Re: [CoFI] Language Design - Proposed Changes to CASL

[Till Mossakowski <till@informatik.uni-bremen.de>]

Dear Peter,

I like the new idea of having registered libraries (replacing the
former URLs) very much. I assume that this idea implies that there
will be some central procedure for registration of libraries.
Now I want to make the following three points:

1. What about version control? It should be possible to access both
   the latest version (say, by default) and earlier versions (say,
   by giving explicit version numbers). I assume that all older versions
   are kept, for the case of upwards compatibility problems.
   [Right. But it may be adequate to use the date as a version number when
    referencing specifications in a remote library, ignoring changes after
    the specified date.  --PDM]

2. There hopefully will be a lot of registered libraries. It is therefore
   very important to have a structured name space for them, say like
   a file system directory structure. Probably there will be central 
   library web pages also following this structure, helping the user
   to get a structured overview over the existing libraries
   (I think that search engines are only complementary and cannot
   replace this).
   [My suggestion would be to rely on simple, suggestive names to start
    with, and provide a means for introducing more structured synonyms at
    a later stage.  --PDM]

3. How is it possible to access an unregistered library (i.e. a local
   library still under development, which definitely should not be
   registered yet)?
   [Perhaps using the directory name, e.g., "/users/till/...", which
    tools would interpret locally.  --PDM]

My proposal:

LIB-NAME	::= local SIMPLE-ID    -- structure dependent on file system
		  | global LIB-ID VERSION?   -- latest version as default

LIB-ID		:: = lib-file SIMPLE-ID
		   | lib-dir-file SIMPLE-ID LIB-ID  
			-- concrete syntax: SIMPLE-ID "/" LIB-ID

VERSION		::= version NUMBER NUMBER	
			-- concrete syntax: NUMBER "." NUMBER


Greetings,
Till

[Peter has not yet found time to write his promised Note with details
 of the envisaged methodological aspects of libraries.  Your comments
 are very welcome, and may prompt the appearance of the note - once
 the documentation of the rest of CASL v0.99 has been finalized.  --PDM]