Elements: Controlling the order and the repetition (DataStage®)

Controlling the repetition of nested elements

In a given XML hierarchy, nested elements may repeat. The following example contains a list of cities in which a customer operates.


<directory>
   <customer name="Acme">
      <city>Boston</city>
      <city>Chicago</city>
      <city>New York</city>

On the input link, city values map to the hierarchy using the following XPath expression:


/directory/customer/city/text()

To enable the <city> element to repeat within the <customer> node, you need to define this XPath expression as the repetition path. To do this, identify the associated input column as the key.

Repetition applies to each node beneath the root element. Therefore, the <customer> element can also repeat. The final output typically depends on the repetition path and the order of the input rows. Two repetition paths can produce the same results.

Controlling the order of elements

If you want the XML document to conform to a schema that stipulates the sequence of elements (<xs:sequence>), you must order the XPath expressions on the input link accordingly. XML Output sets the position of an element based on its first occurrence in the set of XPath expressions.

The repetition path /directory/customer/city/text() is in effect, and the order of XPath expressions is as follows. Notice that the first occurrence of the node division precedes the first occurrence of the node city.

Column	XPath expression
`CUSTOMER`	`/directory/customer/@name`
`DIVISION`	`/directory/customer/division/text()`
`CITY`	`/directory/customer/city/text()`

The input data consists of four rows:

CUSTOMER	DIVISION	CITY
`Acme`	`Toys`	`Boston`
`Acme`	`Toys`	`New York`
`Acme`	`Chemical`	`Boston`
`Acme`	`Chemical`	`New York`

Because the node division precedes city, the output is as follows:


<directory>
   <customer name="Acme">
      <division>Toys</division>
      <city>Boston</city>
      <city>New York</city>
   </customer>
   <customer name="Acme">
      <division>Chemical</division>
      <city>Boston</city>
      <city>New York</city>
   </customer>
</directory>

If you reorder the XPath expressions, the result changes. For example, the XPath expression for CITY is now in the middle position:

Column	XPath expression
`CUSTOMER`	`/directory/customer/city/text()`
`CITY`	`/directory/customer/city/text()`
`DIVISION`	`/directory/customer/division/text()`

This reordering generates the following output:


<directory>
   <customer name="Acme">
      <city>Boston</city>
      <city>New York</city>
      <division>Toys</division>
         </customer>
   <customer name="Acme">
      <city>Boston</city>
      <city>New York</city>
      <division>Toys</division>
         </customer>
</directory>