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| <TABLE border="0" cellpadding="0" cellspacing="0" width="494"><TR><TD bgcolor="666699" colspan="2" width="494"><TABLE border="0" cellpadding="0" cellspacing="0" width="494"><TR><TD bgcolor="#039acc" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#039acc" height="1" width="492"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="492"></TD><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#039acc" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#0086b2" width="492"><FONT color="#ffffff" face="arial,helvetica,sanserif" size="+1"><IMG alt="" border="0" height="2" hspace="0" src="resources/void.gif" vspace="0" width="2"><B>Definition</B></FONT></TD><TD bgcolor="#017299" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#017299" height="1" width="492"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="492"></TD><TD bgcolor="#017299" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR></TABLE></TD></TR><TR><TD width="10"> </TD><TD width="484"><FONT color="#000000" face="arial,helvetica,sanserif"> |
| |
| <P>According to Michael Kay's "XSLT Programmer's Reference" page |
| 736, a predicate is "An expression used to filter which nodes are |
| selected by a particular step in a path expression, or to select a subset of |
| the nodes in a node-set. A Boolean expression selects the nodes for which the |
| predicate is true; a numeric expression selects the node at the position |
| given by the value of the expression, for example '[1]' selects the first |
| node.". Note that a predicate containing a boolean expression can |
| return zero, one or more nodes, while a predicate containing a numeric |
| expression can return only zero or one node.</P> |
| |
| </FONT></TD></TR></TABLE><BR> |
| |
| <TABLE border="0" cellpadding="0" cellspacing="0" width="494"><TR><TD bgcolor="666699" colspan="2" width="494"><TABLE border="0" cellpadding="0" cellspacing="0" width="494"><TR><TD bgcolor="#039acc" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#039acc" height="1" width="492"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="492"></TD><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#039acc" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#0086b2" width="492"><FONT color="#ffffff" face="arial,helvetica,sanserif" size="+1"><IMG alt="" border="0" height="2" hspace="0" src="resources/void.gif" vspace="0" width="2"><B>Examples</B></FONT></TD><TD bgcolor="#017299" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#017299" height="1" width="492"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="492"></TD><TD bgcolor="#017299" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR></TABLE></TD></TR><TR><TD width="10"> </TD><TD width="484"><FONT color="#000000" face="arial,helvetica,sanserif"> |
| |
| <P>I'll list a few examples that I can refer back to later on in this |
| document. All examples will use this XML document:</P><DIV align="right"><TABLE border="0" cellpadding="0" cellspacing="4" width="464"><TR><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#0086b2" height="1" width="462"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="462"></TD><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#0086b2" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#ffffff" width="462"><FONT size="-1"><PRE> |
| <?xml version="1.0"?> |
| <doc> |
| <foo location="Drumcondra"> |
| <bar name="Cat and Cage"/> |
| <bar name="Fagan's"/> |
| <bar name="Gravedigger's"/> |
| <bar name="Ivy House"/> |
| <foo> |
| <foo location="Town"> |
| <bar name="Peter's Pub"/> |
| <bar name="Grogan's"/> |
| <bar name="Hogans's"/> |
| <bar name="Brogan's"/> |
| </foo> |
| </doc></PRE></FONT></TD><TD bgcolor="#0086b2" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#0086b2" height="1" width="462"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="462"></TD><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR></TABLE></DIV> |
| |
| <P>Here are some examples of a predicate with boolean expressions:</P><DIV align="right"><TABLE border="0" cellpadding="0" cellspacing="4" width="464"><TR><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#0086b2" height="1" width="462"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="462"></TD><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#0086b2" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#ffffff" width="462"><FONT size="-1"><PRE> |
| <xsl:for-each select="//bar[contains(@name,'ogan')]"> |
| <xsl:for-each select="//bar[parent::*/@location = 'Drumcondra']"> |
| <xsl:for-each select="//bar[@name = 'Cat and Cage']"></PRE></FONT></TD><TD bgcolor="#0086b2" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#0086b2" height="1" width="462"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="462"></TD><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR></TABLE></DIV> |
| |
| <P>The first two select more than one node, while the last selects only one. |
| The last expression could select more nodes if the input document was |
| different. Now, here are a few examples of predicates with numeric |
| expressions:</P><DIV align="right"><TABLE border="0" cellpadding="0" cellspacing="4" width="464"><TR><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#0086b2" height="1" width="462"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="462"></TD><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#0086b2" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#ffffff" width="462"><FONT size="-1"><PRE> |
| <xsl:value-of select="//bar[1]"> |
| <xsl:value-of select="/doc/foo[2]/bar[1]"> |
| <xsl:value-of select="/doc/foo[2]/bar"></PRE></FONT></TD><TD bgcolor="#0086b2" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#0086b2" height="1" width="462"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="462"></TD><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR></TABLE></DIV> |
| <P>The last expression will return more than one node, but the step that |
| contains the predicate returns only one (the second <CODE><FONT face="courier, monospaced"><foo></FONT></CODE> |
