Protagonist vs. subject
Typically in most reference works, information is sorted by more familiar Subject (i.e., topical) categorization systems.
However, another useful means of storing information (particularly in regards to keeping information (or goals) regarding various people or types of people, is through a protagonist categorization. This categorization can also often be simpler and more intuitive in certain areas.
Virtually all subjects can be reframed as protagonist(s).
For example, the Subject categorization of the field of "Medicine", might be considered as a study of medicines, healing, and also as dealing with hospitals, doctors, the body, etc.
At this site, to maximize access to a given page, the latter items could ideally be accessible from the topical Medicine page, but also through other Protagonist categorizations (e.g., doctors under "People by occupation", etc.)
This distinction has two main advantages:
1. In ensuring that "subject" (topical) terminology is confined to more mutually exclusive fields of study, easier overviews of all subjects can be had (e.g., physics and anthropology would be allowed whereas "person" would not--despite "person" being a protagonist). Imagine a university which has one "people" department and a "psychology" department--one might be confused as to where to go. Granted, questions are raised where "psychobiology" would be found--under psychology or biology, and it might be useful in rarer cases to delimit human psychology from any animal psychology. But normally, being forced to adhere to an overlap or refinement--not a miscellaneous grab bag, ensures we are not adding duplicate content. Subjects may be harder to innovate within--if a field doesn't exist, one would have to invent a name for it or find something "good enough". For example, if we wanted a subject for the psychology behind emoji use, we might be tempted to try "emoji psychology" if grab bags were allowed, but being forced to stick to recognized fields of study might lead us to note that "psycholinguistics" could cover "emoji" usage, with emojis just being an aspect if not subfield, and would also be useful to be discoverable by someone browsing psycholinguistic topics--unlike if "emoji psychology" were just added as another top-level topic or topic immediately within psychology).
2. With a scheme for individual entities of interest, though these might in areas inevitably be subcategorized by subject (e.g., "doctor", "medical technology", and "hospital" under "Medical protagonists"), they promote the exploration of very concrete items or entities--even without having to understand the confines of an abstract subject. For example, "light", "electricity", and "gravity" might be more immediately salient for people than "physics". It could also allow for greater language-independence and greater expansiveness in topics--while allowing browsers to know that "medicine" was not likely to be found as a protagonist (unless as a subcategorization of concept protagonists--i.e., subjects).
Note that while this mutual exclusivity is somewhat akin to faceted classification, fields of study like psychology and biology do not need to be mutually exclusive (A purely faceted subject-based scheme might instead have "cellular-level studies" vs. "organ-level studies" and "mind studies" vs. "body studies"; in this scheme, cellular studies combined with mind studies might be "cellular neuroscience".) While this doesn't allow for combineability of facets to make new ones, it still offers some of the cleanness of facets while encouraging the development of adequately descriptive (and ideally already familiar) succinct terms.
