XSL Filter Operators
The filter operators are similar to the SQL Where clause. A filter is evaluated as a Boolean on every node that is within the current context. If the Boolean evaluates to true, the node is included in the returned set; otherwise, it's excluded. Filters are enclosed in brackets. Remember, in our discussion of XPath in Chapter 6, we used the following path to select certain elements:
/child::customer [attribute::customerID= c1] [position() = 1]
This path selects the first customer element from those customer elements that are siblings to the root element that has an attribute equal to c1. The first filter, [attribute::customerID=c1], filters out all the nodes that do not have a customerID attribute equal to c1. The second filter, [position()=1], filters out all the nodes except the node at position one. With XPath, we could rewrite the previous example as follows:
/child::customer [@customerID= c1] [1]
We will use this abbreviated form in XSL. There are also some expression operators that we can use when working with XSL. The expression operators are listed in the following table:
XSL Expression Operators
| Operator | Alternative syntax | Description |
|---|---|---|
| and | $and$ | Logical-and, shortcut is && |
| or | $or$ | Logical-or, shortcut is || |
| not() | $not$ | Negation |
| = | $eq$ | Equality |
| $ieq$ | Case-insensitive equality | |
| != | $ne$ | Not equal |
| $ine$ | Case-insensitive inequality | |
| < | $lt$ | Less than |
| $ilt$ | Case-insensitive less than | |
| <= | $le$ | Less than or equal |
| $ile$ | Case-insensitive less than or equal | |
| > | $gt$ | Greater than |
| $igt$ | Case-insensitive greater than | |
| >= | $ge$ | Greater than or equal |
| $ige$ | Case-insensitive greater than or equal | |
| $all$ | Set operation; returns TRUE if the condition is true for all items in the collection | |
| $any$ | Set operation; returns TRUE if the condition is true for any item in the collection | |
| | | Set operation; returns the union of two sets of nodes |
Using these operators, we can create filter patterns that are based on comparisons. We will do this in an example in the section "XSL Document Elements."