In the Dewey Decimal Classification (DDC) system, a Relative Index is a type of reference tool that is used to help users locate specific topics or themes within the classification system. A Relative Index is typically a list of terms or phrases that are related to a particular subject or topic, along with the corresponding decimal numbers that represent the class, category, or subcategory where that topic is discussed in the DDC system.
Relative Indices are an important part of the DDC system, as they allow users to locate specific topics or themes within the classification system even if they do not know the exact decimal number that represents that topic. They are typically organized alphabetically, and they may include cross-references to other terms or phrases that are related to the same topic.
In general, Relative Indices are used in conjunction with the main classes, subclasses, and categories of the DDC system to help users find and access specific information within the classification system. They are an important reference tool for librarians and patrons, and they are an essential part of the DDC system.