A comment over at Lance's blog got me thinking about citations. To summarize, some anonymous commenter said that if a paper wasn't easily available online (specifically, "not available for free online (or through my acm portal subscription)") , they won't read or cite it, and then another commenter pointed out that it was the author's responsibility to acknowledge relevant work, give proper credit, and avoid duplicating previous work.
I certainly agree in spirit with the second comment, but I wonder, exactly, what are our responsibilities as authors? How much hunting, exactly, am I as an author expected to do to find relevant work? This is certainly an issue I've faced in my own work. For example, I've had the case where there may be a related article in an old Russian mathematics journal -- an article pops up in my search of related keywords and either the title or abstract seems potentially relevant, but I can't really tell without getting the article. So far, I've managed -- the blessings of always being near the Berkeley, Stanford, Harvard, or MIT libraries -- but it has sometimes been a non-trivial effort to track it down. In the old days, that library time was more or less expected. What expectations should there be in terms of tracking down old paper copies? What expectations should there be in terms of what an author is required to "spend" to get copies of possibly related work? I do think there is a reasonable argument that can be made that if your paper isn't freely available, an author can't necessarily be expected to cite it.
And of course I wouldn't have even faced the tracking problem except that I try to be diligent in my searches for relevant work. Working across areas, I've often found I have to spend some time guessing and doing some random walks to find out what people in another area call the concept I'm thinking about just to find the relevant papers. How much searching in Google/Google Scholar/your tool of choice should be expected of us? (I'm thinking here of the really annoying reviews I sometimes get of the form, "You should have cited this paper, I'm going to suggest rejecting your paper." That's inane. Perhaps I should have cited the paper, in which case, you should suggest that I cite the paper; that's what reviews are for.)
After all this, there's still the question of what should be cited. Science rules seem much "looser" than what I've seen in literature, history, etc. I'd never think of citing Karp or Garey and Johnson if I was showing a standard NP-completeness result (unless there was a very specific reason to do so) because it's now considered common knowledge. I think in many humanities fields that would be considered improper. Perhaps standards for various fields should be codified -- if only so that people in one field can easily understand the practices in another.