About the Use of Correlations in Component Based Frameworks

Georg Jungjung@cis.ksu.edu

Department of Computing and Information Sciences

Kansas State University

b

Why Using Correlators?

Component C is receiving from two components A and B

A and B send at different rates

C needs both inputs to become active

Consider the following situation:

aA

B

Cab

b

Why Using Correlators!

We can: Reduce network

traffic Simplify computation

inside the component Clarify the design Define the

components in a more general way

Consider the following situation:

a

ab C

A

B

a + b

If we addcorrelations to

the infrastructure

Hello World!Scenario:Example scenario from introduction slides:

C

A

B

• Three Components A, B, and C • Component C receives • A and B send at different rates

TransformerFilter

Head

Hello World!φC correlation HelloWorld (φA a, φB b)a + b

{case true:push new φC { x := a.data,

y := b.data }}

Information about: which events arrived what data is present

The Two-Phase ModelConceptually, the correlator divides

into two distinct phases:1. The Filter2. The Transformere1 e3 e1 e2 e2

Stream of incoming events

Filter

Transformereout eout

Information about: which events arrived what data is present

Generates new output events

Detection ofevent patterns

Reacting to adetected pattern

And performs internal actions

Transformer

Filter

φC correlation HelloWorld (φA a, φB b)a + b

{case true:push new φC { x := a.data,

y := b.data }}

Back to “Hello World!”

In this simple examplethe transformer does

a type conversion!

ExamplesThis presentation will include: How to prevent a race condition How to chose the most recent/earliest in a

sequence How to handle a double match How to catch interleaving events How to deal with redundant-device-

components How to introduce mode-dependent behavior How to bridge the gap between periodic and

aperiodic systems

Race ConditionScenario:Components A and B carry out a task

and deliver the results to C.Component C expects the results to

come in first from A, then from B.

The resulting race condition betweenA and C can be caught with a

correlator.

Race ConditionSolution:φdata correlation CatchRacing (φdata a, φdata b)

a + b{

case true:push a;push b;

}

ExamplesThis presentation will include: How to prevent a race condition How to chose the most recent/earliest in a

sequence How to handle a double match How to catch interleaving events How to deal with redundant-device-

components How to introduce mode-dependent behavior How to bridge the gap between periodic and

aperiodic systems

Most Recent / EarliestScenario:A component C receives from A and B.

a + bwhen both events arrive, C wants the

most recent (earliest) of both forwarded.

We change the filter expression to:la:(a ; b) | lb:(b ; a)

Most Recent / EarliestφData correlation First

(φData a; φData b)la:(a; b) | lb:(b; a)

{case la: push a;case lb: push b;

}

ExamplesThis presentation will include: How to prevent a race condition How to chose the most recent/earliest in a

sequence How to handle a double match How to catch interleaving events How to deal with redundant-device-

components How to introduce mode-dependent behavior How to bridge the gap between periodic and

aperiodic systems

Double MatchConsider the following filter expression:

(a + b) | (a + c)

And the following streams:

a b a a c c …

a c a b b a …

c b b c a a …

matches: a + bmatches: a + cmatches: a + band a + c

Double Match

(a + b) | (a + c)

l1:(a + b) | l2:(a + c)

Adding Labels to the expression

Double Matchl1:(a + b) | l2:(a + c)

Transformer 1: Send a general notification

{case true: push new φnote {};

}

Double Matchl1:(a + b) | l2:(a + c)

Transformer 2: Send two outputs

{case l1: push b;case l2: push c;

}

Double Matchl1:(a + b) | l2:(a + c)

Transformer 3: Send one output, withpriority on b if present.

{case l1: push b;case l2 & !l1: push c;

}

ExamplesThis presentation will include: How to prevent a race condition How to chose the most recent/earliest in a

sequence How to handle a double match How to catch interleaving events How to deal with redundant-device-

components How to introduce mode-dependent behavior How to bridge the gap between periodic and

aperiodic systems

Interleaving EventWe consider three subexpressions x1, x2, x3. x2 shall not interleave between x1 and x3.

x1 ; (l2:(x2 ; x3) | l3:x3)

φ correlation Interleaving (...)x1 ; (l2:(x2 ; x3) | l3:x3)

{case l2: push some error event;case l3 & !l2: push some success event;

}

ExamplesThis presentation will include: How to prevent a race condition How to chose the most recent/earliest in a

sequence How to handle a double match How to catch interleaving events How to deal with redundant-device-

components How to introduce mode-dependent behavior How to bridge the gap between periodic and

aperiodic systems

Redundant-Sensor-ArrayConsider an array of redundant components

A1, A2, …, An.and a single receiving component B, interested in the accumulation of all events

a1, a2, …, an.The filter expression is then

a1 + a2 + … + an

An

A3A2

…

A1 +B

Redundant-Sensor-Arraya1 + a2 + … + an

In a component system some components

can be temporarily unavailable!If one component does not send anymore

the whole pattern is never satisfied!

An

A3A2

…

A1 +B

An

A3A2

…

A1

Redundant-Sensor-ArrayNotify correlation SensorArray (Notify a1, …, Notify an, Control c1, …, Control cn)l1:a1 + … + ln:an || m1:c1 || … || mn:cn

{ case l1 & … & ln: push new Notify {} case m1: toggle l1 …case mn: toggle ln

}

Sensor

Array

B

C

ExamplesThis presentation will include: How to prevent a race condition How to chose the most recent/earliest in a

sequence How to handle a double match How to catch interleaving events How to deal with redundant-device-

components How to introduce mode-dependent behavior How to bridge the gap between periodic and

aperiodic systems

Mode-AwarenessScenario:This scenario generalizes the previous.

Instead of single devices to switch on or off, we have a several modes to chose from.The same mechanism is used

to switch between modesas previously to switch the

different devices on and off.

Mode Awarenessn filter expressions, labeled with n

labels:m1:e1 || … || mn:en

n labeled control events:l1:c1 || … || ln:cn

Mode Awarenessφout correlation Modal3(φc c1, φ c c2, φ c c3, arguments for ei…)m1: e1 || m2: e2 || m3: e3 ||l1: c1 || l2: c2 || l3: c3

{abort (m2, m3);

clauses for e1, e2, e3…

case l1: revive (m1); abort (m2, m3);case l2: revive (m2); abort (m1, m3);case l3: revive (m3); abort (m1, m2);

}

ExamplesThis presentation will include: How to prevent a race condition How to chose the most recent/earliest in a

sequence How to handle a double match How to catch interleaving events How to deal with redundant-device-

components How to introduce mode-dependent behavior How to bridge the gap between periodic and

aperiodic systems

Periodic Checks of Aperiodic EventsScenario:We introduce a periodic supervisor

component into an aperiodic system.

Whenever a clock-tick occurs, a sample is collected and sent to the supervisor.

φsample correlation PeriodicChck(φtimer t, φa a, φb b, φc c)t ; (l1:(a + b + c) | l2:t)

{case l1:push new φsample{d1 := a.data,d2 := b.data,

d3 := c.data }case l2:push some error event (missed sample);

}

Periodic Checks of Aperiodic Events

ExamplesThis presentation will include: How to prevent a race condition How to chose the most recent/earliest in a

sequence How to handle a double match How to catch interleaving events How to deal with redundant-device-

components How to introduce mode-dependent behavior How to bridge the gap between periodic and

aperiodic systems

These are our examples.Feel free to add your own…