| element).</P> |
| |
| <P>The above are the basic types of predicates. These can be grouped to create |
| a predicate pipeline, where the first predicate reduces the node-set that the |
| second predicate filters, and so on. Here are some examples:</P><DIV align="right"><TABLE border="0" cellpadding="0" cellspacing="4" width="464"><TR><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#0086b2" height="1" width="462"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="462"></TD><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#0086b2" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#ffffff" width="462"><FONT size="-1"><PRE> |
| A: <for-each select="//bar[contains(@name,'ogan')][2]"> |
| C: <for-each select="//bar[2][contains(@name,'ogan')]"> |
| B: <for-each select="//bar[position() > 3][2]"></PRE></FONT></TD><TD bgcolor="#0086b2" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#0086b2" height="1" width="462"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="462"></TD><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR></TABLE></DIV> |
| |
| <P>It is easier to figure out which nodes these expressions should return if |
| one goes through the steps and predicates one by one. In expression |
| <CODE><FONT face="courier, monospaced">A:</FONT></CODE> we first get all <CODE><FONT face="courier, monospaced"><bar></FONT></CODE> elements from the |
| whole document. Then the first predicate selects from that node-set only |
| those elements that have a <CODE><FONT face="courier, monospaced">@name</FONT></CODE> attribute that contains |
| "ogan", and we're left with these elements:</P><DIV align="right"><TABLE border="0" cellpadding="0" cellspacing="4" width="464"><TR><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#0086b2" height="1" width="462"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="462"></TD><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#0086b2" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#ffffff" width="462"><FONT size="-1"><PRE> |
| <bar name="Grogan's"> |
| <bar name="Hogans's"> |
| <bar name="Brogan's"></PRE></FONT></TD><TD bgcolor="#0086b2" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#0086b2" height="1" width="462"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="462"></TD><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR></TABLE></DIV> |
| <P>And finally, the last predicate then selects the second of those |
| elements:</P><DIV align="right"><TABLE border="0" cellpadding="0" cellspacing="4" width="464"><TR><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#0086b2" height="1" width="462"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="462"></TD><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#0086b2" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#ffffff" width="462"><FONT size="-1"><PRE> |
| <bar name="Hogans's"></PRE></FONT></TD><TD bgcolor="#0086b2" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#0086b2" height="1" width="462"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="462"></TD><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR></TABLE></DIV> |
| |
| <P>Expression <CODE><FONT face="courier, monospaced">B:</FONT></CODE> contains the same predicates as <CODE><FONT face="courier, monospaced">A:</FONT></CODE>, |
| but the resulting node set if completely different. We start off with the same |
| set of <CODE><FONT face="courier, monospaced"><bar></FONT></CODE> elements, but we apply the |
| <CODE><FONT face="courier, monospaced">"[2]"</FONT></CODE> predicate first, and end up with this |
| element:</P><DIV align="right"><TABLE border="0" cellpadding="0" cellspacing="4" width="464"><TR><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#0086b2" height="1" width="462"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="462"></TD><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#0086b2" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#ffffff" width="462"><FONT size="-1"><PRE> |
| <bar name="Fagan's"></PRE></FONT></TD><TD bgcolor="#0086b2" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#0086b2" height="1" width="462"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="462"></TD><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR></TABLE></DIV> |
| |
| <P>Fagan's is the bar where the Irish Taoiseach (prime minister) drinks his |
| pints, but its name does not contain the string "<CODE><FONT face="courier, monospaced">ogan</FONT></CODE>", |
| so the resulting node-set is empty.</P> |
| |
| <P>The third expressions also starts off with all <CODE><FONT face="courier, monospaced"><bar></FONT></CODE> |
| elements, applies the predicate "<CODE><FONT face="courier, monospaced">[position() > 3]</FONT></CODE>", |
| and reduces the node set to these:</P><DIV align="right"><TABLE border="0" cellpadding="0" cellspacing="4" width="464"><TR><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#0086b2" height="1" width="462"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="462"></TD><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#0086b2" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#ffffff" width="462"><FONT size="-1"><PRE> |
| <bar name="Ivy House"> |
| <bar name="Peter's Pub"> |
| <bar name="Grogan's"> |
| <bar name="Hogans's"> |
| <bar name="Brogan's"></PRE></FONT></TD><TD bgcolor="#0086b2" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#0086b2" height="1" width="462"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="462"></TD><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR></TABLE></DIV> |
| <P>The last predicate "<CODE><FONT face="courier, monospaced">[2]</FONT></CODE>" is applied to this node-set |
| and set is further reduced to:</P><DIV align="right"><TABLE border="0" cellpadding="0" cellspacing="4" width="464"><TR><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#0086b2" height="1" width="462"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="462"></TD><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#0086b2" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#ffffff" width="462"><FONT size="-1"><PRE> |
