[e-lang] What is defensive consistency?

[Karp, Alan H]

David Wagner wrote:

> Ok so far, I think, but what's the definition of a client?  I used the
> names Xavier and Yolanda to refer to some unspecified 
> entity(entities),
> but who/what are those entities and what is the granularity 
> of a client
> entity?  How do I tell when an object or pair of objects 
> should count as
> two different clients as opposed to a single client?  Put another way,
> what is the granularity of the failure domain?
> 
I have always assumed that what makes two clients different is the
capability they use to access the object.  Basically, if the
capabilities the clients use could be separately revokable, then the
clients are different.  (I don't want to say "are not EQ" with Dean
listening in.)  I don't know if this distinction is what MarkM had in
mind, but I think it covers most of the cases in David's note.  The only
alternative I can think of, that every valid request returns a valid
result but that an invalid request may not, does not appear to be
consistent with MarkM's example.

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Alan Karp
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Virus Safe Computing Initiative
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