Re: Java 8 lambdas for CEP patterns won't compile
Thank you! Hoping to see Lambda support added back in soon as well. Regards, David On Mon, Jun 12, 2017 at 1:57 PM, Kostas Kloudas wrote: > Done. > > On Jun 12, 2017, at 12:24 PM, Ted Yu wrote: > > Can you add link to this thread in the JIRA ? > > Cheers > > On Mon, Jun 12, 2017 at 3:15 AM, Kostas Kloudas < > k.klou...@data-artisans.com> wrote: > >> Unfortunately, there was no discussion as this regression came as an >> artifact of the addition of the IterativeConditions, but it will be fixed. >> >> This is the JIRA to track it: >> https://issues.apache.org/jira/browse/FLINK-6897 >> >> Kostas >> >> On Jun 12, 2017, at 11:51 AM, Ted Yu wrote: >> >> Do know which JIRA / discussion thread had the context for this decision ? >> >> I did a quick search in JIRA but only found FLINK-3681. >> >> Cheers >> >> On Mon, Jun 12, 2017 at 1:48 AM, Kostas Kloudas < >> k.klou...@data-artisans.com> wrote: >> >>> Hi David and Ted, >>> >>> The documentation is outdated. I will update it today. >>> Java8 Lambdas are NOT supported by CEP in Flink 1.3. >>> >>> Hopefully this will change soon. I will open a JIRA for this. >>> >>> Cheers, >>> Kostas >>> >>> On Jun 11, 2017, at 11:55 PM, Ted Yu wrote: >>> >>> >>> >>> >>> >> >> > >
Java 8 lambdas for CEP patterns won't compile
Hello,
I cannot get patterns expressed as lambdas like:
Pattern pattern1 = Pattern. begin("start")
.where(evt -> evt.key.length() > 0)
.next("last").where(evt -> evt.key.length() >
0).within(Time.seconds(5));
to compile with Flink 1.3.0. My IDE doesn't handle it and building on
command line with maven does not work either. The exception given by a
maven build in command line is:
[ERROR] The method where(IterativeCondition) in the type
Pattern is not applicable for the arguments (( evt)
-> {})
[ERROR]
/Users//xxx/cep-test/src/main/java/com///CEPTest.java:[83]
[ERROR] .where(evt -> evt.key.length() > 0)
[ERROR] ^^^
[ERROR] The target type of this expression must be a functional interface
I used the standard pom.xml generated by the Flink quick start archetype.
If I recall correctly this is something that used to work with Flink
1.2.0-SNAPSHOT back when I tested CEP for the first time.
Any idea why this could be the case or maybe my syntax is not correct? I
include my maven information below.
Thank you,
David
Davids-MacBook-Pro-2:cep-test dkoch$ mvn -v
Apache Maven 3.3.9 (bb52d8502b132ec0a5a3f4c09453c07478323dc5;
2015-11-10T17:41:47+01:00)
Maven home: /usr/local/Cellar/maven/3.3.9/libexec
Java version: 1.8.0_102, vendor: Oracle Corporation
Java home:
/Library/Java/JavaVirtualMachines/jdk1.8.0_102.jdk/Contents/Home/jre
Default locale: en_US, platform encoding: UTF-8
OS name: "mac os x", version: "10.11.6", arch: "x86_64", family: "mac"
Re: Listening to timed-out patterns in Flink CEP
Hello, It's been a while and I have never replied on the list. In fact, the fix committed by Till does work. Thanks! On Tue, Apr 25, 2017 at 9:37 AM, Moiz Jinia wrote: > Hey David, > Did that work for you? If yes could you share an example. I have a similar > use case - need to get notified of an event NOT occurring within a > specified > time window. > > Thanks much! > > Moiz > > > > -- > View this message in context: http://apache-flink-user-maili > ng-list-archive.2336050.n4.nabble.com/Listening-to-timed- > out-patterns-in-Flink-CEP-tp9371p12800.html > Sent from the Apache Flink User Mailing List archive. mailing list archive > at Nabble.com. >
Re: Listening to timed-out patterns in Flink CEP
Hi Till,
Excellent - I'll check out the current snapshot version! Thank you for
taking the time to look into this.
