the plain.bst style sorts the entries according to the name of their authors (using the alphabetical order14, of course), and, for papers by the same author(s), the year they have been published (the older first). The last criterion in case of equality is the title, being a little bit modified. If two references can’t be distinguished with the above, the first one being cited in the document appears first. Labels are numbers, starting with 1 14 The standard alphabetical order with 26 letters. Unfortunately, some language have a different alphabet, for instance Swedish, in which “å” and “ö” are considered as letters and placed after “z”
the alpha.bst style file is named alpha because it uses alphanumerical labels: Those labels are computed by BibTEX using the first three letters of the author name (or initials of the author names if multiple authors), followed by the last two digits of the publication year. Sorting the entries is done according to the label first, and then to the same criteria as for plain.bst, in case several publication have the same label15; 15You certainly don’t want that several publications have the same labels. Thus computing the labels is done in two phases: First computing the label with the standard method, and then adding a supplementary letter (“a”, “b”, ...) for multiple labels. And sorting is done just between those two phases...
you probably understood what unsrt.bst does: It does not sort its references, which appears in the order they are cited in the document. Everything else is done as in plain.bst;
abbrv.bst abbreviates first names of the authors and the names of predefined journal and month names. I forgot to mention that bibliography styles historically predefine some shorthands for computer science journal names (Oren Patashnik is a computer scientist...). Those shorthands are abbreviated journal names in this style file. These are the only difference between abbrv.bst and plain.bst
That’s all for classical styles. Those styles suffer from several problems, for instance not having a url field, or not being multilingual, or sorting in a weird way... Moreover, publishers often impose precise typographic rules for bibliographies. This entails that many other styles have been proposed. Let’s have a look at some of them.
apalike.bst was (also) written by Oren Patashnik. It uses a special construction for labels, generally called author-year. I think the best way to understand is with some examples:
Don’t forget to include the apalike.sty package when using the apalike.bst style: Indeed, if you remember how @biblabel and \cite are defined, you should have seen why... Moreover, labels created by apalike.bst might be long, and you probably will accept that LATEX hyphenates them if necessary, which the default \cite won’t do (cf. section 3). Also: There are some other author-year style files, named authordate1.bst, authordate2.bst, authordate3.bst, authordate4.bst, and that slightly differ from apalike.bst. They must be used together with the authordate1-4.sty package. Very last important thing: apalike.sty redefined \bibitem so that the optional argument becomes mandatory (but must still be within square brackets). But you probably don’t care since, of course, the bibliography style file tells BibTEX to always output it.
6.2.2 The natbib.sty package The natbib.sty package, written by Patrick W. Daly, goes a bit further: It mainly redefines \cite so that you can get author-year or numerical labels, in a very elegant way. Classical bibliography styles have been ported to natbib.sty, except alpha.bst since it already was an author-year style. The names of the ports are plainnat.bst, abbrvnat.bst et unsrtnat.bst. Moreover, those styles have a url field for adding reference to articles on the web. Also note that natbib.sty can be used with apalike.bst or authordate1.bst to authordate4.bst. Last interesting remark: There is a very clean documentation [Dal99c] for natbib.sty, it’s really worth reading. 16 6.2.3 The jurabib.sty package The package jurabib.sty, by Jens Berger, is another package for adapting the output to the typographic rules used in legal studies. It is associated to a bibliography style jurabib.bst, and rests on a very special format for the optional argument of \bibitem. It also redefines \cite, and defines many flavors of that command. See [Ber02] for detailed comments on jurabib.sty. 6.2.4 custom-bib Since there are many possible criteria for defining a bibliographic style, Patrick W. Daly decided to write a little piece of software for automatically generating customized bibliography styles. It asks you about 20 questions and produces a pretty ready-to-use bibliography style file. As usual with Patrick Daly, the documentation [Dal99b] is excellent, and I won’t go any further in the details. I just mention how to create your .bst-file: Simply type latex makebst.tex, and answer the questions. All along the execution, the style file is being created. It’s really easy and intuitive.