Sorry if this feels like advertising, but it's made my scripting easier, so I wanted to share.
If you use AppleScript, particularly with OmniPlan, and can handle the adventure of using beta software, may I bring
ScriptDebugger 4.0.6b3 to your attention?
This recent release has a feature that makes it much easier to figure out what data is scriptable within OmniPlan documents. The Explorer window lets you browse down through the hierarchy of objects, to see not just documents currently open, but all the tasks and resources, and their properties too.