O - Origin
Where did the source come from? Who is the author? When was this created? What is the context of this piece?
P - Purpose
Why does this piece exist? Why was it published? Who is the intended audience?
V - Value
What value does this source provide to my research? How relevant is it? How does it help you understand your topic?
L - Limitation
Where does this source fall short in helping you with your research? Is it biased?