Charles Ammi Cutter (1837-1903) published his Rules for a Dictionary Catalog in 1876. His "Objectives" still inform cataloging today.
1. To enable a person to fine a book of which either
A. the author)2. To show what the library has
B. the title) is known
C. the subject)
D. by a given author3. To assist in the choice of a book
E. on a given subject
F. in a given kind of literature
G. as to its edition (bibliographically)How we achieve these objectives is what you'll be learning about during the course of your training.
H. as to its character (literary or topical)