subject classification
From Physics wiki
Subject Classification
Fortunately Library Science has already done some work for us here, and the Physical Review maintains the Physics and Astronomy Classification Scheme (PACS) and it seems prudent to work with this model somehow. Subject areas should strive to conform to the PACS classification, though names might vary slightly for reasons of practicality. However, any page may be placed in the respective category, e.g., [[:Category:PACS:11.10.Gh]] places in and links to Category:PACS:11.10.Gh. Unfortunately names and codes change, so this isn't going to be an exact science.

