Audit Trails for XML documents and data: a DeltaXML solution
As the de facto standard for data and documents, XML is increasingly providing a format for data and documents that supply forensic evidence of laboratory results, designs or documentation. For such data a proper audit trail that records changes between versions is a vital piece of the forensic jigsaw.
There are many text-based change management and content management systems, but few offer the advantages that can be gained by having an XML-aware system to handle XML data.
Text-based data comparison systems can handle XML data, because it can be treated as text. But they will often identify large numbers of differences between two versions of an XML document simply because they are not aware of changes to XML markup which should be ignored when recording deltas. For example:
- XML attributes can appear in any order
- the XML file can be pretty-printed by adding white space which an XML parser will ignore
- namespace prefix values may differ.
In the above situations, a text-based data comparison program will flag changes that are irrelevant. The deltas will, therefore, be larger than necessary. and require significantly more storage space. Text-based deltas are only useful as a way of providing roll-forward and roll-back facilities: they are not useful as a record of changes because they do not retain any XML structure. This makes it almost impossible to use them for other purposes.
Using DeltaXML for audit trails has a number of advantages over text-based comparison systems. The first of these is, as mentioned above, that the deltas will be smaller and will not record changes that are simply due to re-formatting of XML data.
The second, and more important advantage, is that the deltas are themselves complete XML files, and so can be processed and interchanged as XML. With DeltaXML it is, for example, possible to determine directly from the delta files when a particular item of data changed - it is no longer necessary to re-generate all the intermediate versions of data to identify the version at which the change occurred. DeltaXML delta files provide an intelligent audit trail which can be used for many purposes, and not just for re-generating previous versions of data.
DeltaXML can enable you to gain even more advantages from converting your data to XML. Being able to represent any changes to your data in XML means that you can now automate processing of changes to your data.