use them. If its
important to you that you be able to switch XSLT processors at some point in the future, using extensions will limit your ability to do that.
Hopefully at this point youre convinced of at least one of the following two things:
•
If you have an attribute with a datatype of
IDREFS
, you should use the
id
function to resolve cross-references.
•
The
IDREFS
datatype is pretty limited, so you should avoid using it.
5.2.4 Advantages of the key Function
Now that weve taken the
key
function through its paces, you can see that it has several advantages:
•
The
key
function is defined in a stylesheet. That means I can define any number of relationships between parts of an XML document at any time. If I need to define a
new relationship tomorrow, I dont have to change my XML documents.
•
Any number of
key
functions can be defined for a given element. In our glossary example, we could define
key
functions for the values of the
language
,
topic
, and
acronym
attributes. We could also create
key
functions based on the text of various elements or their children. If we used
ID
s instead of the
key
function, we would be limited to a single index based on the value of the single attribute of the
ID
datatype. To sum up the advantages for this point, an element can have more than one
key
defined against it, and that key doesnt have to be based on an attribute. The key can be based on the elements text, the text of child elements, or other constructs.
•
Any number of elements can match a given value. Taking another look at our glossary example, when we use the
key
function to find all
defn
elements that are written in a particular language, the function returns a node-set that can have any number of
nodes. If we use an
ID
instead, legally there can be only one element that matches a given
ID
value.
•
The value we use to look up elements in the key function isnt constrained to be an XML name. If we use the
ID
datatype, its value cant contain spaces, among other constraints.
5.3 Generating Links in Unstructured Documents
Before we leave the topic of linking, well discuss one more useful technique. So far, all of this chapters examples have been structured nicely. When there was a relationship between
two pieces of information, we had an
id
and
refid
pair to match them. What happens if the XML document youre transforming isnt written that way? Fortunately, we can use the
key
function and a new function,
generate-id
, to create structure where there isnt any.
page 101
5.3.1 An Unstructured XML Document in Need of Links
For our example here, well take out all of the
id
and
refid
attributes that have served us well so far. This may be a contrived example, but it demonstrates how we can use the
key
and
generate-id
functions to generate links between parts of our document. In our new sample document, weve stripped out the references that neatly tied things
together before:
?xml version=1.0 ? DOCTYPE glossary SYSTEM unstructuredglossary.dtd
glossary glentry
termappletterm defnAn application program,
written in the Java programming language, that can be retrieved from a web server and executed by a web browser.
A reference to an applet appears in the markup for a web page, in the same way that a reference to a graphics
file appears; a browser retrieves an applet in the same way that it retrieves a graphics file.
For security reasons, an applets access rights are limited in two ways: the applet cannot access the file system of the
client upon which it is executing, and the applets communication across the network is limited to the server
from which it was downloaded. Contrast with reftermservletrefterm.
defn glentry
glentry termdemilitarized zoneterm
defn In network security, a network that is isolated from, and
serves as a neutral zone between, a trusted network for example, a private intranet and an untrusted network for example, the
Internet. One or more secure gateways usually control access to the DMZ from the trusted or the untrusted network.
defn glentry
glentry termDMZterm
defn See reftermdelimitarized zonerefterm.
defn glentry
glentry termpattern-matching characterterm
defn A special character such as an asterisk or a question mark
? that can be used to represent zero or more characters. Any character or set of characters can replace a pattern-matching
character. defn
glentry glentry
termservletterm defn
An application program, written in the Java programming language, that is executed on a web server. A reference to a servlet
appears in the markup for a web page, in the same way that a reference to a graphics file appears. The web server executes
the servlet and sends the results of the execution if there are any to the web browser. Contrast with reftermappletrefterm.
