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From: dawidwys <git@git.apache.org>
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References: <git-pr-4296-flink@git.apache.org>
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Subject: [GitHub] flink issue #4296: [FLINK-7147] [cep] Support greedy quantifier in CEP
Content-Type: text/plain
Message-Id: <20170807113628.47EC9E10F8@git1-us-west.apache.org>
Date: Mon,  7 Aug 2017 11:36:27 +0000 (UTC)
archived-at: Mon, 07 Aug 2017 11:36:38 -0000

Github user dawidwys commented on the issue:

    https://github.com/apache/flink/pull/4296
  
    There is also one more problem. When we have optional after `greedy` it does not work well. E.g. have a look at this test case:
    
    	@Test
    	public void testGreedyZeroOrMoreBeforeOptional2() {
    		List<StreamRecord<Event>> inputEvents = new ArrayList<>();
    
    		Event c = new Event(40, "c", 1.0);
    		Event a1 = new Event(41, "a", 2.0);
    		Event a2 = new Event(42, "a", 2.0);
    		Event d = new Event(43, "d", 3.0);
    		Event a3 = new Event(42, "a", 2.0);
    		Event e = new Event(44, "e", 3.0);
    
    		inputEvents.add(new StreamRecord<>(c, 1));
    		inputEvents.add(new StreamRecord<>(a1, 2));
    		inputEvents.add(new StreamRecord<>(a2, 3));
    		inputEvents.add(new StreamRecord<>(d, 4));
    		inputEvents.add(new StreamRecord<>(a3, 5));
    		inputEvents.add(new StreamRecord<>(e, 6));
    
    		// c a* d e
    		Pattern<Event, ?> pattern = Pattern.<Event>begin("start").where(new SimpleCondition<Event>() {
    			private static final long serialVersionUID = 5726188262756267490L;
    
    			@Override
    			public boolean filter(Event value) throws Exception {
    				return value.getName().equals("c");
    			}
    		}).followedBy("middle1").where(new SimpleCondition<Event>() {
    			private static final long serialVersionUID = 5726188262756267490L;
    
    			@Override
    			public boolean filter(Event value) throws Exception {
    				return value.getName().equals("a");
    			}
    		}).oneOrMore().optional().greedy().followedBy("middle2").where(new SimpleCondition<Event>() {
    			private static final long serialVersionUID = 5726188262756267490L;
    
    			@Override
    			public boolean filter(Event value) throws Exception {
    				return value.getName().equals("d");
    			}
    		}).optional().followedBy("end").where(new SimpleCondition<Event>() {
    			private static final long serialVersionUID = 5726188262756267490L;
    
    			@Override
    			public boolean filter(Event value) throws Exception {
    				return value.getName().equals("e");
    			}
    		});
    
    		NFA<Event> nfa = NFACompiler.compile(pattern, Event.createTypeSerializer(), false);
    
    		final List<List<Event>> resultingPatterns = feedNFA(inputEvents, nfa);
    
    		compareMaps(resultingPatterns, Lists.<List<Event>>newArrayList(
    			Lists.newArrayList(c, a1, a2, a3, e),
    			Lists.newArrayList(c, a1, a2, d, e)
    		));
    	}
    
    Right know it also returns `c a1 a2 e`, which I think is not correct. I don't think there is an easy way to fix it right now. I would suggest restricting on the Pattern level that greedy must not be followed by an `Optional` patten. I would like to hear opinions on that, @kl0u.


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