This question is a special case of this one, which has no satisfying answer in my opinion.
I often encounter papers that have been published twice (or more), without any modification. An example is this one. First presented at the DLS'12 conference, and published in the proceedings. Then, the proceedings have been published in an issue of the ACM SIGPLAN. Notice that the paper is the same, same DOI, etc. However, there are two bibtex entries (one
@article) which are similar, but not identical.
My question : in such cases, how should the paper be cited ? Using the
@inproceedings entry or the
(Side question : Why is it the case that a single paper is published twice ?)