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From Anwar Rizal <anriza...@gmail.com>
Subject Re: CEP API: Question on FollowedBy
Date Tue, 05 Apr 2016 11:07:44 GMT
Thanks Till.

The only way I can change the behavior would be to post filter the result
then.

Anwar.

On Tue, Apr 5, 2016 at 11:41 AM, Till Rohrmann <trohrmann@apache.org> wrote:

> Hi Anwar,
>
> yes, once we have published the introductory blog post about the CEP
> library, we will also publish a more in-depth description of the approach
> we have implemented. To spoil it a little bit: We have mainly followed the
> paper “Efficient Pattern Matching over Event Streams” for the
> implementation.
>
> Concerning your questions:
>
> 1.) followedBy means that there can be an arbitrary sequence of events
> between two matching events, as long as they occur in the specified time
> interval. Thus, TemperatureEvent(40) will match together with
> TemperaturEvent(50), TemperaturEvent(70), TemperaturEvent(65) and
> TemperaturEvent(60).
>
> 2.) The same applies here for the next operator. It says that the second
> matching event has to follow directly after the previous matched event.
> However, a matching event can be part of multiple matching sequences. Thus,
> you will get TemperaturEvent(70), TemperaturEvent(65) and
> TemperaturEvent(65), TemperaturEvent(60) as two distinct matching sequences.
>
> To make a long story short, there is currently no option to change the
> sequence semantics so that events are only part of one matching sequence.
> At the moment, events can participate in multiple matching sequences. I
> hope that answers your question Anwar.
>
> Cheers,
> Till
> ​
>
> On Mon, Apr 4, 2016 at 11:18 AM, Anwar Rizal <anrizal05@gmail.com> wrote:
>
>> Hi All,
>>
>>
>> I saw Till's blog preparation. It will be a very helpful blog. I hope
>> that some other blogs that explain how it works will come soon :-)
>>
>> I have a question on followedBy pattern matching semantic.
>>
>>
>> From the documentation
>> https://ci.apache.org/projects/flink/flink-docs-master/apis/streaming/libs/cep.html
>> ,
>>
>> <citaton>
>>
>> Non-strict contiguity means that other events are allowed to occur
>> in-between two matching events. A non-strict contiguity pattern state can
>> be created via the followedBy method.
>>
>> Pattern<Event, ?> nonStrictNext = start.followedBy("middle");
>>
>>
>> </citation>
>>
>> I try to use Till's examples in the blog, to understand the semantic of
>> followedBy
>>
>> --
>> First question.
>> Say, I have sequence of temperatures in a time window that corresponds to
>> the within clause (say in 20 minutes).
>>
>> TemperatureEvent(40) , OtherEvent(...), TemperatureEvent(30),
>> TemperatureEvent(50), OtherEvent(...), TemperatureEvent(70),
>> TemperatureEvent(65), TemperatureEvent(60)
>>
>> say I want to match two TemperatureEvents whose temperatures > 35.
>>
>> What will be the matches in this case ?
>>
>>
>>    -  Will TemperatureEvent(40) , TemperatureEvent(50), match ? (because
>>    we have TemperatureEvent(30) at time 3 that does not match.
>>    - Will TemperatureEvent(40) , TemperatureEvent(70) match ? (because
>>    the pair matches also the specification of pattern , the difference is we
>>    have TemperatureEvent(50) which happened before TempertureEvent(70) ).
>>    Similar question for TemperatureEvent(40) - TemperatureEvent(65) and
>>    TemperatureEvent(50)-TemperatureEvent(65) etc. pairs.
>>
>>
>>
>> --
>> Second question.
>> For next (and also for followedBy) , I have also questions regarding
>> example above:
>> Will TemperatureEvent(70), TemperatureEvent(65) and TemperatureEvent(65),
>> TemperatureEvent(60) be returned , or the second pair is no longer returned
>> because TemperatureEvent(65) has been used in the first pair ?
>>
>>
>>
>> Is there a way to define the different sequence semantics  for the two
>> questions I asked above ?
>>
>>
>> Thanks,
>> Anwar.
>>
>>
>>
>>
>>
>>
>>
>>
>
>

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