| <bar name="Peter's Pub"></PRE></FONT></TD><TD bgcolor="#0086b2" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#0086b2" height="1" width="462"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="462"></TD><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR></TABLE></DIV> |
| |
| </FONT></TD></TR></TABLE><BR> |
| |
| <TABLE border="0" cellpadding="0" cellspacing="0" width="494"><TR><TD bgcolor="666699" colspan="2" width="494"><TABLE border="0" cellpadding="0" cellspacing="0" width="494"><TR><TD bgcolor="#039acc" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#039acc" height="1" width="492"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="492"></TD><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#039acc" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#0086b2" width="492"><FONT color="#ffffff" face="arial,helvetica,sanserif" size="+1"><IMG alt="" border="0" height="2" hspace="0" src="resources/void.gif" vspace="0" width="2"><B>Categories</B></FONT></TD><TD bgcolor="#017299" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#017299" height="1" width="492"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="492"></TD><TD bgcolor="#017299" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR></TABLE></TD></TR><TR><TD width="10"> </TD><TD width="484"><FONT color="#000000" face="arial,helvetica,sanserif"> |
| |
| <P>From the examples in the last chapter we can try to categorize predicate |
| chains/pipelines to simplify our implementation. We can speed up processing |
| significantly if we can avoid using a data-structure (iterator) to represent |
| the intermediate step between predicates. The goal of setting up these |
| categories is to pinpoint those cases where an intermediate iterator has |
| to be used and when it can be avoided.</P> |
| |
| <TABLE border="0" cellpadding="0" cellspacing="0" width="484"><TR><TD bgcolor="666699" colspan="2" width="484"><TABLE border="0" cellpadding="0" cellspacing="0" width="484"><TR><TD bgcolor="#039acc" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#039acc" height="1" width="482"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="482"></TD><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#039acc" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#0086b2" width="482"><FONT color="#ffffff" face="arial,helvetica,sanserif"><IMG alt="" border="0" height="2" hspace="0" src="resources/void.gif" vspace="0" width="2"><B>Single predicate expressions</B></FONT></TD><TD bgcolor="#017299" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#017299" height="1" width="482"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="482"></TD><TD bgcolor="#017299" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR></TABLE></TD></TR><TR><TD width="10"> </TD><TD width="474"><FONT color="#000000" face="arial,helvetica,sanserif" size="-1"> |
| |
| <P>Expressions containing just a single predicate have no intermediate step |
| and there is no need for any extra iterator. The expression inside the |
| predicate can be applied directly to the original iterator. We call this |
| category <B>SIMPLE_CONTEXT</B>.</P> |
| |
| </FONT></TD></TR></TABLE><BR> |
| |
| <TABLE border="0" cellpadding="0" cellspacing="0" width="484"><TR><TD bgcolor="666699" colspan="2" width="484"><TABLE border="0" cellpadding="0" cellspacing="0" width="484"><TR><TD bgcolor="#039acc" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#039acc" height="1" width="482"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="482"></TD><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#039acc" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#0086b2" width="482"><FONT color="#ffffff" face="arial,helvetica,sanserif"><IMG alt="" border="0" height="2" hspace="0" src="resources/void.gif" vspace="0" width="2"><B>Expressions containing only non-position predicates</B></FONT></TD><TD bgcolor="#017299" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#017299" height="1" width="482"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="482"></TD><TD bgcolor="#017299" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR></TABLE></TD></TR><TR><TD width="10"> </TD><TD width="474"><FONT color="#000000" face="arial,helvetica,sanserif" size="-1"> |
| |
| <P>Predicate-order is significant when the predicate-chain contains one or |
| more predicate with an expression similar to |
| "<CODE><FONT face="courier, monospaced">position() > 3</FONT></CODE>" or "<CODE><FONT face="courier, monospaced">2</FONT></CODE>". This |
| is because the <CODE><FONT face="courier, monospaced">position()</FONT></CODE> and <CODE><FONT face="courier, monospaced">last()</FONT></CODE> explicitly |
| refer to the intermediate step between applying each predicate. The |
| expression:</P><DIV align="right"><TABLE border="0" cellpadding="0" cellspacing="4" width="464"><TR><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#0086b2" height="1" width="462"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="462"></TD><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#0086b2" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#ffffff" width="462"><FONT size="-1"><PRE> |
| <xsl:for-each select="//bar[contains(@name,'ogan')][parent::*/@location = 'Town']"></PRE></FONT></TD><TD bgcolor="#0086b2" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#0086b2" height="1" width="462"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="462"></TD><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR></TABLE></DIV> |
| <P>has two predicates that can be applied in any order and still produce the |
| desired node-set. Such predicates can be merged to:</P><DIV align="right"><TABLE border="0" cellpadding="0" cellspacing="4" width="464"><TR><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#0086b2" height="1" width="462"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="462"></TD><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#0086b2" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#ffffff" width="462"><FONT size="-1"><PRE> |
