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Date: Wed, 26 Jul 2017 09:05:01 +0000 (UTC)
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Subject: [jira] [Commented] (FLINK-7169) Support AFTER MATCH SKIP function
 in CEP library API
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archived-at: Wed, 26 Jul 2017 09:05:15 -0000


    [ https://issues.apache.org/jira/browse/FLINK-7169?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16101390#comment-16101390 ] 

ASF GitHub Bot commented on FLINK-7169:
---------------------------------------

Github user yestinchen commented on a diff in the pull request:

    https://github.com/apache/flink/pull/4331#discussion_r129518272
  
    --- Diff: flink-libraries/flink-cep/src/main/java/org/apache/flink/cep/nfa/NFA.java ---
    @@ -551,18 +579,47 @@ private boolean isSelfIgnore(final StateTransition<T> edge) {
     								nextVersion,
     								startTimestamp);
     					}
    +
    +					switch (skipStrategy.getStrategy()) {
    +						case SKIP_PAST_LAST_ROW:
    +							if (nextState.isFinal()) {
    +								resultingComputationStates.add(createStartComputationState(computationState, outgoingEdges));
    +							}
    +							break;
    +						case SKIP_TO_FIRST:
    +							if (nextState.getName().equals(skipStrategy.getRpv()) &&
    +								!nextState.getName().equals(currentState.getName())) {
    +								ComputationState<T> startComputationState = createStartComputationState(computationState, outgoingEdges);
    --- End diff --
    
    Now I keep `startComputationState` instead of `startState` in NFA, so it can calculate the `outgoingEdges` from the start state when needed. Is this right? 


> Support AFTER MATCH SKIP function in CEP library API
> ----------------------------------------------------
>
>                 Key: FLINK-7169
>                 URL: https://issues.apache.org/jira/browse/FLINK-7169
>             Project: Flink
>          Issue Type: Sub-task
>          Components: CEP
>            Reporter: Yueting Chen
>            Assignee: Yueting Chen
>
> In order to support Oracle's MATCH_RECOGNIZE on top of the CEP library, we need to support AFTER MATCH SKIP function in CEP API.
> There're four options in AFTER MATCH SKIP, listed as follows:
> 1. AFTER MATCH SKIP TO NEXT ROW: resume pattern matching at the row after the first row of the current match.
> 2. AFTER MATCH SKIP PAST LAST ROW: resume pattern matching at the next row after the last row of the current match.
> 3. AFTER MATCH SKIP TO FIST *RPV*: resume pattern matching at the first row that is mapped to the row pattern variable RPV.
> 4. AFTER MATCH SKIP TO LAST *RPV*: resume pattern matching at the last row that is mapped to the row pattern variable RPV.
> I think we can introduce a new function to `CEP` class, which takes a new parameter as AfterMatchSKipStrategy.
> The new API may looks like this
> {code}
> public static <T> PatternStream<T> pattern(DataStream<T> input, Pattern<T, ?> pattern, AfterMatchSkipStrategy afterMatchSkipStrategy) 
> {code}
> We can also make `SKIP TO NEXT ROW` as the default option, because that's what CEP library behaves currently.


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