Logical Patterns

Logical patterns match events that arrive in temporal order and correlate them with logical relationships such as AND, OR and NOT.

Syntax

INSERT INTO <output stream>
SELECT <event reference>([event index])?.<attribute name>, ...
FROM (every)? (NOT)? <event reference>=<input stream>[<filter condition>]
          ((AND|OR) <event reference>=<input stream>[<filter condition>])? (within <time gap>)? ->  
    ...

Logical Pattern Keywords

Keywords such as AND, OR, or NOT can be used to illustrate the logical relationship.

Keyword	Description
AND	This allows both conditions of AND to be matched by two events in any order.
OR	The state succeeds if either condition of OR is satisfied. Here the event reference of the other condition is null.
NOT <condition1> AND <condition2>	When NOT is included with AND, it identifies the events that match <condition2> arriving before any event that match <condition1>.
Not <condition> FOR <time period>	When NOT is included with for, it allows you to identify a situation where no event that matches <condition1> arrives during the specified <time period>. e.g.,from not TemperatureStream[temp > 60] for 5 sec.

Here the NOT pattern can be followed by either an AND clause or the effective period of NOT can be concluded after a given <time period>. Further in Stream more than two streams cannot be matched with logical conditions using AND, OR, or NOT clauses at this point.

Example

This stream worker sends a stop action on the regulator if a removed action is triggered in the RoomKeyStream stream.

Stream Worker Code

-- Defines `RegulatorStateChangeStream` having information of regulator state change such as `deviceID`, `roomNo`, `tempSet`, and `action`.
CREATE STREAM RegulatorStateChangeStream(deviceID long, roomNo int, tempSet double, action string);

-- Defines `RoomKeyStream` which contains the events related to room key usage.
CREATE STREAM RoomKeyStream(deviceID long, roomNo int, action string);

-- Defines `RegulatorActionStream` which contains the events related to regulator state changes.
CREATE SINK RegulatorActionStream WITH (type='log') (roomNo int, action string);

-- Sends a stop action on RegulatorActionStream stream, if a removed action is triggered in RoomKeyStream before the regulator state changing to off which is notified in RegulatorStateChangeStream.
INSERT INTO RegulatorActionStream
SELECT e1.roomNo,
-- Checks whether pattern triggered due to removal of room key.
    ifThenElse( e2 is null, 'none', 'stop' ) AS action
FROM every e1=RegulatorStateChangeStream[ action == 'on' ]
     -> e2=RoomKeyStream
            [ e1.roomNo == roomNo AND action == 'removed' ]
        OR e3=RegulatorStateChangeStream
            [ e1.roomNo == roomNo AND action == 'off']
HAVING action != 'none'            ;

Logical Pattern Input

• First, below event is sent to RegulatorStateChangeStream:

  [10, 5, 30, on]

• Then, send below events are sent to RoomKeyStream:

  [10, 5, removed]

Logical Pattern Output

After processing the above input events, the event arriving at RegulatorActionStream is:

[5, stop]