Regards,
David
On Tue, Nov 8, 2016 at 3:25 PM, Till Rohrmann wrote:
> Hi David,
>
> sorry for my late reply. I just found time to look into the problem. You
> were right with your observation that the CEP operator did not behave as
> I've described it. The problem was that the time of the underlying NFA was
> not advanced if there were no events buffered in the CEP operator when a
> new watermark arrived. This was not intended and I opened a PR [1] to fix
> this problem. I've tested the fix with your example program and it seems to
> solve the problem that you don't see timeouts after the timeout interval
> has passed. Thanks for reporting this problem and please excuse my long
> response time.
>
> Btw, I'll merge the PR this evening. So it should be included in the
> current snapshot version by the end of tomorrow.
>
> [1] https://github.com/apache/flink/pull/2771
>
> Cheers,
> Till
>
> On Fri, Oct 14, 2016 at 11:40 AM, Till Rohrmann
> wrote:
>
>> Hi guys,
>>
>> I'll try to come up with an example illustrating the behaviour over the
>> weekend.
>>
>> Cheers,
>> Till
>>
>> On Fri, Oct 14, 2016 at 11:16 AM, David Koch
>> wrote:
>>
>>> Hello,
>>>
>>> Thanks for the code Sameer. Unfortunately, it didn't solve the issue.
>>> Compared to what I did the principle is the same - make sure that the
>>> watermark advances even without events present to trigger timeouts in CEP
>>> patterns.
>>>
>>> If Till or anyone else could provide a minimal example illustrating the
>>> supposed behaviour of:
>>>
>>> [CEP] timeout will be detected when the first watermark exceeding the
>>>> timeout value is received
>>>
>>>
>>> I'd very much appreciate it.
>>>
>>> Regards,
>>>
>>> David
>>>
>>>
>>> On Wed, Oct 12, 2016 at 1:54 AM, Sameer W wrote:
>>>
>>>> Try this. Your WM's need to move forward. Also don't use System
>>>> Timestamp. Use the timestamp of the element seen as the reference as the
>>>> elements are most likely lagging the system timestamp.
>>>>
>>>> DataStream withTimestampsAndWatermarks = tuples
>>>> .assignTimestampsAndWatermarks(new
>>>> AssignerWithPeriodicWatermarks() {
>>>>
>>>> long waterMarkTmst;
>>>> long lastEmittedWM=0;
>>>> @Override
>>>> public long extractTimestamp(Event element, long
>>>> previousElementTimestamp) {
>>>> if(element.tmst>lastEmittedWM){
>>>>waterMarkTmst = element.tmst-1; //Assumes
>>>> increasing timestamps. Need to subtract 1 as more elements with same TS
>>>> might arrive
>>>> }
>>>> return element.tmst;
>>>> }
>>>>
>>>> @Override
>>>> public Watermark getCurrentWatermark() {
>>>> if(lastEmittedWM==waterMarkTmst){ //No new event seen,
>>>> move the WM forward by auto watermark interval
>>>> waterMarkTmst = waterMarkTmst + 1000l//Increase by
>>>> auto watermark interval (Watermarks only move forward in time)
>>>> }
>>>> lastEmittedWM = waterMarkTmst
>>>>
>>>> System.out.println(String.format("Watermark at %s",
>>>> new Date(waterMarkTmst)));
>>>> return new Watermark(waterMarkTmst);//Until an event
>>>> is seem WM==0 starts advancing by 1000ms until an event is seen
>>>> }
>>>> }).keyBy("key");
>>>>
>>>> On Tue, Oct 11, 2016 at 7:29 PM, David Koch
>>>> wrote:
>>>>
>>>>> Hello,
>>>>>
>>>>> I tried setting the watermark to System.currentTimeMillis() - 5000L,
>>>>> event timestamps are System.currentTimeMillis(). I do not observe the
>>>>> expected behaviour of the PatternTimeoutFunction firing once the watermark
>>>>> moves past the timeout "anchored" by a pattern match.
>>>>>
>>>>> Here is the complete test class source <http://pastebin.com/9WxGq2wv>,
>>>>>
Re: Listening to timed-out patterns in Flink CEP
Hello,
Thanks for the code Sameer. Unfortunately, it didn't solve the issue.
Compared to what I did the principle is the same - make sure that the
watermark advances even without events present to trigger timeouts in CEP
patterns.
