[cap-talk] A challenge for membranes

[Mark Miller]

I am having trouble understanding what kind of graph of policy
expressions you are thinking about. Do you have a motivating example
in mind?

On Feb 18, 2008 6:38 AM, Jonathan S. Shapiro <shap at eros-os.com> wrote:
> There is a problem with the membrane pattern that I do not recall seeing
> discussed.
>
> A membrane implements a single (set of) policies. To the extent that it
> does so, it implements the interests of some particular "manager" of a
> collection of rights.
>
> A single process may participate in operations where restrictions
> imposed by multiple managers may need to be respected.
>
> In consequence, it does not seem to me that the "cell" guarded by a
> membrane can successfully be viewed as an undivided entity.
>
> This raises a design challenge:
>
>   1. In order for a membrane to operate properly, it must impose
>      a boundary that can only be crossed by traversal of that membrane.
>      This can be generalized to strictly hierarchical arrangements of
>      membranes, but not to general graphs of membranes.
>
>   2. In any situation requiring that multiple membranes be honored
>      simultaneously, a general graph appears to be required.
>
> Is there any reason to believe that this apparent conflict is
> resolvable?
>
>
> shap
>
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-- 
Text by me above is hereby placed in the public domain

    Cheers,
    --MarkM