Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!tut.cis.ohio-state.edu!ucbvax!decwrl!decvax!schlep.dec.com!jfcl.dec.com!imokay.dec.com!borsom
From: borsom@imokay.dec.com (Doug Borsom)
Newsgroups: comp.editors
Subject: Re: multi-user editors.......
Keywords: why, how
Message-ID: <448@imokay.dec.com>
Date: 27 Apr 89 22:22:49 GMT
References: <8583@xanth.cs.odu.edu> <1523@sw1e.UUCP>
Reply-To: borsom@imokay.dec.com (Doug Borsom)
Distribution: usa
Organization: Digital Equipment Corp. Boxboro, MA
Lines: 35

In article <1523@sw1e.UUCP> uucibg@sw1e.UUCP (Brian Gilstrap [5-3929]) writes:
>...
>There is such and editor that runs under the MCP operating system on the
>Unisys (used to be Burroughs) A-series machines.  It probably doesn't quite
>qualify since the inherant assumption in this discussion seems to be that
>the full-screen editor is asynchronous (along the lines of emacs or vi). 
>....
>...However, this editor
>definitely allowed multi-user access, with granularity down to lines.  It also
>required that files have line numbers (ack!).
>....

Actually the Burroughs/Unisys editor can function in "patch" mode,
which allows any number of folks to work against the same base file. No
changes are made to that base file during the editing session.  For
each user, the editor records only the delta, the differences between
the base file and the changes that user made, although to the user,
it looks like he/she is changing the base file. As Brian notes,
the granularity is at the line level, and the editor uses line numbers
as an index into the files.  Each line is actually a record in the file.

After the editing session ends and the delta (patch) file is saved, the
delta file can be applied to the base file along with the delta files
of others who might have been editing the base file.  If conflicts arise
(two or more delta files alter the same record in the base file),
the utility that does the merging warns the user so conflicts can be
resolved.  A unique identifier is tagged onto the end of all the lines
in a delta file, in a non-text area of the record. This provides a
record of changes made to the base file.

The system is used (among other things) by system programmers working
on the Master Control Program, which is very powerful, very robust, and
is well over 600,000 lines long.  When I was with Unisys, there were
programmers  at sites on both coasts working on the MCP.  The editor
patch system allowed this to be done without total chaos ensuing.