| <xsl:for-each select="//bar[contains(@name,'ogan') & (parent::*/@location = 'Town')]"></PRE></FONT></TD><TD bgcolor="#0086b2" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#0086b2" height="1" width="462"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="462"></TD><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR></TABLE></DIV> |
| <P>We call this category NO_CONTEXT.</P> |
| |
| </FONT></TD></TR></TABLE><BR> |
| |
| <TABLE border="0" cellpadding="0" cellspacing="0" width="484"><TR><TD bgcolor="666699" colspan="2" width="484"><TABLE border="0" cellpadding="0" cellspacing="0" width="484"><TR><TD bgcolor="#039acc" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#039acc" height="1" width="482"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="482"></TD><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#039acc" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#0086b2" width="482"><FONT color="#ffffff" face="arial,helvetica,sanserif"><IMG alt="" border="0" height="2" hspace="0" src="resources/void.gif" vspace="0" width="2"><B>Expressions containing position predicates</B></FONT></TD><TD bgcolor="#017299" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#017299" height="1" width="482"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="482"></TD><TD bgcolor="#017299" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR></TABLE></TD></TR><TR><TD width="10"> </TD><TD width="474"><FONT color="#000000" face="arial,helvetica,sanserif" size="-1"> |
| |
| <P>A predicate-chain, whose predicates' expressions contain any use of the |
| <CODE><FONT face="courier, monospaced">position()</FONT></CODE> or <CODE><FONT face="courier, monospaced">last()</FONT></CODE> functions require some way |
| of representing the intermediate step in an iterator. The first predicate |
| is applied to the original node-set, and the resulting node-set must then |
| be stored in some other iterator, from which the second predicate can get |
| the current position from the iterator's <CODE><FONT face="courier, monospaced">getPosition()</FONT></CODE> and |
| <CODE><FONT face="courier, monospaced">getLast()</FONT></CODE> methods. We call this category |
| GENERAL_CONTEXT</P> |
| |
| </FONT></TD></TR></TABLE><BR> |
| |
| <A name="exception"><!--anchor--></A> |
| <TABLE border="0" cellpadding="0" cellspacing="0" width="484"><TR><TD bgcolor="666699" colspan="2" width="484"><TABLE border="0" cellpadding="0" cellspacing="0" width="484"><TR><TD bgcolor="#039acc" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#039acc" height="1" width="482"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="482"></TD><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#039acc" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#0086b2" width="482"><FONT color="#ffffff" face="arial,helvetica,sanserif"><IMG alt="" border="0" height="2" hspace="0" src="resources/void.gif" vspace="0" width="2"><B>Expressions containing one position predicate</B></FONT></TD><TD bgcolor="#017299" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#017299" height="1" width="482"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="482"></TD><TD bgcolor="#017299" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR></TABLE></TD></TR><TR><TD width="10"> </TD><TD width="474"><FONT color="#000000" face="arial,helvetica,sanserif" size="-1"> |
| |
| <P>There is one expection from the GENERAL_CONTEXT category. If the |
| predicate-chain contains only one position-predicate, and that predicate is |
| the very first one, then that predicate can call the iterator that contains |
| the first node-set directly. Just look:</P><DIV align="right"><TABLE border="0" cellpadding="0" cellspacing="4" width="464"><TR><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#0086b2" height="1" width="462"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="462"></TD><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#0086b2" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#ffffff" width="462"><FONT size="-1"><PRE> |
| <xsl:for-each select="//bar[2][parent::*/@location = 'Drumcondra']"></PRE></FONT></TD><TD bgcolor="#0086b2" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#0086b2" height="1" width="462"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="462"></TD><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR></TABLE></DIV> |
| <P>The <CODE><FONT face="courier, monospaced">[2]</FONT></CODE> predicate can be applied to the original iterator |
| for the <CODE><FONT face="courier, monospaced">//bar</FONT></CODE> step. And so can the |
| <CODE><FONT face="courier, monospaced">[parent::*/@location = 'Drumcondra']</FONT></CODE> predicate as well. This |
| is only the case when the position predicate is first in the predicate |
| chain. These types of predicate chains belong in the |
| NO_CONTEXT category.</P> |
| |
| </FONT></TD></TR></TABLE><BR> |
| |
| </FONT></TD></TR></TABLE><BR> |
| |
| <TABLE border="0" cellpadding="0" cellspacing="0" width="494"><TR><TD bgcolor="666699" colspan="2" width="494"><TABLE border="0" cellpadding="0" cellspacing="0" width="494"><TR><TD bgcolor="#039acc" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#039acc" height="1" width="492"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="492"></TD><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#039acc" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#0086b2" width="492"><FONT color="#ffffff" face="arial,helvetica,sanserif" size="+1"><IMG alt="" border="0" height="2" hspace="0" src="resources/void.gif" vspace="0" width="2"><B>Design details</B></FONT></TD><TD bgcolor="#017299" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#017299" height="1" width="492"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="492"></TD><TD bgcolor="#017299" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR></TABLE></TD></TR><TR><TD width="10"> </TD><TD width="484"><FONT color="#000000" face="arial,helvetica,sanserif"> |
