Monday, February 07, 2011

Just came back from FOSDEM. Felt really good to meet the “usual suspects” again. Thanks for the great weekend!

I also had a chance to talk with Jos about ODF Web and ODF Collaboration. Jos gave a great talk about his ODF Web Javascript Framework which emerged from his ODFKit efforts.
Jos had a very important slide in his talk which echoed my own believe: NO CONVERSION! This principle guided the design of his ODF Web Framework. NO CONVERSION simply means that Jos does not try to heuristically (aka lossy) map ODF to HTML and then map HTML heuristically (aka lossy) back to ODF. Instead Jos decided to have a clean 2-tier architecture which cleanly separates the content- and the view layer: ODF is content and HTML is the view. I think that’s the right approach. Even more: I think if you start adding “smart conversions”/”heuristics” and other “intelligent mappings” things will get ugly sooner or later. [And from my experience on filter hacking things will get messy sooner than you like. Always keep Murphy’s law in mind: What can go wrong will go wrong!].
We also had a chance to talk about Operational Transformation (OT) in the context of ODF. I tried to argue that what is really missing in ODF is a list of “atomic changes” a user can make to an ODF document. If we had this list of “atomic changes” we could build a transformation on top of it. For OT it is very important that you have “atomic” operations, since you need operation transformations for every pair of operation. E.g. if you have |OPS| operations you need |OPS x OPS| transformations. So keeping |OPS| small is quite important!
Assembling the list of atomic operations is a lot of work --- admitted. However it is work that every designer of an API needs to do anyway. I really believe that some input from the ODF API projects like Oracles’ ODFDOM, IBM’s Simple API for ODF, ANR’s LPOD and Jos’ ODFKit could really help.
Let me finish my post by a classification of change to an ODF document:

I believe that for change tracking we only need “atomic operations” and a way to combine them to “compound operations”. I don’t think we need to be able to track changes to the XML tree or the XML text. In fact I think it does more harm than good.