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From a consumption point of view, the critical need in electronic document interchange is the ability to view, print, or read the document everywhere that someone has access to it. If the document can also be revised or edited then that is so much the better, but it is not required for use of the document.

Final Form and Revisable Form Interchange

There are two different ways to produce interchangeable electronic documents. Although there are many steps in the production of a visually rich document, the process of composition and layout partitions production into two parts. Composition and layout is the process which takes a representation of the content of a document and places that content onto a two-dimensional space (or sequence of two-dimensional spaces), usually called pages.

In the process of composition and layout, a number of decisions, called formatting decisions, are made: which fonts in which sizes and weights are used for which pieces of content, where on the page the content is placed, whether there are added content fragments such as headers and footers, and so on. These formatting decisions may be made automatically based on rules provided to the composition and layout process; they may be made by a human designer interacting with the composition and layout process; or they may be made using a combination of these two approaches.

The representation of the content before composition and layout is called revisable form. Revision is relatively easy because the formatting decisions have not been made or have only been tentatively made and can be revised when changes occur. The representation of the content after composition and layout is called final form.

The interchange of electronic documents can be done either in revisable form or in final form. If the revisable form is interchanged, then either the formatting decisions must be made entirely by the consumer of the electronic document or the rules for making the formatting decisions must be interchanged with the revisable form electronic document. If the first approach is chosen, then there is no way to guarantee how the document will appear to the consumer. Even if the second approach is chosen, existing formatting languages do not guarantee identical final form output when given the same revisable form input. Some formatting decisions are always left to the consumer's composition and layout software. Therefore, different composition and layout processes may produce different final form output.

The interchange of revisable form electronic documents can meet many authors' needs. Both the Standard Generalized Markup Language (SGML) and the HyperText Markup Language (HTML) are successfully used to interchange significant and interesting documents. But there are cases where these formats are not sufficient to meet the needs of the author. For these cases, interchange of final form electronic documents is necessary.

Requirement for Page Fidelity

The key problem with interchanging only revisable form documents is the inability to guarantee page fidelity. Page fidelity means that a given revisable form document will always produce the same final form output no matter where it is processed. There are a number of reasons why page fidelity is required.

The most obvious reason is that the composition and layout process involve a human designer's decisions. Only in the final form is it possible to capture these decisions. These formatting decisions are important in the presentation of the represented information. This is quite obvious in advertisements, where design plays an important role in the effectiveness of communicating the intended message. It is perhaps less obvious but equally important in the design of other information presentations. For example, the placement of text in association with graphical structures, such as in a map of the Washington, D.C., subway system (Figure 1), will greatly affect whether the presentation can be understood. In addition, formatting rules may not adequately describe complex information presentations, such as mathematics or complex tables, which may need to be hand designed for



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