Event and Rule Model for ERF

1. Event and Rule Model for ERF Architecture Group ERF Project CECORD

2. Contents • Computational models of rules and events • Event model • Event examples • Rule model • Rule example • UML diagram of the rule model

3. Computational Model of Events and Rules • Events • Representation of ocurrences of interest • e.g., Raise in water level • Defined by means of classes • Each event is treated as a distributed object

4. Computational Model of Events and Rules (cont’d.) • Event set • All events are kept in a set • “Time to live” • Each event has a life time in the event set • Events might need to be alive for long periods of time • Method ts( ) – give the life time in the set, from its entrance to the set until the invocation of the method.

5. Computational Model of Events and Rules (cont’d.) • ¿When is a rule triggered ? • Each rule is triggered when the following two conditions are satisfied: • there exist enough events in the set to satisfy the event expression • e.g.A rule that needs two types of events, E1 and E2, is triggered when two events e1 (of type E1) and e2 (of type E2) enter the set • no action or alternative action has been taken by the rule for those events

6. Computational Model of Events and Rules (cont’d.) • ¿When is a rule triggered ?(cont’d.) • Event patterns • Simple • Occurrence of one event of a particular type triggers the rule • Composite events • Occurrence of varios events of different types triggers the rule if the pattern is satisfied • ¿How many times can a rule action or alternative action taken ? • Each time for each possible combination of events in the set that satisfy the event pattern

7. Computational Model of Events and Rules (cont’d.) • An event dies when: • it is removed from the set by some client of the system, or • when its time to live (ttl) expires

8. Event model (in Java) package erf; class Event extends DistributedObject { //event attributes private TimeStamp daytime; //event day-time (when it was produced) public int ttl; //time-to-live public Objectproducer; //who produced (posted) the event //event methods //constructor public Event(TimeStamp daytime, int ttl, Object producer); //return the time the event was produced public TimeStamp t( ); //return the time the event has in the event set public Integerts( ); //get the name of the class of event producer public String getProducerClass( ); //get producer object of the class DistributedObjectClass public Object getProducer( ); //return true if event is dead (time to live expired) public boolean isDead( ) //create a event public post( ); }

9. Examples of events • ************************************** • // Class GageLevelReport definition • Class GageLevelReport extends Event • { • double level; //gage water level • int loc; //gage location • } • ************************************* • ************************************** • //Class StationReport definition • Class StationReport extends Event • { • double cfs; //water flow in cubic feets per second • int loc; //station location • } • **************************************

10. Rule Model • Syntax of rule language [ package <package_spec>] rule <rule_id> [ priority <priority_no> ] on <trigger_events> [ use <usage_specification> ] [ if <condition> then <actions> [else <alt_actions>] ] [ do <actions>]

11. Rule Model (cont’d.) • Syntax of the rule language (cont’d) • <rule_id> - rule’s unique identifier • <package_spec> - package structure to which the rule belongs • <priority_no> - rule priority • <trigger_events> - event expression • <usage_specification> - distributed objects used by the rule during its execution

12. Modelo de reglas(cont.) • Syntax of the rule language (cont’d) • <condition> - conditional expression of the rule • <actions> - actions to take if the condition is true • < alt_actions> - actions to take if the condition is false

13. Rule examples • RTFAS Project (A.A.A.) package AAA rule 3-1-4 priority 5 on GageLevelReport glr1 if glr1.level >  = level value for risk alert then PosibleRiskAlert.post (glr1.loc); package AAA rule 3-5-1 on GageLevelReport glr1 >> GageLevelReport glr2 if (glr2.t( ) – glr1.t( ) <= 15) && (glr2.level – glr1.level >= 0.75) && (glr2.loc == glr1.loc) then EventInProcess.post(glr1.loc);

14. Rule examples (cont’d.) • RTFAS Project (A.A.A.) (cont’d.) package AAA rule 3-5-2 on {GageLevelReport [ (ts( ) <= 15) && ( level >= 0.50 && level <= 0.75) ] } S1 && {GageLevelReport [ ts( ) <= 15]} S2 if |S1| / |S2| > 0.5 then EventInProcess. Post( );