You have very limited time. 45 minutes goes very quickly. Please don't waste it.

This is a very high level audience. Chances are they know as much or more about the background material as you do. Please don't spend more than 10-12% of it (about five minutes max) on reviewing the background. They want to hear about the new things you've invented or discovered. They already know about what's gone before.

Obviously this depends on the subject matter. If your talk depends deeply on some detailed aspect of middle high German typography, you might need a little more time
reviewing the background for your contribution; but on XML and markup matters no long review is required.

--Retrieved from XML.hack