I am attempting to generate the following diagram in latex:
I've been using the tikz package, which although its capabilities seem to be endless, it does have a rather steep learning curve. I am currently learning how to generate simple diagrams including circles, arrows, squares, and have no idea how to include text yet. I am working through the manual so I will eventually have a good understanding of the tool, but as of yet, the diagram shown is beyond my capabilities. Could someone specify how I should go around generating this diagram? Many thanks for your help.