| |
| <P>Predicates are handled quite differently in step expressions and step |
| patterns. Step expressions are not implemented with the various contexts in |
| mind and use a specialised iterator to wrap the code for each predicate. |
| Step patterns are more complicated and CPU (or should I say JVM?) |
| exhaustive. Step patterns containing predicates are analysed to determine |
| context type and compiled accordingly.</P> |
| |
| <TABLE border="0" cellpadding="0" cellspacing="0" width="484"><TR><TD bgcolor="666699" colspan="2" width="484"><TABLE border="0" cellpadding="0" cellspacing="0" width="484"><TR><TD bgcolor="#039acc" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#039acc" height="1" width="482"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="482"></TD><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#039acc" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#0086b2" width="482"><FONT color="#ffffff" face="arial,helvetica,sanserif"><IMG alt="" border="0" height="2" hspace="0" src="resources/void.gif" vspace="0" width="2"><B>Predicates and Step expressions</B></FONT></TD><TD bgcolor="#017299" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#017299" height="1" width="482"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="482"></TD><TD bgcolor="#017299" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR></TABLE></TD></TR><TR><TD width="10"> </TD><TD width="474"><FONT color="#000000" face="arial,helvetica,sanserif" size="-1"> |
| |
| <P>The basic behaviour for a predicate is to compile a <B>filter</B>. This |
| filter is an auxiliary class that implements the |
| <CODE><FONT face="courier, monospaced">org.apache.xalan.xsltc.dom.CurrentNodeListFilter</FONT></CODE> interface. The |
| <CODE><FONT face="courier, monospaced">Step</FONT></CODE> or <CODE><FONT face="courier, monospaced">StepPattern</FONT></CODE> that uses the predicate will |
| create a <CODE><FONT face="courier, monospaced">org.apache.xalan.xsltc.dom.CurrentNodeListFilter</FONT></CODE>. This |
| iterator contains the nodes that pass through the predicate. The compiled |
| filter is used by the iterator to determine which nodes that should be |
| included. The <CODE><FONT face="courier, monospaced">org.apache.xalan.xsltc.dom.CurrentNodeListFilter</FONT></CODE> |
| interface contains only a single method:</P><DIV align="right"><TABLE border="0" cellpadding="0" cellspacing="4" width="464"><TR><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#0086b2" height="1" width="462"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="462"></TD><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#0086b2" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#ffffff" width="462"><FONT size="-1"><PRE> |
| public interface CurrentNodeListFilter { |
| public abstract boolean test(int node, int position, int last, int current, |
| AbstractTranslet translet, NodeIterator iter); |
| }</PRE></FONT></TD><TD bgcolor="#0086b2" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#0086b2" height="1" width="462"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="462"></TD><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR></TABLE></DIV> |
| |
| <P>The code that is compiled into the <CODE><FONT face="courier, monospaced">test()</FONT></CODE> method is the |
| code for the predicate's expression. The <CODE><FONT face="courier, monospaced">Predicate</FONT></CODE> class |
| compiles the filter class and a <CODE><FONT face="courier, monospaced">test()</FONT></CODE> method skeleton, while |
| some sub-class of the <CODE><FONT face="courier, monospaced">Expression</FONT></CODE> class compiles the actual |
| code that goes into this method.</P> |
| |
| <P>The iterator is initialised with a filter that implements this interface: |
| </P><DIV align="right"><TABLE border="0" cellpadding="0" cellspacing="4" width="464"><TR><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#0086b2" height="1" width="462"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="462"></TD><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#0086b2" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#ffffff" width="462"><FONT size="-1"><PRE> |
| public CurrentNodeListIterator(NodeIterator source, |
| CurrentNodeListFilter filter, |
| int currentNode, |
| AbstractTranslet translet) { |
| this(source, !source.isReverse(), filter, currentNode, translet); |
| }</PRE></FONT></TD><TD bgcolor="#0086b2" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#0086b2" height="1" width="462"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="462"></TD><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR></TABLE></DIV> |
| |
| <P>The iterator will use its source iterator to provide it with the initial |
| node-set. Each node that is returned from this set is passed through the |
| filter before returned by the <CODE><FONT face="courier, monospaced">next()</FONT></CODE> method. Note that the |
| source iterator can also be a current node-list iterator (if two or more |
| predicates are chained together).</P> |
| |
| </FONT></TD></TR></TABLE><BR> |
| |
| <TABLE border="0" cellpadding="0" cellspacing="0" width="484"><TR><TD bgcolor="666699" colspan="2" width="484"><TABLE border="0" cellpadding="0" cellspacing="0" width="484"><TR><TD bgcolor="#039acc" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#039acc" height="1" width="482"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="482"></TD><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#039acc" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#0086b2" width="482"><FONT color="#ffffff" face="arial,helvetica,sanserif"><IMG alt="" border="0" height="2" hspace="0" src="resources/void.gif" vspace="0" width="2"><B>Optimisations in Step expressions</B></FONT></TD><TD bgcolor="#017299" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#017299" height="1" width="482"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="482"></TD><TD bgcolor="#017299" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR></TABLE></TD></TR><TR><TD width="10"> </TD><TD width="474"><FONT color="#000000" face="arial,helvetica,sanserif" size="-1"> |
