Almost every user of XML will, at some stage, need to do some form of comparison between different versions of their XML data or document. This could be because it is necessary to review the changes that have been made, or to check that the output from one version of some software is the same as the previous version, or to find changes so that they can then be processed in some other way.
Designers of XML formats often do not consider this requirement for comparison when designing an XML format. However, if this is taken into account at the design stage then it can make the usefulness of the XML greater and at the same time reduce the cost of developing software. This paper outlines some of the issues that can usefully be considered by XML designers to make comparison and change easier to handle. The design issues will also be of interest to any user of XML to provide a better understanding of processing change in XML.