If Till or anyone else could provide a minimal example illustrating the
supposed behaviour of:
[CEP] timeout will be detected when the first watermark exceeding the
> timeout value is received
I'd very much appreciate it.
Regards,
David
On Wed, Oct 12, 2016 at 1:54 AM, Sameer W wrote:
> Try this. Your WM's need to move forward. Also don't use System Timestamp.
> Use the timestamp of the element seen as the reference as the elements are
> most likely lagging the system timestamp.
>
> DataStream withTimestampsAndWatermarks = tuples
> .assignTimestampsAndWatermarks(new
> AssignerWithPeriodicWatermarks()
> {
>
> long waterMarkTmst;
> long lastEmittedWM=0;
> @Override
> public long extractTimestamp(Event element, long
> previousElementTimestamp) {
> if(element.tmst>lastEmittedWM){
>waterMarkTmst = element.tmst-1; //Assumes increasing
> timestamps. Need to subtract 1 as more elements with same TS might arrive
> }
> return element.tmst;
> }
>
> @Override
> public Watermark getCurrentWatermark() {
> if(lastEmittedWM==waterMarkTmst){ //No new event seen,
> move the WM forward by auto watermark interval
> waterMarkTmst = waterMarkTmst + 1000l//Increase by
> auto watermark interval (Watermarks only move forward in time)
> }
> lastEmittedWM = waterMarkTmst
>
> System.out.println(String.format("Watermark at %s", new
> Date(waterMarkTmst)));
> return new Watermark(waterMarkTmst);//Until an event is
> seem WM==0 starts advancing by 1000ms until an event is seen
> }
> }).keyBy("key");
>
> On Tue, Oct 11, 2016 at 7:29 PM, David Koch wrote:
>
>> Hello,
>>
>> I tried setting the watermark to System.currentTimeMillis() - 5000L,
>> event timestamps are System.currentTimeMillis(). I do not observe the
>> expected behaviour of the PatternTimeoutFunction firing once the watermark
>> moves past the timeout "anchored" by a pattern match.
>>
>> Here is the complete test class source <http://pastebin.com/9WxGq2wv>,
>> in case someone is interested. The timestamp/watermark assigner looks like
>> this:
>>
>> DataStream withTimestampsAndWatermarks = tuples
>> .assignTimestampsAndWatermarks(new
>> AssignerWithPeriodicWatermarks()
>> {
>>
>> long waterMarkTmst;
>>
>> @Override
>> public long extractTimestamp(Event element, long
>> previousElementTimestamp) {
>> return element.tmst;
>> }
>>
>> @Override
>> public Watermark getCurrentWatermark() {
>> waterMarkTmst = System.currentTimeMillis() - 5000L;
>> System.out.println(String.format("Watermark at %s", new
>> Date(waterMarkTmst)));
>> return new Watermark(waterMarkTmst);
>> }
>> }).keyBy("key");
>>
>> withTimestampsAndWatermarks.getExecutionConfig().setAutoWate
>> rmarkInterval(1000L);
>>
>> // Apply pattern filtering on stream.
>> PatternStream patternStream = CEP.pattern(withTimestampsAndWatermarks,
>> pattern);
>>
>> Any idea what's wrong?
>>
>> David
>>
>>
>> On Tue, Oct 11, 2016 at 10:20 PM, Sameer W wrote:
>>
>>> Assuming an element with timestamp which is later than the last emitted
>>> watermark arrives, would it just be dropped because the PatternStream does
>>> not have a max allowed lateness method? In that case it appears that CEP
>>> cannot handle late events yet out of the box.
>>>
>>> If we do want to support late events can we chain a
>>> keyBy().timeWindow().allowedLateness(x).map().assignTimestampsAndWatermarks().keyBy()
>>> again before handing it to the CEP operator. This way we may have the
>>> patterns fired multiple times but it allows an event to be late and out of
>>> order. It looks like it will work but is there a less convoluted way.
>>>
>>> Thanks,
>>> Sameer
>>>
>>> On Tue, Oct 11, 2016 at 12:17 PM, Till Rohrmann >> > wrote:
>>>
>>
Re: Listening to timed-out patterns in Flink CEP
Hello,
I tried setting the watermark to System.currentTimeMillis() - 5000L, event
timestamps are System.currentTimeMillis(). I do not observe the expected
behaviour of the PatternTimeoutFunction firing once the watermark moves
past the timeout "anchored" by a pattern match.
