Database Reference
In-Depth Information
[
τ
l
,
τ
h
]
∨
∨
∧
∧
E
E
1
;
;
:
:
;
+
;
+
:
+
[
τ
l
,
τ
h
]
E
1
E
1
E
2
E
2
E
1
E
1
E
2
E
2
E
1
E
1
E
2
E
2
E
1
E
1
E
2
E
2
E
1
E
1
E
1
(g)
(a)
(b)
(c)
(d)
(e)
(f)
Figure 4.2.
Graphical representations of the seven complex event constructors.
[10min]
;
E
3
:
+
[0.1sec, 1sec]
∨
E
1
E
2
Figure 4.3.
Graphical representations of an interval-constrained complex event E =
WITHIN(TSEQ
+
(E1
∨
E2, 0.1sec, 1sec); E3, 10min)
is a special artificial event used for querying the occurrences of non-
spontaneous events during a specific period, and is scheduled to happen
at an event node's expiration time.
3.4 RFID Complex Event Detection Methods
and Optimizations
Based on the defined specification language for complex RFID events,
the SASE framework [42] takes a query plan based method for complex
RFID event detection. SASE defines several operations including tem-
poral relationship, numerical constraints, negation and sliding window,
and six operators such as Sequence Scan and Construction (SSC), Se-
lection (
σ
), Window (WD), Negation (NG) and Transformation (TF).
These operations and operators are used to form complex RFID event
query plan in a bottom-up manner. An illustration for processing com-
Q
4
: EVENT SEQ(A x1, B x2,
¬
(C x3), D x4)
WHERE [attr1, attr2]
∧
x1.attr3 = '1'
∧
x1.attr4
>
x4.attr4
WITHIN T
Meanwhile, SASE also proposes some related query optimization strate-
gies, including Pushing Predicates Down (PPD) and Pushing Windows
Down (PWD) to tackle the issues of huge intermediate results and sliding
window constraints.
