How to choose the most worthwhile research papers to define my thesis? I'm a first year PhD student. I'm just reading background papers trying to find a topic for my thesis: my subject is turning around tree different elements (XML (as a tool), complex data, and the cloud computing (as an environment)). So I find that is a large subject with many materials that treat this subject, whether each element individually, or two elements at most at a time, but not all three together. 

My question is 


  How should I choose the most worthy materials so that I could find a good topic which uses these three elements together?


Any information, insights, or propositions are welcome. Thank you.
I can answer this from the perspective of someone who did it poorly in retrospect, but from a different field (engineering). You will want to make sure that any papers you begin with are:


Accepted findings in the field. I made the mistake of basing much of my thesis work on a paper which was used a one-off paradigm, and was not replicated by anyone other than myself. This resulted in my needing to spend much more time validating my results than I otherwise would have needed to, because there was no other validation in the literature.
Simplicity over novelty. You're a graduate student, at the beginning of your career. You'll have tons of time to do awesome things as your career progresses. Unless you're working for Dr. Awesome BigName Researcher whose lab is known for doing cutting-edge work on X, be conservative... choose the less exciting but more likely to work research over the more exciting but very complex and/or more likely to fail.


Note that this post is completely irrelevant to anyone whose advisor effectively tells them what their thesis project is, as your criterion will be (1) the papers your advisor hands you. You have my sympathies :)