For loosely coupled interoperability, the minimum we need is self- describing data, which is typed and represents correctly on each platform. XML does this very well. For many purposes, we can use a simple one-level XML generated from flat files, which is easily done with a Python or Perl script and involves no overhead. In any case, the open source languages sup- port powerful XML parsers. Different systems will use different schemata, but as long as we can identify fields, we can transform them from one XML schema to another. There are excellent XML parsers and libraries available for all the open source languages—notably, Perl, Python, and Java.