12:25 p.m.
Michael Neale wrote:
Hi Edson.
My $0.02 AUD:
1. I choose time-window( 30 min )
we have two different types of windows - time
and length. The above
means each window would be a fixed separate keyword. Where as "win" and
then a sub-unit would would indicate the type of window. "-" does not
really indicate a sub unit, where as : and . do.
2. I choose option 2: eg TemperatureReading( window-events(60),
window:time(1 min), temp > 50 ) from streamB
I think it would be a mistake to
mix keywords and field constraints so
freely in an almost similar syntax. I think there needs to be a clearer
distinction between what is a behaviour attribute on a pattern and what
is a field constraint. behaviour attributes work on sets/groups of
objects, field constraints work on individual objects.
3. I choose distinct Address() from $person.address
(I guess lexically speaking, its similar to exists, not, etc).
We didn't want
ot make distinct a keyword, as their may be other user
implementations. For this reasn we wanted it to be a text glob the
parser can suck in and the factory creates the required implementation.
This is part of the reason for the need for delimeters, this extra
pluggabiilty/flexability ofcourse has a cost in removing the english
like qualities.
The other option is we have a fxed and non user-extensible grammar, we
are still not sure on the likelyhood for the on alternatives to distinct
- although I can think of one other "last". In banking if you have a
stream of data come in you want the last entry for a given ticker type.
So distinct,last etc are simply ways to massage groups of values for
that window.
On Nov 28, 2007 12:08 PM, Edson Tirelli <tirelli(a)post.com
<mailto:tirelli@post.com>> wrote:
Resending...
---------- Forwarded message ----------
Karen and Matthias,
Thanks for the suggestions. A few items that we need to solve
before we decide on a syntax:
1. The qualification of the units: we need to be able (as a CEP
engine) to allow the definition of arbitrary time windows, like
seconds, minutes or hours or compositions of them. So, a few
notations could be used: 30 sec, 30 min, 30 hours (or variations
of that), 25:10:23 (25 hours and 10 minutes and 23 seconds), etc.
I would really like to avoid hard coding the unit parsing in the
DRL parser, since the parser is one of the more delicate pieces of
the code to change. We can avoid that if we use delimiters to
declare t mulhe "parameters" of the window, as the parser can
simply read it all as a String chunk and let each window handler
deal with its own units. So, the suggestion is to use () or
something like that to provide the parameters to the window
handlers, in a way like that:
window:time( 30 min ) or time-window( 30 min ) or another
variation of that
window:events( 60 ) or events-window( 60 ) or another variation of
that
2. The smallest "unit" in a rule definition is a Pattern, and
right now, a Pattern looks like this:
[<var-bind> : ] <Pattern-Type>( [<constraints>] ) [from
<source>]
<> : means must be replaced by the corresponding data
[] : means optional
Now, what we need is a way to declare window constraints for
patterns. The accumulate example I gave you was not a good one,
because accumulates have 2 or more patterns (the inner patterns
and the accumulate result pattern). You can even apply different
window constraints for each of the patterns.
So, thinking about a single pattern, how would you define a window
for it?
Given the current grammar and the concept of pattern, I see only
two options: either we define the window constraints inside the
pattern declaration ( i.e., near regular constraints), or we
create another keyword to introduce them (like we have the "from"
keyword).
option 1: [<var-bind> : ] <Pattern-Type>( [<window-constraints> ,]
[<constraints>] ) [from <source>]
option 2: [<var-bind> : ] <Pattern-Type>( [<constraints>] ) [from
<source>] [with <window-constraints>]
Note: replace the "with" above with the keyword we chose.
Just as a real world example, if you look at ESPER queries, they
do events correlation like this:
select *
from TxnEventA.win:time(30 minutes) A
join TxnEventC.win:time(60 minutes) C on A.transactionId = C.transactionId
join TxnEventB.win:time(30 minutes) B on B.transactionId =
C.transactionId
where C.transactionId is null
One example of event aggregation is this:
select min(latencyAC) as minLatencyAC, max(latencyAC) as maxLatencyAC, avg(latencyAC)
as avgLatencyAC
from CombinedEvent.win:time
(30 minutes)
So, you see that the time windows are defined for each pattern and
they may be different among joined patterns.
Accumulate may have multiple inner patterns, and so, we need to be
able to define windows for each one.
