Databases Reference
In-Depth Information
Time Period Relationships
Along a Common Timeline
Excludes
Before
|-| |-|
Figure 14.22 T
1
[before] T
2
.
T
1
[meets] T
2
The predicate for this relationship, as it holds between two
points in time, expressed as points in time, is:
T
2
)
It says that T
1
comes immediately before T
2
.
The inverse of this relationship is: T
1
[meets
1
]T
2
. The predi-
cate for this relationship, as it holds between two points in time,
expressed as points in time, is:
((T
1
þ f
CTD(1))
¼
((T
1
-
f
CTD(1))
¼
T
2
)
It says that T
1
comes immediately after T
2
.
T
1
[
]T
2
The predicate for this relationship, as it holds between two
points in time, expressed as points in time, is:
equals
(T
1
¼
T
2
)
It says that T
1
and T
2
are equal if and only if they occur on the
same clock tick.
Time Period Relationships
Along a Common Timeline
Excludes
Meets
Meets
|-|-|
Figure 14.23 T
1
[meets] T
2
.
