Skip to main content

Logical Sequences

Logical sequences identify logical relationships using and, or and not on consecutively arriving events.

Logical Sequence Syntax​

The syntax for a logical sequence is:

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>)?,
    ...

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

Example 1​

CREATE STREAM TempStream(deviceID long, temp double);
CREATE STREAM HumidStream(deviceID long, humid double);
CREATE STREAM RegulatorStream(deviceID long, isOn bool);

INSERT INTO StateNotificationStream
SELECT e2.temp, e3.humid
FROM every e1=RegulatorStream, e2=TempStream AND e3=HumidStream;

This stream worker notifies the state when a regulator event is immediately followed by both temperature and humidity events.

Example 2​

The sequence can repetitively match event sequences and use logical event ordering (using AND, OR, and NOT).

Logical Sequence Example​

This stream worker can be used identify a regulator activation event immediately followed by both temperature sensor and humidity sensor activation events in either order.

-- Defines `TempSensorStream` having information of temperature sensor device.
CREATE STREAM TempSensorStream(deviceID long, isActive bool);

-- Defines `HumidSensorStream` having information of humidity sensor device.
CREATE STREAM HumidSensorStream(deviceID long, isActive bool);

-- Defines `RegulatorStream` which contains the events from regulator with attributes `deviceID` and `isOn`.
CREATE STREAM RegulatorStream(deviceID long, isOn bool);

-- Defines `StateNotificationStream`, which logs changes.
CREATE SINK StateNotificationStream WITH (type='log') (deviceID long, tempSensorActive bool, humidSensorActive bool);


-- Identifies a regulator activation event immediately followed by both temperature sensor and humidity sensor activation events in either order.
INSERT INTO StateNotificationStream
SELECT e1.deviceID, e2.isActive AS tempSensorActive,
    e3.isActive AS humidSensorActive
FROM every e1=RegulatorStream[isOn == true],
    e2=TempSensorStream and e3=HumidSensorStream;

Logical Sequence Input​

  • First, below event is sent to RegulatorStream:

    [2134, true]

  • Then, below event is sent to HumidSensorStream:

    [124, true]

  • Then, below event is sent to TempSensorStream:

    [242, false]

Logical Sequence Output​

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

[2134, false, true]