Taxonomy of Facets & Composites

[Tyler Close]

Markm wrote:
> To recap the terminological points in this document:
>
> At the "laws of physics" level, there are only objects, not
> facets or
> composites.  An object is a combination of state and
> behavior.  Using Norm's
> note, I'd further say that the behavior computes new state
> and outgoing
> messages as a function of the current state and the
> incoming message.  An
> object reference refers to a given object.  An object only
> has one object
> reference.  (Or, all object references to the same object
> are equivalent.)

An elaboration of 'equivalent' should be included.

All references to an object are 'equivalent' in that they refer to
exactly the same thing and that that thing will respond in the same
way to exactly the same set of messages for all references.

An object may have many references that may or may not respond to an
EQ message (ie: two references to the same object are equivalent, but
the holder may have no way of knowing that they are equivalent). If
the holder has access to the innards of the reference, those innards
may differ between references to the same object.

The validity of two references to the same object may change
independently. (ie: one may become invalid while the other remains
valid).

> A capability == an object reference in an system with object-level
> capability security.

Maybe a better way to say this: "In a system with object-level
capability security, the word 'capability' is a synonym for
'reference'. The new word is introduced to emphasize that a capability
obeys more constraints than a reference in a non-capability system."

Tyler


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