ACR - Process - Profile question

Question

Coming from a film/wet darkroom environment and being completely new to digital, I need help with a few concepts.
I think I understand ACR being akin to developers in film speak transforming RAW files to the basic digital "negative" that can be manipulated via LR to become the final print.  Different "developer" programs such as RPP can effect different effects on the negative such as Rodinal compared to Xtol on film.  In LR, this digital "negative" is presented somewhat differently depending what preview setting I choose:   minimal, standard, or 1:1.  Correct me if I am wrong.
Under Camera Calibration, how do the LR4/LR3 Processes:  2003, 2010, 2012  relate to the concept of the digital negative?  As the choices are under the Developer module, are they just different post processing effects that can be reversed if I choose another Process?  Or do they transform the DNG file at a pimary, permanent level, on which all other reversible post processing effects are added. 
Are the Profiles, Embedded or Adobe Standard (for the Leica M9) similar in concept where they are the initial color palattes that you start off with once ACR transforms the digital file into a photo?  Are they again reversible or more permanent?
As LR is non-destructive, I don't completely understand how the Processes and Profiles relates to the LR DNG file as changing my choices does affect the look of the photo.  Are they just added to the XMP file in adjustements to the DNG file or do they change the DNG file permanently?

Answer 1

Personally, I think the idea of "digital negative" is useful for introducing the idea of raw, but I think the analogy can quickly get stretched too far!  One major difference: with film, when you process the film, you change it from raw (unprocessed) film into negative or transparency.   The unprocessed film isn't there any more.  With raw, the raw image data is never (as far as I know) altered.  The output is a new processed image.  If it needs to be saved, it's saved to a new file (TIF, jpeg or some other format). 
Provided you keep the original raw file, then any processing effects can be reversed simply by going back to the original and processing it again. 
Some raw formats (including DNG) allow processing information to be stored as "metadata" in the file, but the image data is not changed.  That's a bit like saying that you write extra information on a piece of paper and put it in the envelope with the negative.  You've not altered the negative, you've just added extra information.  Lightroom stores edit information in the DNG that way, but the image data is not altered.  With proprietary raw files (Nikon NEF, Canon CR2 or whatever) it's not safe for anyone except the maker's software to write into the files, hence Adobe writes edit information into separate XMP files in those cases. 
Adobe has improved the overall raw processing several times, and hence there's the 2003 process, 2010 and now 2012 process.  Essentially each new version replaced the earlier ones.  However, there's a reason why they keep them all.  With Lightroom, the normal workflow is that the only file you keep is often the original raw file.  When you process it, Lightroom simply keeps a list of the edits and other changes you do.  Each time you display or print the image, Lightroom starts with the raw and does all the edits (it's pretty quick - near instantaneous).  But each process can give slightly different results.  So if you've processed an image in the 2010 process, then each time you display, print or export it, you need the 2010 process to do it. 
Hope that helps.