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5 Markup and display formats

Given an SGML specification S with the corresponding S-CASL-DTD it is possible to define many different output formats. First, note that SGML as such does not define any processing or output formatting. Second, note that there is not even a presentation symbol associated with the elements of the specification. These will have to be provided, as well as information on the larger structures of the encoded specification. It would seem natural to provide some standard styles for the presentation of the elements of the CASL language itself, and then for every specification S, the specific symbols and their layout has to be defined.

Presentation symbols available in the basic character set are easy to describe. To allow a richer choice of symbols, such as those needed for mathematical notation, we have to choose how to name the symbols. BKB-CASL suggests using symbols available in Latin-1, extended with CASL-specific names (modeled on Z notation). Other alternatives are to tap into existing identification schemes such as latex, ISO UCS, or vendor-specific schemes like the font/symbol selection on the macintosh.

The next matter for a presentation is where to place symbols with respect to each other. On a 2-dimensional display surface, such as paper or computer screen, every symbol is surrounded by 8 easily identified positions (clockwise they are: above, above-right, right, below-right, below, below-left, left, and above-left) which may be used for parameters. If we consider a symbol as a string of glyphs, every extra glyph in the string adds 5 possible extra positions usable for parameters. If we may consider a glyph as being hollow, e.g. a box, we also have the interior of the glyph as yet another parameter position. For a linear display surface, such as data file, every symbol is surrounded by only 2 positions (left and right, giving rise to postfix, prefix and infix notation), and having a string of glyphs only adds an extra position for every additional glyph in the string (mixfix notation). In the same manner as the output symbol for every element has to be specified, either by the specifier or by some system convention, so the parameter positions have to be specified. This can be seen as a task for the specifier, but can also be left to the suppliers of the CASL formatting information for various SGML-formatters. The standards should take into account that certain common symbols have standard positions for arguments. The formatting definitions will also allow the use of varying font sizes for different argument positions. BKB-CASL suggests a linear notation with indications for formatting, by using strings ` and ' to indicate positions above-right and below-right in the two-dimensional case, and a mixfix notation scheme for left, right and between glyphs argument positions.

CoFI Note: T-1 ---- 7 April 1997.
Comments to Magne.Haveraaen@ii.uib.no