[cap-talk] Petnames versus E-order with ocaps

[Karp, Alan H]

David-Sarah Hopwood wrote:
> > E-order guarantees the following property.  If Alice sends a message to Carol,
> > and then Alice sends a message to Bob containing a reference to Carol,
> 
> You mean "the same reference to Carol".

Alice says carol<-bar().  In a petname system, that's the only way she has to send a message to Carol.
> 
> > and Bob uses that reference to send a message to Carol, Carol will receive
> > the message from Bob after she receives the message from Alice.
> > (Did I get that right, MarkM?)
> 
> To avoid mistakes I suggest explicitly labelling the references, like
> this:
> 
>   If alice sends a message to carol on reference C, and then alice sends a
>   message to bob containing C, and bob uses C to send a message to carol,
>   carol will receive the message from bob after she receives the message
>   from alice.
> 
> (I prefer using lowercase names for subjects.)
>
I like that description.
> 
> > Here's where the versus comes in.  Bob would like to ensure that a
> > message he sends to Carol arrives after any messages Alice sent to
> > Carol before she sent Bob a reference to Carol.  In a petname system,
> > he can't do that if he had a reference to Carol before Alice sent him
> one.
> 
> That's not correct.
> 
> Use of a petname system does not mean that a subject (e.g. bob),
> cannot hold multiple distinct references to another subject
> (e.g. carol). It only means that the distinction between references
> will be lost when they are added to a petnamespace.
> 
> If bob wants to send a message on the reference that alice gave it,
> why would bob map the reference back to a petname, then forward to
> a potentially different reference? That would be unnecessarily
> complex.
> 
> If bob is a script written by some human Bob, then the scripting
> language will still presumably support lambda names as well as
> petnames.
> 
> If Bob is using direct manipulation in a GUI, then he can drag the
> depiction of the reference C from alice's message into the 'To' field
> of the message he is sending, and that should preserve the message
> ordering even if C is depicted as having the petname "foo".
> If Bob retypes "foo" into the 'To' field, then the system does not
> have enough information to preserve the ordering. Is that important?
> I think probably not.
>
You are describing a lambda name system where the fact that references are from different sources CAN be ignored.  I'm talking about a pure petname system, where the underlying infrastructure does the mapping automatically.

________________________
Alan Karp
Principal Scientist
Virus Safe Computing Initiative
Hewlett-Packard Laboratories
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