Here is the complete test class source <http://pastebin.com/9WxGq2wv>, in
case someone is interested. The timestamp/watermark assigner looks like
this:
DataStream withTimestampsAndWatermarks = tuples
.assignTimestampsAndWatermarks(new
AssignerWithPeriodicWatermarks() {
long waterMarkTmst;
@Override
public long extractTimestamp(Event element, long
previousElementTimestamp) {
return element.tmst;
}
@Override
public Watermark getCurrentWatermark() {
waterMarkTmst = System.currentTimeMillis() - 5000L;
System.out.println(String.format("Watermark at %s", new
Date(waterMarkTmst)));
return new Watermark(waterMarkTmst);
}
}).keyBy("key");
withTimestampsAndWatermarks.getExecutionConfig().setAutoWatermarkInterval(1000L);
// Apply pattern filtering on stream.
PatternStream patternStream =
CEP.pattern(withTimestampsAndWatermarks, pattern);
Any idea what's wrong?
David
On Tue, Oct 11, 2016 at 10:20 PM, Sameer W wrote:
> Assuming an element with timestamp which is later than the last emitted
> watermark arrives, would it just be dropped because the PatternStream does
> not have a max allowed lateness method? In that case it appears that CEP
> cannot handle late events yet out of the box.
>
> If we do want to support late events can we chain a keyBy().timeWindow().
> allowedLateness(x).map().assignTimestampsAndWatermarks().keyBy() again
> before handing it to the CEP operator. This way we may have the patterns
> fired multiple times but it allows an event to be late and out of order. It
> looks like it will work but is there a less convoluted way.
>
> Thanks,
> Sameer
>
> On Tue, Oct 11, 2016 at 12:17 PM, Till Rohrmann
> wrote:
>
>> But then no element later than the last emitted watermark must be issued
>> by the sources. If that is the case, then this solution should work.
>>
>> Cheers,
>> Till
>>
>> On Tue, Oct 11, 2016 at 4:50 PM, Sameer W wrote:
>>
>>> Hi,
>>>
>>> If you know that the events are arriving in order and a consistent lag,
>>> why not just increment the watermark time every time the
>>> getCurrentWatermark() method is invoked based on the autoWatermarkInterval
>>> (or less to be conservative).
>>>
>>> You can check if the watermark has changed since the arrival of the last
>>> event and if not increment it in the getCurrentWatermark() method.
>>> Otherwise the watermark will never increase until an element arrive and if
>>> the stream partition stalls for some reason the whole pipeline freezes.
>>>
>>> Sameer
>>>
>>>
>>> On Tue, Oct 11, 2016 at 6:04 AM, Till Rohrmann
>>> wrote:
>>>
>>>> Hi David,
>>>>
>>>> the problem is still that there is no corresponding watermark saying
>>>> that 4 seconds have now passed. With your code, watermarks will be
>>>> periodically emitted but the same watermark will be emitted until a new
>>>> element arrives which will reset the watermark. Thus, the system can never
>>>> know until this watermark is seen whether there will be an earlier event or
>>>> not. I fear that this is a fundamental problem with stream processing.
>>>>
>>>> You're right that the negation operator won't solve the problem. It
>>>> will indeed suffer from the same problem.
>>>>
>>>> Cheers,
>>>> Till
>>>>
>>>> On Sun, Oct 9, 2016 at 7:37 PM, wrote:
>>>>
>>>>> >>FLINK-3320 <https://issues.apache.org/jira/browse/FLINK-3320> (CEP
>>>>> "not" operator) does not address this because again, how would the "not
>>>>> match" be triggered if no event at all occurs?
>>>>>
>>>>> Good question.
>>>>>
>>>>> I'm not sure whether the following will work:
>>>>>
>>>>> This could be done by creating a CEP matching pattern that uses both
>>>>> of "notNext" (or "notFollowedBy") and "within" constructs. Something like
>>>>> this:
>>>>>
>>>>> Pattern pattern = Pattern.begin("first")
>>>>&g
Re: Listening to timed-out patterns in Flink CEP
I will give it a try, my current time/watermark assigner extends
AscendingTimestampExtractor so I can't override setting the watermark to
the last seen event timestamp.
Thanks for your replies.
