The advent of electronic documents and the consequent creation of digital libraries has a profound impact on how we produce, organize, store, retrieve and consume information. All of these activities have been dictated to the present by the technologies used to share information; A change in the underlying technology, namely, the move from paper to electronic documents, offers a unique opportunity to revolutionize how information is disseminated. The same electronic document can be printed, spoken, spoken in outline form over telephone lines or the Internet, processed automatically to extract certain kinds of information, and so on. This paper will focus on a specific aspect of the opportunities opened up by electronic publishing -the ability to present information in multiple modalities and thereby free it from any single presentation medium.
But for all this to be realized, the electronic document has to be considered as the key component, not the printed page. The electronic document is not the representation of the printed form; the printed form is one/ representation of the electronic document. This means that the electronic document has to be written to convey explicitly as much structure as possible -and details of any one presentation medium, such as the spacing between paragraphs on a printed page and length of time between speaking sentences, have to be abstracted out of the electronic encoding.
Information present in traditional printed documents comes to life only when it is perused by the human reader. Intelligent processing of such information therefore requires explicit human intervention. Intelligent processing -computing- can range from performing symbolic calculations on mathematical expressions occurring in a document, to translating the information to alternative display formats, e.g.,audio, hypertext etc. To give a specific example, it requires a trained reader to make printed information available in spoken form[+]
Electronic communication, on the other hand, is mediated by an information processor rather than passive pieces of paper. This means that we can separate out the capture and storage of information from its presentation. Markup systems[+] like La)TeX capture the logical structure of a document along with its content. Rendering or presentation -the process of producing a ``display''- can be viewed as applying a specific set of transformations to the abstract logical structure encapsulated by the encoding.
Typically, the structure is visually formatted to produce visual layout, a rendering attuned to the eye's ability to rapidly access different parts of a two-dimensional display. Thus, visual rendering projects the document logical structure on paper in a form that enables the reconstruction of the structure envisioned by the author.
Before getting into details of aural presentation, it will be useful to talk about the difference between printed and spoken documents. The passive printed document is processed by an active reader, who can view it in many different ways -read only section titles, skip a piece of mathematics, temporarily skip to a different page to read a referenced theorem, reread an interesting passage, and so on. Such active processing becomes even more flexible when the document appears on a computer screen, because hypertext and calculational capabilities can be used.
When it comes to audio, on the other hand, the document/ is the active player and the human the passive one. The speaker (perhaps on an audio cassette) actively reads in a relentlessly linear fashion, from beginning to end, and the listener simply listens, with little control over the process. Further, producing audio documents can be a laborious and time-consuming task -just ask organizations like Recordings For the Blind (RFB), who are engaged in producing such `` talking books''[+].