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S T P   W O R L D   M O D E L
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The STP model requires two backward-compatible extensions related to
vendor orders: description of "service properties" and specification
of service preferences.


-= Service properties =-

We specify not only room properties, but also "service properties,"
which are the services that can be ordered for an event. We provide a
list for room and service properties in the STP world model; for each
property, we mark it as a "room property," "service property," or
"combined property." If the property is not marked, the system views
it as a room property, which ensures backward compatability.

() A "room property" is a property of a specific room, which cannot be
changed by vendor orders, such as the floor or maximal room capacity.
Every room property is either an integer (e.g. floor) or string (e.g.
building name).

() A "service property" describes service items that the system can
order, such as vegetarian meals or security personnel. Every service
property is an integer; it cannot be a string.

() A "combined property" is a property that may be part of the room,
and also may be ordered, such as projectors. Every combined property
is an integer.


-= Service preferences =-

For each event, we may specify PLF preferences for all properties,
that is, for "room," "service," and "combined" properties; note that
these PLFs may be uncertain. For example, we may specify a PLF for the
number of vegetarian meals or for the number of projectors. We may
also specify related event properties, and default rules that
construct preference PLFs from event properties.

When Optimizer generates a schedule, it ignores the PLFs for service
properties, and it uses only the "room part" of combined properties
in satisfying the related PLFs.