/David
On Tue, Oct 11, 2016 at 6:17 PM, Till Rohrmann
wrote:
> But then no element later than the last emitted watermark must be issued
> by the sources. If that is the case, then this solution should work.
>
> Cheers,
> Till
>
> On Tue, Oct 11, 2016 at 4:50 PM, Sameer W wrote:
>
>> Hi,
>>
>> If you know that the events are arriving in order and a consistent lag,
>> why not just increment the watermark time every time the
>> getCurrentWatermark() method is invoked based on the autoWatermarkInterval
>> (or less to be conservative).
>>
>> You can check if the watermark has changed since the arrival of the last
>> event and if not increment it in the getCurrentWatermark() method.
>> Otherwise the watermark will never increase until an element arrive and if
>> the stream partition stalls for some reason the whole pipeline freezes.
>>
>> Sameer
>>
>>
>> On Tue, Oct 11, 2016 at 6:04 AM, Till Rohrmann
>> wrote:
>>
>>> Hi David,
>>>
>>> the problem is still that there is no corresponding watermark saying
>>> that 4 seconds have now passed. With your code, watermarks will be
>>> periodically emitted but the same watermark will be emitted until a new
>>> element arrives which will reset the watermark. Thus, the system can never
>>> know until this watermark is seen whether there will be an earlier event or
>>> not. I fear that this is a fundamental problem with stream processing.
>>>
>>> You're right that the negation operator won't solve the problem. It will
>>> indeed suffer from the same problem.
>>>
>>> Cheers,
>>> Till
>>>
>>> On Sun, Oct 9, 2016 at 7:37 PM, wrote:
>>>
>>>> >>FLINK-3320 <https://issues.apache.org/jira/browse/FLINK-3320> (CEP
>>>> "not" operator) does not address this because again, how would the "not
>>>> match" be triggered if no event at all occurs?
>>>>
>>>> Good question.
>>>>
>>>> I'm not sure whether the following will work:
>>>>
>>>> This could be done by creating a CEP matching pattern that uses both of
>>>> "notNext" (or "notFollowedBy") and "within" constructs. Something like
>>>> this:
>>>>
>>>> Pattern pattern = Pattern.begin("first")
>>>> .notNext("second")
>>>> .within(Time.seconds(3));
>>>>
>>>> I'm hoping Flink CEP experts (Till?) will comment on this.
>>>>
>>>> Note: I have requested these negation patterns to be implemented in
>>>> Flink CEP, but notNext/notFollowedBy are not yet implemented in Flink..
>>>>
>>>>
>>>> - LF
>>>>
>>>>
>>>>
>>>>
>>>> --
>>>> *From:* David Koch
>>>> *To:* user@flink.apache.org; lg...@yahoo.com
>>>> *Sent:* Sunday, October 9, 2016 5:51 AM
>>>>
>>>> *Subject:* Re: Listening to timed-out patterns in Flink CEP
>>>>
>>>> Hello,
>>>>
>>>> Thank you for the explanation as well as the link to the other post.
>>>> Interesting to learn about some of the open JIRAs.
>>>>
>>>> Indeed, I was not using event time, but processing time. However, even
>>>> when using event time I only get notified of timeouts upon subsequent
>>>> events.
>>>>
>>>> The link <http://pastebin.com/x4m3RHQz> contains an example where I
>>>> read from a socket, wrap this in a custom "event" with
>>>> timestamp, key the resultant stream by and attempt to detect
>>>> instances no further than 3 seconds apart using CEP.
>>>>
>>>> Apart from the fact that results are only printed when I close the
>>>> socket (normal?) I don't observe any change in behaviour
>>>>
>>>> So event-time/watermarks or not: SOME event has to occur for the
>>>> timeout to be triggered.
