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From: calland@nosc-tecr ("CALLAND")
Newsgroups: net.lang.ada
Subject: Re: APSE Trends
Message-ID: <8606180229.AA02439@ucbvax.Berkeley.EDU>
Date: Tue, 17-Jun-86 15:36:00 EDT
Article-I.D.: ucbvax.8606180229.AA02439
Posted: Tue Jun 17 15:36:00 1986
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     I was very interested in the observation of Tony Alden on
porting tools in a production environment.  The Navy is currently
fielding its CMS-2 support software (MTASS) using a similar though
much less sophisticated technique.  MTASS is written in FORTRAN/77
with all host-dependent functions provided by the Common Interface
Routines.  The CIRs are written in a combination of FORTRAN and
assembly as appropriate for each host and emulate target computer
arithmetic (e.g., Floating Add for the AN/UYK-43) as well as the
normal i/o and other operations.

     Before the CIRs existed, it used to take 6 months to completely
rehost a revision release of MTASS (hosts include VAX/VMS, EXEC 8,
and of course the IBM OS's).  The rehosting time is now limited to
the amount of time it takes to ship the source tapes from the master
configuration management machine (EXEC 8) to the other hosts and
recompile them.

     Also the CIRs have now allowed a reduction in the amount of
certification testing performed on each rehost.  The full certification
test suite is performed on the master machine and a subset is performed
on each rehost.  With some exceptions due to the age of the code (parts
of which date back to 1975), there are so few porting problems that
it no longer is a concern.  But it has taken 3 years to reach this
level of confidence.

     This CIR approach has not been trouble-free.  Developing the
spec was very difficult and time-consuming.  There were at least
four false starts and this was starting from known requirements from
an existing system.  At least two protypes were constructed and
examined for interface design flaws.  And then implementation of
the production copy was worse.  As simple as the CIR interface is
(for the most part, the services are a subset of those provided
by FORTRAN/77), there were still problems in implementing the
complete interface and with keeping the interfaces compatible.
Suffice to say that, as a minimum, you must have experts for all
hosts to implement this type of software and you must get them
all together fairly often to ensure a compatible set of interfaces.

     The result has been successful for MTASS.  The CIRs themselves
are quite expensive but the costs of rehosting are quite low (with
much thanks due to ANSI).  CMS-2 applications developed using MTASS
have varying levels of transportability varying from complete (for
CMS-2 and assembler source code) to controlled (for Linkage Editor and
Tape Builder command streams) to user-dependent (for Simulator
command streams).  A File Exchange System provides the mechanism for
exchange of all MTASS file types (including object code, COMPOOLs,
and linked executables) between all hosts without foreknowledge of
the destination host.

     My conclusions are the CAIS is going to be successful but it
will take more work and money and time than the casual observer
might think and that the main obstacle to sharing and exchange of
significant software systems will be limited by legal and proprietary
restrictions rather than technical difficulties.  For examples of
the latter, I refer you to the restrictive notices that the USAF
places on its ICAM library and the disclaimer that Tony Alden placed
on his message regarding this subject.  You might also ask the
people responsible for the Navy's standard support software about
data rights and copyrights discussions they have with the Software
Engineering Institute and with SofTech; bring your lawyer as an
interpreter.

     Robert Calland
     NOSC

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