Thanks for the GSoC idea, I hope this will be a good way to improve the Siddhi language and make it more powerfull. If time permits we can also add other use-cases of patterns & sequences and improve it further.
Since you are still not a commuter I hope these contributions will help you be a committer to Siddhi as well :) I'll make this as a formal idea, do work on a proposal as well. Regards Suho On Wed, Mar 15, 2017 at 6:09 PM, Gobinath <slgobin...@gmail.com> wrote: > Hi team, > > This is Gobinath a former software engineer at WSO2 currently doing > masters at Western University. This time I plan to do GSoC with WSO2 and > this is the basic idea of what I have discussed with Suho. > Based on Suho's suggestion, I come up with a proposal to implement > detecting non-occurring events using Siddhi patterns. The current Siddhi > patterns allow identifying the patterns that present. > > See an example: > from every e1=Stream1[price>20] -> e2=Stream2[price>e1.price] within 1 sec > select e1.symbol as symbol1, e2.symbol as symbol2 > insert into OutputStream; > > Detecting the absence of a pattern is not natively supported by Siddhi > patterns for the moment. In other words, identifying event_a not followed > by event_b within 2 minutes is not possible using the current patterns > implementation (Note that a time frame is required otherwise we have to > wait for infinite time to say event_b has not arrived). The current > workaround [1] to detect non-delivered items is shown below: > > from arrivals_stream#window.time(2 minutes) > select * > insert expired events into overdue_deliveries_stream; > > from every arrivalEvent = arrivals_stream -> > deliveryEvent = deliveries_stream[arrivalEvent.trackingId == trackingId] > or overdue_delivery = overdue_deliveries_stream[arrivalEvent.trackingId > == trackingId] > select arrivalEvent.trackingId as trackingId, arrivalEvent.customerName as > customerName, arrivalEvent.telephoneNo as telephoneNo, > deliveryEvent.trackingId as deliveryId > insert into filter_stream; > > from filter_stream [ (deliveryId is null)] > select trackingId, customerName, telephoneNo > insert into alert_stream; > > This solution requires a time window and it is inefficient if we are > interested only on one occurrence of such a pattern (In other words same > query without every keyword). Further, the query is more complex and not > user-friendly. > > If we provide patterns to detect absence of patterns, the above query can > be rewritten as below: > > from every arrivalEvent = arrivals_stream -> (not > deliveries_stream[arrivalEvent.trackingId == trackingId] within 2 min ) > select arrivalEvent.trackingId as trackingId, arrivalEvent.customerName as > customerName, arrivalEvent.telephoneNo as telephoneNo > insert into alert_stream; > > As you can see, we can use the existing language components like not & > within. This can be achieved by extending the existing > StreamPreStateProcessors and StreamPostStateProcessors with an internal > timer so that they can expire their internal list of events based on the > time limit. It is somewhat similar to time windows but the processor can > turn off the timer and ignore the events if it is a one time pattern > detection. > > I hope it gives the basic idea and I am waiting for your suggestions and > feedback. > > [1] https://docs.wso2.com/display/CEP400/Sample+0111+-+D > etecting+non-occurrences+with+Patterns > > > Thanks & Regards, > Gobinath > -- > *Gobinath** Loganathan* > Graduate Student, > Electrical and Computer Engineering, > Western University. > Email : slgobin...@gmail.com > Mobile : (+1) 416-895-0721 > Blog : javahelps.com <http://www.javahelps.com/> > > -- *S. Suhothayan* Associate Director / Architect & Team Lead of WSO2 Complex Event Processor *WSO2 Inc. *http://wso2.com * <http://wso2.com/>* lean . enterprise . middleware *cell: (+94) 779 756 757 | blog: http://suhothayan.blogspot.com/ <http://suhothayan.blogspot.com/>twitter: http://twitter.com/suhothayan <http://twitter.com/suhothayan> | linked-in: http://lk.linkedin.com/in/suhothayan <http://lk.linkedin.com/in/suhothayan>*
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