Presents your  
XML AND WEB SERVICES E-NEWSLETTER for November 10, 2003 
 
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XSL TRANSLATES WEB SERVICES APPLICATIONS   
  
One common problem in Web services applications is that the back-end 
software doesn't support XML (or at least not the XML that your Web
services 
have standardized on). To defeat this problem, many architectures 
employ

a translation stage that deciphers the incoming XML and converts it to 
a

more appropriate format for the back-end systems. While there are many 
ways you can translate your XML to a different format, eXtensible 
Stylesheet Language (XSL) provides a robust, standard, and XML-friendly
solution. 
  
SOME COMMON PROBLEMS   
  
There are a variety of translations that might need to occur between 
the

XML message and the application that will process it. However, there 
are

also a handful of common problems, including:   
  
* Lookup   
* Mapping   
* Aggregation   
* Splitting   
* Formulas   
* Reordering   
  
Lookup processes take an incoming value and map it to a different value 
for the target system. For example, your XML has a value of 309, but 
the

application needs a value of "Uber Widget."   
  
Mapping essentially reassigns a value from one field to another. For 
example, in the XML, you might have an AccountNumber element that needs
to 
be assigned to a new element called CustomerAccountNumber.   
  
Aggregation is the process of grouping two or more items from the XML 
into a single item for the back-end system. A common example is the 
combination of first and last name fields into a single name field.
Splitting is 
the opposite of aggregation and involves decomposing an XML value into 
two or more discrete components.   
  
Formulas generally involve a computation on one or more XML values to 
arrive at a new value for the application. One example is calculating 
an

order total from subtotals in the XML.   
  
Finally, reordering is the process of changing the sequence or 
structure

of items in the XML so that they match the expected sequence or 
structure of the target system.   
  
A MAPPING EXAMPLE   
  
Let's examine this process in more detail using a simple example. We'll 
suppose that our incoming XML looks like LISTING 1.   
  
Listing 1: webserviceorder.xml   
  
<?xml version="1.0" ?>   
<Order>   
  <OrderNumber>8100</OrderNumber>   
  <AccountNumber>99213</AccountNumber>   
  <Item>   
    <SKU>2388</SKU>   
    <Description>Uber Widget</Description>   
    <Quantity>15</Quantity>   
    <PricePer>10.95</PricePer>   
  </Item>   
  <Item>   
    <SKU>6273</SKU>   
    <Description>Flangeoid</Description>   
    <Quantity>10</Quantity>   
    <PricePer>52.00</PricePer>   
  </Item>   
</Order>   
  
Now, our order system needs a slightly different format. What we want 
is

to convert the incoming order from the Web service to the format shown 
in LISTING 2.   
  
Listing 2: applicationorder.xml   
  
<?xml version="1.0" encoding="UTF-8" ?>   
<NewOrder>   
  <CustomerAccountNumber>99213</CustomerAccountNumber>   
  <CustomerOrderNumber>8100</CustomerOrderNumber>   
  <OrderItems>   
    <OrderItem>   
      <SKU>2388</SKU>   
      <CustomerPrice>10.95</CustomerPrice>   
      <Quantity>15</Quantity>   
      <Subtotal>164.25</Subtotal>   
    </OrderItem>   
    <OrderItem>   
      <SKU>6273</SKU>   
      <CustomerPrice>52.00</CustomerPrice>   
      <Quantity>10</Quantity>   
      <Subtotal>520</Subtotal>   
    </OrderItem>   
  </OrderItems>   
</NewOrder>   
  
THE TRANSLATIONS   
  
Since this is a simplified example, there are only a few things we need 
to do in our XSL template to translate our format. The first thing we 
notice is that we have to map a few elements:   
  
* Order to NewOrder   
* AccountNumber to CustomerAccountNumber   
* OrderNumber to CustomerOrderNumber   
* Item to OrderItem   
* PricePer to CustomerPrice   
  
Next, we need to reorder the OrderItem elements under a new element 
called OrderItems. Finally, we've added a new element called Subtotal
that 
contains a calculation based on the price multiplied by the quantity.   
  
The mapping translations are easiest because you simply define your new 
element in the template and specify that it have the value of an 
element

from the incoming XML document. The reordering of the Items is 
accomplished by putting the Item subtemplate call within a new element
called 
OrderItems. Finally, the calculation is handled using a simple XPath 
expression.   
  
LISTING 3 shows the XSL document used to convert from the incoming XML 
to the application-specific XML.   
  
Listing 3: translate.xsl   
  
<?xml version="1.0"  ?>   
<xsl:stylesheet version="1.0" 
xmlns:xsl=" http://www.w3.org/1999/XSL/Transform">   
  <xsl:template match="/">   
    <xsl:apply-templates select="Order" />   
  </xsl:template>   
  
  <xsl:template match="Order">   
    <NewOrder>   
      <CustomerAccountNumber><xsl:value-of select="AccountNumber"   
/></CustomerAccountNumber>   
      <CustomerOrderNumber><xsl:value-of select="OrderNumber"   
/></CustomerOrderNumber>   
      <OrderItems>   
        <xsl:apply-templates select="Item" />   
      </OrderItems>   
    </NewOrder>   
  </xsl:template>   
  
  <xsl:template match="Item">   
    <OrderItem>   
      <SKU><xsl:value-of select="SKU" /></SKU>   
      <CustomerPrice><xsl:value-of select="PricePer" /></CustomerPrice> 

 
      <Quantity><xsl:value-of select="Quantity" /></Quantity>   
      <Subtotal><xsl:value-of select="PricePer * Quantity" 
/></Subtotal>

  
    </OrderItem>   
  </xsl:template>   
       
</xsl:stylesheet>   
  
Brian Schaffner is an associate director for Fujitsu Consulting. He 
provides architecture, design, and development support for Fujitsu's 
Technology Consulting practice.   
  
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