Editorial: Blog Focus Change

Very briefly, and to provide fair warning to readers, the focus of this blog will begin changing in the upcoming months. The necessity to BUILD NIEM exchanges continues to be alive and well, however this need is being well served by a number of resources already. Instead, this blog will begin to focus on IMPLEMENTING NIEM exchanges through modern technologies and programming languages. For example, the first article you will see shortly focuses on using jQuery to parse an access NIEM-conformant data. If you have any suggestions or concerns, feel free to post them as comments here.

As a side note, and in the interest of full-disclosure, the author of this Blog, Joel Byford, has recently begun working at Microsoft Corporation as a part of their Public Sector consulting arm. He continues to be involved in national committees an standard-setting for information sharing, and is very excited to be working for such a prominent organization helping improve information sharing between public sector organizations.

Thank you so much for your ongoing readership and support!

XSLT: Select Distinct in XSL 1.0

cThe further one dives into XSLT, it may become necessary to extract a list of unique values from an XML document. This is commonly done in SQL through the SELECT DISTINCT statement, unfortunately, there is no direct equivalent in XSLT 1.0.

In order to perform this sort of functionality, one must leverage some of the more advanced aspects of XSLT including the preceding-sibling:: or another such "axis" as it's known in XSL.

To better understand, lets look at an example.  Given the following XSD snippet:

<?xml version="1.0" encoding="UTF-8"?>
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema">
    <xsd:element name="houseCategory" abstract="true"/>
    <xsd:element name="houseCategoryText" type="xsd:string" substitutionGroup="houseCategory"/>
    <xsd:element name="houseCategoryFlag" type="xsd:boolean" substitutionGroup="houseCategory"/>
    <xsd:element name="housePurchaseDateRepresentation" abstract="true"/>
    <xsd:element name="housePurchaseDate" type="xsd:date" substitutionGroup="housePurchaseDateRepresentation"/>
    <xsd:element name="housePurchaseDateTime" type="xsd:dateTime" substitutionGroup="housePurchaseDateRepresentation"/>
</xsd:schema>

The following XSLT will extract a list of unique substitutionGroup attribute values from above and list them in the output: 

<?xml version="1.0" encoding="UTF-8"?>
  <xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform" version="1.0" xmlns:xsd="http://www.w3.org/2001/XMLSchema" >
  <xsl:output method="xml" indent="yes"/>
  <xsl:template match="*">
    <xsl:for-each
        select="/xsd:schema/xsd:element/@substitutionGroup[not(. = ../preceding-sibling::xsd:element/@substitutionGroup/.)]">
        
        <xsl:element name="uniqueSubstitutionGroup">
            <xsl:value-of select="."/>
        </xsl:element>
        
    </xsl:for-each>    
  </xsl:template>
</xsl:stylesheet>

The resulting output would appear something like the following:

<?xml version="1.0" encoding="utf-8"?>
<uniqueSubstitutionGroup>houseCategory</uniqueSubstitutionGroup>
<uniqueSubstitutionGroup>housePurchaseDateRepresentation</uniqueSubstitutionGroup>

The information surrounding this question was sourced in part from information provided on Stack Overflow here.