Precedence Property Pattern
Precedence Property Pattern
Intent
To describe relationships between a pair of events/states
where the occurrence of the first is a necessary pre-condition for
an occurrence of the second. We say that an occurrence of the second
is enabled by an occurrence of the first.
Example Mappings
In these mappings P is the consequent and S is
the enabling state/event.
Examples and Known Uses
Precedence properties occur quite commonly in specifications of
concurrent systems. One common example is in
describing a requirement that a resource is only granted
in response to a request.
Relationships
Note that a Precedence property is like a converse of a Response
property. Precedence
says that some cause precedes each effect,
and Response says that
some effect follows each cause. They are not equivalent, because
a Response allows effects to occur
without causes (Precedence
similarly allows causes to occur without subsequent effects).
Note that this pattern does not require that each occurrence of
a consequent will have its own occurrence of an enabling condition.
This is an Order pattern.