There can be more than way to say the same thing, for example gramophone record, phonograph record and vinyl records. When libraries write catalog records they pick one of these terms and sticks to it, they use what is known as a ‘controlled vocabulary‘. This makes it easier to browse library catalogs.
Traditionally it has been thought that patrons want to browse by author and subject headings, so these fields have been controlled. The data in these fields can be used in other ways, Ross Singer has been experimenting with geographic subject headings.
Publisher is an uncontrolled field. Penguin and Penguin Books are the same publisher, but their name has been entered in catalog records differently, making it difficult to browse by publisher.
A workaround is to use the ISBN field in the catalog record. Almost every book published since 1970 has an ISBN. English-language books start with a 0 or 1, followed by a variable-length publisher code, item number and finally a checksum digit.
For example: 0-14-043531-X
0 = English language
14 = Publisher code
043531 = Item number
X = checksum
We are able to build a list of ISBN publisher codes by picking the most popular publisher name, as it appears in library records, for each code. Using ISBN we can start the process of making publisher a controlled field.