Translated Footnotes — an Example of Objective Links
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The opposition between objective and subjective links proposed by Paul Kahn pertains most to legacy documents, such as works originally intended for print, including scientific papers and scholarly articles, dictionaries, and encylopedias -- all of which contain explicit reference structures, such as foot- and endnotes, glossaries, and "see also" or "viz." commands. All of these directions convert to hypertext links, and the conversion can be automated.
Subjective or associative links, in contrast, are added to the text by hypertextualizers or hypertext authors, but they often depend on the existence of newly available material and can rarely be based on document structure. They demand domain knowledge. A content expert or author (as opposed to a programmer) has to create them.