Databases Reference
In-Depth Information
class Event inherits from object
attributes // attribute name attribute's data type,
subject objectList;
action actionList;
object objectList;
spatio_temporal_signature spatiotemp_instance;
end
As mentioned previously, it is important to provide the tools to the authors
for the definition of composite events. The composition of events in the con-
text of an IMD has two aspects:
Algebraic composition is the composition of events according to alge-
braic operators, adapted to the needs and features of an IMD.
·
Spatiotemporal composition reflects the spatial and temporal relation-
ships between events.
·
This chapter elaborates on the first aspect. Readers can refer to [5] for the
second one. First, however, we should define some fundamental concepts:
The spatiotemporal reference point (
q
) is the spatiotemporal start of
the IMD scenario named as
q
. This serves as the reference point for
every spatiotemporal event and instance in the IMD.
·
The temporal interval is the temporal distance between two events
(e
1
, e
2
), namely, the start and the end of the interval t_int :
·
(e
1
,e
2
),
where e
1
,e
2
are events that may either be attached to predefined tem-
poral instances relative to some reference or occur asynchronously.
==
Algebraic Composition of Events
In many cases, the author wants to define specific events that relate to other
existing events. We distinguish among the following cases: disjunction, con-
junction, inclusion, and negation.
Disjunction
e :
,
e
n
occurs. For instance, we may be interested in the event e occurring when
button A (e
1
) or button B (e
2
) was pressed.
==
OR(e
1
,
¼
,e
n
). This event occurs when at least one of the events e
1
,
¼
