Presents your 
XML E-NEWSLETTER for September 27, 2002

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ACCESSING MULTIPLE DOCUMENTS WITH XSLT

This special TechMail delivers the skills and know-how so you can 
manage the needs and support the demands of the XML working environment. Below
is a sample of what you'll find on the DEVELOPER'S GUIDE TO XML CD-ROM.
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Extensible Stylesheet Language Transformations (XSLT) provides a robust
set of functions for transforming one XML document into another. This 
is particularly useful when incoming or outgoing XML documents don't match
the document type expected by the target system. There are many times 
when the target system might expect a single document even though the source
data is being distributed across multiple documents. We can solve this
problem by using XSLT to transform multiple-source documents into a 
single XML document.

A SAMPLE PROBLEM

We'll start by defining a simple scenario to illustrate the problem.
Assume our customers are going to send us their orders using XML 
documents.
We want to protect the price information in the XML documents because
different customers have different negotiated prices, which can change
often. Rather than put a per-item price in the XML, the customers will 
enter the price code for the particular item. For simplicity, we'll say that
there are five price codes being used based on the letters A through E. 
Each price code corresponds to the dollar amount listed in our proprietary
Price.xml document, which we update regularly. Unfortunately, our 
target order system doesn't understand Price.xml. Instead, it expects each 
line item in the order to have a real price value when input into the 
system.

THE ORDER

As the orders come in, we want to translate the <PriceCode> element 
into
a <Price> element. We'll do this using XSLT's document() function and 
an
XPath expression to extract the correct price code.

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THE DOCUMENT() FUNCTION AND XPATH

Using the document() function, you can access multiple XML documents
from within your XSLT template. You can open as many documents as you 
need.
The basic process we'll use to open and access external documents is to
assign the <PriceCodes> node of the Price.xml document to a variable
inside the translation and then use XPath to query that node for the
particular price.

To open a document and assign it to a variable, use the following 
syntax
in your XSLT template:

<xsl:variable name="prices" select=

"document('Price.xml')/PriceCodes"/>

This will open the Price.xml document in the current directory, find 
the
<PriceCodes> node, and assign it to the prices variable. Now we can
query this node to extract a price for a particular code using XPath. 
To
translate the price code into the price, you would use something like 
the
following:

<xsl:variable name="letter" select="PriceCode">

<xsl:value-of select=

"$prices/Code[Letter=$letter]/Price"/>

This extracts the value of the PriceCode from the input document into a
variable called $letter. Then, it uses the $letter variable to identify 
a
particular price using an XPath query. Below is a snippet of our XSLT
template that will put all of this together.

<xsl:variable name="prices" select=

"document('Price.xml')/PriceCodes"/>

<xsl:template match="Item">

<xsl:variable name="letter" select="PriceCode">

<Item>

  <SKU><xsl:value-of select="SKU"></SKU>

  <Quantity><xsl:value-of select=

"Quantity"></Quantity>

  <Price><xsl:value-of select=

"$prices/Code[Letter=$letter]/Price"/> </Price>

</Item>

</xsl:template>

AN EASY WAY TO GATHER YOUR INFO

Using XSLT templates to translate XML documents can be a very powerful
way to move data from one system to another. Sometimes, this can be
challenging if the source data is in multiple documents. You can use 
XSLT's
document() function to access the data in multiple XML documents to 
solve this problem.

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