Subject headings are consistent, descriptive key terms assigned across a body of information. With a controlled, limited, systematic, stylized use of words one can create a thesaurus, a controlled vocabulary for description and specific subject headings. Despite this an element of human bias is present in each record. Subject heading assignment is not an exact science. Currently there is a 4-volume set of these headings and every library that uses these subject headings will own a set of these volumes.
All proper names are subject headings.
Fiction is rarely assigned a subject heading. Same with poetry. The International Standard Book Number for the book. Each book is assigned a unique number. The first part of the number indicates the publisher and whether or not the publisher is American or not.