Four formats were identified: Plain, Preferred Presentation, Interchange and Interoperability formats. Their use and an informal description are given below for each of them.
Use: for e-mail, Emacs editing.
Informal description: This is a plain text representation, readable, writable and parsable, easily derived from the concrete syntax. Context-free parsing or context-sensitive parsing is applied to plain text representation to produce Abstract Syntax Trees.
Use: for reading in written documents on paper or screen.
Informal description: This is a graphical representation based on glyphs (digits, letters, symbols and special characters). It is the output format produced from the plain format by an Emacs editor, a pretty interactive structure editor, or LaTeX.
Use: for exchanging parsed CASL specifications or units (i.e. incomplete specifications).
Informal description: An interchange format defines a portable representation of CASL, allowing CASL documents to be transmitted between different products or machines. This is a textual representation of Abstract Syntax Trees. The interchange format should support attributes to encode layout information and other information which is not considered to be part of the structure of a CASL specification. It should support also the possibility to be dynamically enriched by new attributes. The proposed format is SGML text with some indexing method.
Use: for applying tools on CASL specifications.
Informal description: All tools defined on the interchange format should accept the interoperability format. A tool may require some attributes and ignore others. A tool must be able to work on a unit without any context. The format needs a basic mechanism for adding attributes. The proposed format is a slight generalisation of the interchange format: SGML with attributes that can be classified/typed according to tools requiring them.
For these different formats, several alternatives are explored: the Z interchange format based on SGML, the interchange format of annotated terms used in the new environment ASF+SDF, the SALSA interchange format.