>>>>
>>>> FLINK-3320 <https://issues.apache.org/jira/browse/FLINK-3320> (CEP
>>>> "not" operator) does not address this because again, how would the "not
>>>> match" be triggered if no event at
Re: Listening to timed-out patterns in Flink CEP
Hello, Thank you for the explanation as well as the link to the other post. Interesting to learn about some of the open JIRAs. Indeed, I was not using event time, but processing time. However, even when using event time I only get notified of timeouts upon subsequent events. The link <http://pastebin.com/x4m3RHQz> contains an example where I read from a socket, wrap this in a custom "event" with timestamp, key the resultant stream by and attempt to detect instances no further than 3 seconds apart using CEP. Apart from the fact that results are only printed when I close the socket (normal?) I don't observe any change in behaviour So event-time/watermarks or not: SOME event has to occur for the timeout to be triggered. FLINK-3320 <https://issues.apache.org/jira/browse/FLINK-3320> (CEP "not" operator) does not address this because again, how would the "not match" be triggered if no event at all occurs? On Sat, Oct 8, 2016 at 12:50 AM, wrote: > The following is a better link: > > http://mail-archives.apache.org/mod_mbox/flink-user/201609.mbox/%3CCAC27z% > 3DOTtv7USYUm82bE43-DkoGfVC4UAWD6uQwwRgTsE5be8g%40mail.gmail.com%3E > > > - LF > > > > > -- > *From:* "lg...@yahoo.com" > *To:* "user@flink.apache.org" > *Sent:* Friday, October 7, 2016 3:36 PM > > *Subject:* Re: Listening to timed-out patterns in Flink CEP > > Isn't the upcoming CEP negation (absence of an event) feature solve this > issue? > > See this discussion thread: > http://mail-archives.apache.org/mod_mbox/flink-user/ > 201609.mbox/%3CCAC27z%3DOD%2BTq8twBw_1YKni5sWAU3g1S9WDpJw0DUwgiG9YX > 9Fg%40mail.gmail.com%3E > > > > // Atul > > > -- > *From:* Till Rohrmann > *To:* user@flink.apache.org > *Sent:* Friday, October 7, 2016 12:58 AM > *Subject:* Re: Listening to timed-out patterns in Flink CEP > > Hi David, > > in case of event time, the timeout will be detected when the first > watermark exceeding the timeout value is received. Thus, it depends a > little bit how you generate watermarks (e.g. periodically, watermark per > event). > > In case of processing time, the time is only updated whenever a new > element arrives. Thus, if you have an element arriving 4 seconds after > Event A, it should detect the timeout. If the next event arrives 20 seconds > later, than you won't see the timeout until then. > > In the case of processing time, we could think about registering timeout > timers for processing time. However, I would highly recommend you to use > event time, because with processing time, Flink cannot guarantee meaningful > computations, because the events might arrive out of order. > > Cheers, > Till > > On Thu, Oct 6, 2016 at 3:08 PM, David Koch wrote: > > Hello, > > With Flink CEP, is there a way to actively listen to pattern matches that > time out? I am under the impression that this is not possible. > > In my case I partition a stream containing user web navigation by "userId" > to look for sequences of Event A, followed by B within 4 seconds for each > user. > > I registered a PatternTimeoutFunction which assuming a non-match only > fires upon the first event after the specified timeout. For example, given > user X: Event A, 20 seconds later Event B (or any other type of event). > > I'd rather have a notification fire directly upon the 4 second interval > expiring since passive invalidation is not really applicable in my case. > > How, if at all can this be achieved with Flink CEP? > > Thanks, > > David > > > > > > >
Listening to timed-out patterns in Flink CEP
Hello, With Flink CEP, is there a way to actively listen to pattern matches that time out? I am under the impression that this is not possible. In my case I partition a stream containing user web navigation by "userId" to look for sequences of Event A, followed by B within 4 seconds for each user. I registered a PatternTimeoutFunction which assuming a non-match only fires upon the first event after the specified timeout. For example, given user X: Event A, 20 seconds later Event B (or any other type of event). I'd rather have a notification fire directly upon the 4 second interval expiring since passive invalidation is not really applicable in my case. How, if at all can this be achieved with Flink CEP? Thanks, David
FlinkCEP for large key spaces and long timeouts between events
Hello, Is FlinkCEP applicable to large key spaces with potentially long timeouts between events that define a pattern? Ideally, without ridiculous hardware. More concretely, we segment users (one key per user) based on sequences of events for that user. A segment "Abandoned Cart" may be defined by adding items during a browsing session but no purchase event within the following 5 days. The number of users is between 1 and 10 million. Is this type of segmentation scenario a viable use case for FlinkCEP? We currently segment by building incremental profiles in ES which are then "matched against segment definition queries" using ES percolators. In short, we incur costs when interacting with ES. Regards, David PS: Thanks for FlinkForward 2016, very interesting presentations and equally important excellent catering ;-)
