Agreed, there is some subtlety here we're still working on. Many materials also have properties that vary over some condition, for example temperature. I'm not positive how we'll handle that at this time, but we are thinking about it. For reference, we're looking to work with http://www.matweb.com/ so you can browse what data they have available for a few common cases like metals, composites, etc. and get an idea of the complexity we are trying to wrangle into something usable. Let me know if you have any ideas.