| |
| <TABLE border="0" cellpadding="0" cellspacing="0" width="474"><TR><TD bgcolor="666699" colspan="2" width="484"><TABLE border="0" cellpadding="0" cellspacing="0" width="474"><TR><TD bgcolor="#039acc" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#039acc" height="1" width="472"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="472"></TD><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#039acc" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#0086b2" width="472"><FONT color="#ffffff" face="arial,helvetica,sanserif" size="-1"><IMG alt="" border="0" height="2" hspace="0" src="resources/void.gif" vspace="0" width="2"><B>Node-value iterators</B></FONT></TD><TD bgcolor="#017299" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#017299" height="1" width="472"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="472"></TD><TD bgcolor="#017299" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR></TABLE></TD></TR><TR><TD width="10"> </TD><TD width="464"><FONT color="#000000" face="arial,helvetica,sanserif" size="-1"> |
| |
| <P>Some simple predicates that test for node values are handled by the |
| <CODE><FONT face="courier, monospaced">NodeValueIterator</FONT></CODE> class at runtime. These are:</P><DIV align="right"><TABLE border="0" cellpadding="0" cellspacing="4" width="464"><TR><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#0086b2" height="1" width="462"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="462"></TD><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#0086b2" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#ffffff" width="462"><FONT size="-1"><PRE> |
| A: foo[@attr = <value>] |
| B: foo[bar = <value>] |
| C: foo/bar[. = <value>]</PRE></FONT></TD><TD bgcolor="#0086b2" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#0086b2" height="1" width="462"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="462"></TD><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR></TABLE></DIV> |
| |
| <P>The first case is handled by creating an iterator that represents |
| <CODE><FONT face="courier, monospaced">foo/@attr</FONT></CODE>, then passing this iterator and a test-value to |
| a <CODE><FONT face="courier, monospaced">NodeValueIterator</FONT></CODE>. The <B><value></B> is an |
| expression that is compiled and passed to the iterator as a string. It |
| does <B>not</B> have to be a literal string as the string value is |
| found at runtime. The last two cases are similarly handled by creating an |
| iterator for <CODE><FONT face="courier, monospaced">foo/bar</FONT></CODE> and passing that and the test-value to |
| a <CODE><FONT face="courier, monospaced">NodeValueIterator</FONT></CODE>.</P> |
| |
| </FONT></TD></TR></TABLE><BR> |
| |
| <TABLE border="0" cellpadding="0" cellspacing="0" width="474"><TR><TD bgcolor="666699" colspan="2" width="484"><TABLE border="0" cellpadding="0" cellspacing="0" width="474"><TR><TD bgcolor="#039acc" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#039acc" height="1" width="472"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="472"></TD><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#039acc" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#0086b2" width="472"><FONT color="#ffffff" face="arial,helvetica,sanserif" size="-1"><IMG alt="" border="0" height="2" hspace="0" src="resources/void.gif" vspace="0" width="2"><B>Nth descendant iterators</B></FONT></TD><TD bgcolor="#017299" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#017299" height="1" width="472"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="472"></TD><TD bgcolor="#017299" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR></TABLE></TD></TR><TR><TD width="10"> </TD><TD width="464"><FONT color="#000000" face="arial,helvetica,sanserif" size="-1"> |
| |
| <P>The <CODE><FONT face="courier, monospaced">Step</FONT></CODE> class is also optimised for position-predicates |
| that are applied to descendant iterators:</P><DIV align="right"><TABLE border="0" cellpadding="0" cellspacing="4" width="464"><TR><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#0086b2" height="1" width="462"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="462"></TD><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#0086b2" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#ffffff" width="462"><FONT size="-1"><PRE> |
| <xsl:for-each select="//bar[3]"></PRE></FONT></TD><TD bgcolor="#0086b2" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#0086b2" height="1" width="462"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="462"></TD><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR></TABLE></DIV> |
| |
| <P>Such step/predicate combinations are handled by the internal DOM's |
| inner class <CODE><FONT face="courier, monospaced">NthDescendantIterator</FONT></CODE>.</P> |
| |
| </FONT></TD></TR></TABLE><BR> |
| |
| <TABLE border="0" cellpadding="0" cellspacing="0" width="474"><TR><TD bgcolor="666699" colspan="2" width="484"><TABLE border="0" cellpadding="0" cellspacing="0" width="474"><TR><TD bgcolor="#039acc" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#039acc" height="1" width="472"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="472"></TD><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#039acc" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#0086b2" width="472"><FONT color="#ffffff" face="arial,helvetica,sanserif" size="-1"><IMG alt="" border="0" height="2" hspace="0" src="resources/void.gif" vspace="0" width="2"><B>Nth position iterators</B></FONT></TD><TD bgcolor="#017299" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#017299" height="1" width="472"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="472"></TD><TD bgcolor="#017299" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR></TABLE></TD></TR><TR><TD width="10"> </TD><TD width="464"><FONT color="#000000" face="arial,helvetica,sanserif" size="-1"> |
| |
