One of the key functions of library and information services is to provide access to information based on users' requests for knowledge. Knowledge can be stored in a wide range of information bearing objects such as text, image, sound, multimedia, and as technology develops more people gain access to the objects, through different media. We will here analyze the processes and problems associated with determining the subject matter of an information bearing object.
The linked paper is by Jens-Erik Mai, whose publications can be found here. Personally, I recommend studying his dissertation. At various times in the past, I have connected a C.S. Peirce scholar, Mary Keeler, to Steven Newcomb, one of the founders of the topic maps paradigm (among other important contributions). What we get from that coupling is the realization that there is, indeed, a semiotic aspect to the nature of subjects. From the linked paper: