Concept XML XLST preceding-sibling and ancestor

Question

I am very new to xslt, and found it can be easy or complex. I want to make clear some concepts. What is preceding-sibling and what is ancestor, after searching from google,

Answer 1

The preceding-sibling:: axis

The preceding-sibling:: axis is an axis of navigation that includes all the preceding sibling elements to the focus element. By "sibling" we mean a different element which has the same parent to the reference item. By "preceding" we mean a node that occurs before the reference one. The order of the preceding-sibling axis is the reverse document order. Take a look at this document:

If the focus node is pear, then the sequence preceding-sibling::* is ...

1. apple
2. banana

Note: fruit, pear, lady-finger-banana and kiwi are not in the sequence.

So the following is true:

• preceding-sibling::*[ 1] is the apple
• preceding-sibling::*[ 2] is the banana
• count( preceding-sibling::*) is 2
• preceding-sibling::apple[ 1] is also the apple
• preceding-sibling::banana[ 1] is the banana
• preceding-sibling::*[ 3] is absent or the empty sequence

preceding-sibling::pop/ancestor::inventory/totalprice Example

We have to alter your sample document a little bit to usefully study this example

    
        
            
                $2.50
                20
            
            
                $1.50
                10
            
            
         
        $15  
    

Let us say the focus is on the element focus-item. To evaluate the expression preceding-sibling::pop/ancestor::inventory/totalprice follow these steps:

1. preceding-sibling::pop selects all the preceding pop elements to focus-item. This evaluates to a sequence of one node.

2. For each item in the left hand sequence (just one pop element it so happens), set this item as a temporary focus item, and evaluate the expression of the right of the / operator which is ...

   ancestor::inventory
   

   There is only one such node, which is the ancestral inventory node. Thus the first / operator evaluates to a sequence of one inventory node.

3. Now we evaluate the effect of the second / and its right-hand operand expression total price. For each item in the left hand sequence (just one inventory node so it happens), set this as a temporary focus item and evaluate totalprice.

4. totalprice is short for child::totalprice. There is only one total price element on the child axis of the temporary focus node, so the final result is a sequence of one node, which is the total price node.

Understanding by Diagrams

Here is a diagram for preceding-sibling::. In it the reference node is Charlie and the node on the preceding-sibling:: axis is in green. It is the only such node.