On our initial suggestions, we would define the window constraints
inside the pattern, as this is a lot better to avoid grammar
ambiguities. The use of square brackets would help to avoid the
need of creating new keywords, but as long as we decide that it is
worth to create at least one keyword (like "window" for instance),
we can avoid the []:
TemperatureReading( window:time(30 sec), temp > 50 ) from streamA
TemperatureReading( window:events(60), window:time(1 min), temp >
50 ) from streamB
Something closer to what you suggested would be (replace "with"
with a chosen keyword) :
TemperatureReading( temp > 50 ) from streamB with
window:events(60), window:time(1 min)
My preference is to keep that inside the pattern, but would like
to hear from you (if the change proposed in item #1 is ok) and
from Mark and Michael.
3. Regarding "distinct", "group by" and "order by", we
want to
support that, specially "distinct". From a syntax perspective, I
would like to use a similar solution as we chose for the windows,
so that we can keep the language easier to learn, but if it is
best for clarity to use them like "distinct PatternA(...)", I'm ok
with that too. Unfortunately, we can't allow distinct directly for
attributes, as different from SQL, we need to declare all the
patterns that make a tuple. So, instead of saying something like:
Person( distinct address )
we need to say something like:
distinct Address() from $person.address
Address( distinct ) from $person.address
Anyway, item #3 is of minor importance right now.
Sorry for the long e-mail.
Edson
2007/11/27, kw14(a)mail.inf.tu-dresden.de
<mailto:kw14@mail.inf.tu-dresden.de> <kw14(a)mail.inf.tu-dresden.de
<mailto:kw14@mail.inf.tu-dresden.de>>:
Hi Mark, hi Edson,
in the following you'll find our suggestions regarding Drools
syntax
extensions for definition of windows and other node restrictions.
Edson showed us an example of what you had in mind:
Number( avg : doubleValue ) from accumulate( TemperatureReading( [
window:events( 30 ), window:time( 60 sec ), distinct ], $temp :
temperature ), average( $temp ) )
It calculates the average of distinct temperature readings in
60 seconds
or over 30 events (whatever comes first).
Your notation has the advantage of being short, easy to use
and orthogonal
to the current grammar.
In contrast to the definition using square brackets, we'd
prefer a more
explicit way of defining windows and other constraints. This
increases
readability and makes it easier for novices to define rules.
You've also
used a similar notation in your talk at Synasc 2007.
So our version would look like this:
Number( avg : doubleValue ) from accumulate within|in|over 60s
or 30
events( distinct TemperatureReading($temp : temperature ),
average( $temp
))
It allows using nested 'accumulates' while its clear to which
'accumulate'
a window definition belongs. The usage of "in", "within" or
"over" as a
keyword is up to your preference. The "distinct" keyword could
be used in
front of either an object or an attribute definition similar
to select
"distinct *" vs. "select distinct fieldname" in SQL. We
think
it's clearer
to have it in front of the object/attribute it refers to.
For collect, a definition would look similar:
e.g .
ArrayList( ) from collect over 60s ( TemperatureReading( orderBy
temperature > 0 , distinct id!=null ) )
In this case, we also used an "orderBy" keyword similar to
distinct.
However, it could also be used like a function as is currently
done with
aggregation functions in 'accumulate':
ArrayList( ) from collect over 60s ( TemperatureReading(
$temp:temperature
> 0 , distinct id!=null ), orderBy($temp) )
For us, orderBy and groupBy only make sense with the set operator
'collect'. Although, they could be used in 'accumulate', if
the order of
values is relevant to the result of a user-defined aggregation
function or
if different result sets are created based on a grouping
attribute. Are
you planning to support this?
Window definitions can also make sense for the 'exists' and
'not'
operators or a complete rule as already suggested by Edson.
An alternative way of describing the windows and other
constructs would be
the one below. However, it would require additional brackets
to show the
scope of windows for nested accumulates and was therefore
excluded from
our considerations.
Number( avg : doubleValue ) from accumulate( distinct
TemperatureReading($temp : temperature ), average( $temp ) )
over 60s or
30 events
Okay, we are aware that these suggestions would require more
extensions in
the Drools grammar, but we believe the resulting rules are
easier to
understand than the ones using the square brackets. So, that's
open for
discussion. :)
Cheers, Karen
--
Edson Tirelli
JBoss Drools Core Development
Office: +55 11 3529-6000
Mobile: +55 11 9287-5646
JBoss, a division of Red Hat @ www.jboss.com <http://www.jboss.com>
--
Edson Tirelli
JBoss Drools Core Development
Office: +55 11 3529-6000
Mobile: +55 11 9287-5646
JBoss, a division of Red Hat @ www.jboss.com <http://www.jboss.com>
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--
Michael D Neale
home: www.michaelneale.net <http://www.michaelneale.net>
blog: michaelneale.blogspot.com <http://michaelneale.blogspot.com>
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