Co-citations and co-links have long been used as measures of topical relatedness between documents in various datasets. However, there are some characteristic differences between co-citations in scientific literature and co-links in hypertext due to the underlying difference in the motivations for creating citations and links. While citations are created for formal scholarly communication, links are created for a variety of formal as well as informal purposes. We elaborate on these differences, and propose interpretations of a co-citation as an endorsement of a citation, and a co-link as an endorsement of a link. Such an interpretation is useful for focused or topical surfers to follow citations and links that are pertinent to a topic of interest in scientific literature and the web respectively.
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