| <P>Similarly, the <CODE><FONT face="courier, monospaced">Step</FONT></CODE> class is optimised for |
| position-predicates that are applied to basic steps:</P><DIV align="right"><TABLE border="0" cellpadding="0" cellspacing="4" width="464"><TR><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#0086b2" height="1" width="462"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="462"></TD><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#0086b2" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#ffffff" width="462"><FONT size="-1"><PRE> |
| <xsl:for-each select="bar[3]"></PRE></FONT></TD><TD bgcolor="#0086b2" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#0086b2" height="1" width="462"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="462"></TD><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR></TABLE></DIV> |
| |
| <P>Such step/predicate combinations are handled by the internal DOM's |
| inner class <CODE><FONT face="courier, monospaced">NthPositionIterator</FONT></CODE>.</P> |
| |
| </FONT></TD></TR></TABLE><BR> |
| |
| <TABLE border="0" cellpadding="0" cellspacing="0" width="474"><TR><TD bgcolor="666699" colspan="2" width="484"><TABLE border="0" cellpadding="0" cellspacing="0" width="474"><TR><TD bgcolor="#039acc" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#039acc" height="1" width="472"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="472"></TD><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#039acc" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#0086b2" width="472"><FONT color="#ffffff" face="arial,helvetica,sanserif" size="-1"><IMG alt="" border="0" height="2" hspace="0" src="resources/void.gif" vspace="0" width="2"><B>Node test</B></FONT></TD><TD bgcolor="#017299" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#017299" height="1" width="472"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="472"></TD><TD bgcolor="#017299" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR></TABLE></TD></TR><TR><TD width="10"> </TD><TD width="464"><FONT color="#000000" face="arial,helvetica,sanserif" size="-1"> |
| |
| <P>The predicate class contains a method that tells you if it is a boolean |
| test:</P><DIV align="right"><TABLE border="0" cellpadding="0" cellspacing="4" width="464"><TR><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#0086b2" height="1" width="462"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="462"></TD><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#0086b2" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#ffffff" width="462"><FONT size="-1"><PRE> |
| public boolean isBooleanTest();</PRE></FONT></TD><TD bgcolor="#0086b2" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#0086b2" height="1" width="462"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="462"></TD><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR></TABLE></DIV> |
| |
| <P>This can be, but it currently is not, used by the <CODE><FONT face="courier, monospaced">Step</FONT></CODE> class |
| to compile in optimised code. Some work to be done here!</P> |
| |
| </FONT></TD></TR></TABLE><BR> |
| |
| </FONT></TD></TR></TABLE><BR> |
| |
| <A name="step-patterns"><!--anchor--></A> |
| <TABLE border="0" cellpadding="0" cellspacing="0" width="484"><TR><TD bgcolor="666699" colspan="2" width="484"><TABLE border="0" cellpadding="0" cellspacing="0" width="484"><TR><TD bgcolor="#039acc" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#039acc" height="1" width="482"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="482"></TD><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#039acc" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#0086b2" width="482"><FONT color="#ffffff" face="arial,helvetica,sanserif"><IMG alt="" border="0" height="2" hspace="0" src="resources/void.gif" vspace="0" width="2"><B>Predicates and StepPatterns</B></FONT></TD><TD bgcolor="#017299" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#017299" height="1" width="482"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="482"></TD><TD bgcolor="#017299" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR></TABLE></TD></TR><TR><TD width="10"> </TD><TD width="474"><FONT color="#000000" face="arial,helvetica,sanserif" size="-1"> |
| |
| <P>Using predicates in patterns is slow on any XSLT processor, and XSLTC |
| is no exception. This is why the predicate context is carefully analysed |
| by the <CODE><FONT face="courier, monospaced">StepPattern</FONT></CODE> class, so that the compiled code is |
| specialised to handle the specific predicate(s) in use. First we should |
| consider the basic step pattern.</P> |
| |
| <TABLE border="0" cellpadding="0" cellspacing="0" width="474"><TR><TD bgcolor="666699" colspan="2" width="484"><TABLE border="0" cellpadding="0" cellspacing="0" width="474"><TR><TD bgcolor="#039acc" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#039acc" height="1" width="472"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="472"></TD><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#039acc" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#0086b2" width="472"><FONT color="#ffffff" face="arial,helvetica,sanserif" size="-1"><IMG alt="" border="0" height="2" hspace="0" src="resources/void.gif" vspace="0" width="2"><B>Basic pattern handling</B></FONT></TD><TD bgcolor="#017299" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#017299" height="1" width="472"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="472"></TD><TD bgcolor="#017299" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR></TABLE></TD></TR><TR><TD width="10"> </TD><TD width="464"><FONT color="#000000" face="arial,helvetica,sanserif" size="-1"> |
| |
| <P>All patterns are grouped (by the <CODE><FONT face="courier, monospaced">Mode</FONT></CODE> class) according to |
| their <I>kernel</I>-node type. The kernel node-type is node-type of the |
