Therefore, database entries of different types have different fields.For each entry type, the fields are divided into three classes: Omitting the field will produce a warning message and, rarely, a badly formatted bibliography entry.
You might not get the effect you want, however, if the very first character after the left brace is a backslash.
The ``special characters'' item later in this section explains.
Furthermore the strongest arguments for using the author-date system--like ``it's the most practical''--fall flat on their face with the advent of computer-typesetting technology.
For instance the Chicago Manual contains, right in the middle of page 401, this anachronism: ``The chief disadvantage of [a style like TEX, obviously, sidesteps the disadvantage.
The following are the standard entry types, along with their required and optional fields, that are used by the standard bibliography styles.
The fields within each class (required or optional) are listed in order of occurrence in the output, except that a few entry types may perturb the order slightly, depending on what fields are missing.
Consult the Local Guide to see what tools are available on your system.
The standard style's thirteen entry types do reasonably well at formatting most entries, but no scheme with just thirteen formats can do everything perfectly.
These entry types are similar to those adapted by Brian Reid from the classification scheme of van Leunen  for use in the Scribe system.
The meanings of the individual fields are explained in the next section.