Introduction

The central conceit of the DDC is that any given concept or topic has one correct number. Notes, tables of preference and other devices help guide choices between numbers which seem equally suitable. Where a classifier assigns a different number, we could fairly call this a mistake. But the DDC is a universal system, used worldwide. Not all communities organize knowledge in the same way. Any library or other institution using the DDC may choose to deviate from standard DDC if doing so better serves their users.

There is an inherent trade-off to such practices, in that local alterations lessen mutual compatibility with other institutions, even as they better serve local users. The DDC's Introduction speaks to this:

There are no ‘Dewey police’ that will come and reprimand any library that deviates from standard practice, but any library considering local notation should understand the implications of doing so.

Nevertheless, even standard DDC includes ‘official’ options, which chart a middle ground between unaltered DDC and completely local practices. Numbers from these options will be more readily comprehensible by other institutions, since they are described in the classification itself.

This chapter will examine the DDC's official options and discuss further local adaptations. For clarity's sake, ‘option’ in this chapter will always mean the official options and ‘local adaptations’ practices that go beyond anything spelled out in the classification; ‘alterations’ will refer to either or both of these together. ‘Local’ in the context of this chapter does not always mean one library and may refer to a group of similar libraries, perhaps even up to a national level in some cases.

Rationale

The DDC has a global user base and users from around the world participate in its development. Today, all development of the DDC has the aim of being the most useful classification system possible regardless of local context. But this necessarily means not all local priorities can be represented in standard notation.