| <B>last</B> step in a pattern:</P><DIV align="right"><TABLE border="0" cellpadding="0" cellspacing="4" width="464"><TR><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#0086b2" height="1" width="462"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="462"></TD><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#0086b2" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#ffffff" width="462"><FONT size="-1"><PRE> |
| <xsl:template match="foo/bar/baz"> ... <xsl:template></PRE></FONT></TD><TD bgcolor="#0086b2" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#0086b2" height="1" width="462"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="462"></TD><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR></TABLE></DIV> |
| |
| <P>In this case the type for elements <CODE><FONT face="courier, monospaced"><baz></FONT></CODE> is the |
| kernel type. This step is <B>not</B> compiled as a step pattern. The node |
| type is passed to the <CODE><FONT face="courier, monospaced">Mode</FONT></CODE> class and is used to place the |
| remainder of the pattern code inside the big <CODE><FONT face="courier, monospaced">switch()</FONT></CODE> statement |
| in the translet's <CODE><FONT face="courier, monospaced">applyTemplates()</FONT></CODE> method. The whole pattern |
| is then <B>reduced</B> to:</P><DIV align="right"><TABLE border="0" cellpadding="0" cellspacing="4" width="464"><TR><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#0086b2" height="1" width="462"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="462"></TD><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#0086b2" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#ffffff" width="462"><FONT size="-1"><PRE> |
| match="foo/bar"</PRE></FONT></TD><TD bgcolor="#0086b2" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#0086b2" height="1" width="462"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="462"></TD><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR></TABLE></DIV> |
| |
| <P>The <CODE><FONT face="courier, monospaced">StepPattern</FONT></CODE> representing the <CODE><FONT face="courier, monospaced"><bar></FONT></CODE> |
| element test is compiled under the appropriate <CODE><FONT face="courier, monospaced">case:</FONT></CODE> section |
| of the <CODE><FONT face="courier, monospaced">switch()</FONT></CODE> statement. The code compiled for the step |
| pattern is basically just a call to the DOM's <CODE><FONT face="courier, monospaced">getType()</FONT></CODE> |
| method and a test for the desired node type. There are two special cases |
| for:</P><DIV align="right"><TABLE border="0" cellpadding="0" cellspacing="4" width="464"><TR><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#0086b2" height="1" width="462"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="462"></TD><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#0086b2" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#ffffff" width="462"><FONT size="-1"><PRE> |
| <xsl:template match="foo/*/baz"> ... <xsl:template> |
| <xsl:template match="foo/*@[2]"> ... <xsl:template></PRE></FONT></TD><TD bgcolor="#0086b2" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#0086b2" height="1" width="462"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="462"></TD><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR></TABLE></DIV> |
| |
| <P>In the first case we call <CODE><FONT face="courier, monospaced">isElement()</FONT></CODE> and in the second case |
| we call <CODE><FONT face="courier, monospaced">isAttribute()</FONT></CODE>, instead of <CODE><FONT face="courier, monospaced">getType()</FONT></CODE>.</P> |
| |
| </FONT></TD></TR></TABLE><BR> |
| |
| <TABLE border="0" cellpadding="0" cellspacing="0" width="474"><TR><TD bgcolor="666699" colspan="2" width="484"><TABLE border="0" cellpadding="0" cellspacing="0" width="474"><TR><TD bgcolor="#039acc" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#039acc" height="1" width="472"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="472"></TD><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#039acc" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#0086b2" width="472"><FONT color="#ffffff" face="arial,helvetica,sanserif" size="-1"><IMG alt="" border="0" height="2" hspace="0" src="resources/void.gif" vspace="0" width="2"><B>Patterns with predicates</B></FONT></TD><TD bgcolor="#017299" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR><TR><TD bgcolor="#0086b2" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD><TD bgcolor="#017299" height="1" width="472"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="472"></TD><TD bgcolor="#017299" height="1" width="1"><IMG alt="" border="0" height="1" hspace="0" src="resources/void.gif" vspace="0" width="1"></TD></TR></TABLE></TD></TR><TR><TD width="10"> </TD><TD width="464"><FONT color="#000000" face="arial,helvetica,sanserif" size="-1"> |
| |
| <P>The <CODE><FONT face="courier, monospaced">typeCheck()</FONT></CODE> method of the <CODE><FONT face="courier, monospaced">StepPattern</FONT></CODE> |
| invokes a method that analyses the predicates of the step pattern and |
| determines their context. (Note that this method needs to be updated to |
| handle the exception to the GENERAL_CONTEXT metioned in the section |
| <A href="#exception">Expressions containing one position predicate</A> earlier in this document.) The <CODE><FONT face="courier, monospaced">translate()</FONT></CODE> method of the |
| <CODE><FONT face="courier, monospaced">StepPattern</FONT></CODE> class contains a <CODE><FONT face="courier, monospaced">switch()</FONT></CODE> statement |
| that calls methods that are tailored for compiling code for the various |
| predicate contexts.</P> |
| |
| </FONT></TD></TR></TABLE><BR> |
| |
| </FONT></TD></TR></TABLE><BR> |
| |
| </FONT></TD></TR></TABLE><BR> |
| |
| </TD></TR></TABLE></TD></TR></TABLE><BR><TABLE border="0" cellpadding="0" cellspacing="0" width="620"><TR><TD bgcolor="#0086b2"><IMG alt="dot" height="1" src="resources/dot.gif" width="1"></TD></TR><TR><TD align="center"><FONT color="#0086b2" size="-1"><I> |
| Copyright © 2004 The Apache Software Foundation. |
| All Rights Reserved. |
| </I></FONT></TD></TR></TABLE></BODY></HTML> |