[cap-talk] Another "core" principle

[Bill Frantz]

donnelley1 at webstart.com (Jed at Webstart) on Wednesday, December 20, 2006 wrote:

>At 03:19 PM 12/20/2006, Bill Frantz wrote:
>>shap at eros-os.com (Jonathan S. Shapiro) on Sunday, December 17, 2006 wrote:
>>
>> >I'm not sure my concern is valid, but I'm concerned about the membrane
>> >pattern. If the consequence of causally dependent capabilities (which is
>> >what membranes build) is that nobody ever dares to revoke a membrane,
>> >then there is absolutely no point introducing the membranes in the first
>> >place.
>>
>>The same issue applies to zapping space banks and the disk format
>>command.  There is no way to undo their destructive effects.
>>
>>Cheers - Bill
>
>While I don't know much about zapping space banks, I'm of course
>quite familiar with reformatting disks.  If I reformat a disk and that
>disk had meaningful user data that they need for their work, I go
>back to work and restore what I reformatted.
>
>In the message above you seem to suggest that if a revocation
>happens and it stops somebody from doing their work, that's
>OK.  If the revocation is as intended and the person should no
>longer have access, then of course it is more than OK, it's
>what should happen.

I didn't say it is OK to prevent people from doing their work.  What I
did say is that current systems have very destructive, non-recoverable
operations, and people have learned to live with them.

It is desirable to have an undo for most operations.  With some membrane
implementations, it is possible to turn the switch back on after
communications have been stopped.  Whether just turning things back on
would be effective depends on whether the objects affected can recover
when their access comes back.

Another approach would be to have a way of asking, "If I zap this
membrane/space-bank/disk, what will no longer function?"  Only one of
the problems here is giving the user an answer she can understand.

Cheers - Bill

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