What is an edge in event processing network ? - a terminology wondering

Today I'll leave the macro questions about SOA and positioning of event processing discipline, and deal with a micro issue, an issue of terminology, that came up when I have looked at the current draft of the event processing glossary is the following issue: one of the main abstractions of event processing is event processing network. The network is in essence a directed (maybe cyclic) graph, as any graph it consists of nodes and edges, the definition in the glossary is: Event Processing Network (EPN): A set of event processing agents (EPAs) and a set of event channels connecting them. Clearly, EPA is a node - one can also say that producers and consumer are type of nodes (to show the entire picture), the question is what is an edge in this network -- from the definition one may assume that channel is an edge, however unlike an edge in graph, that connect two nodes, a channel may have multiple sources and multiple sinks, thus it is more comfortable to look at the channel as another type of node (and indeed channel has also some functions associated with it), thus channel is not the edge, we can say is that edge is the "pipe" through which a events flow from one node (producer, channel, agent) to another node (channel, agent, consumer). Now we need to determine what it is ? my suggestion is to call such a collection an "event stream", however, the glossary defines it as:
Event stream: a linearly ordered sequence of events. Here we have two issues - one to distinguish between the "pipe" and the collection of events flowing on this "pipe", which is the same type of ambiguity we have when talking about "event" vs. "event message", however, we can tolerate such ambiguity, the second problem is in general the collection of such events may not be totally ordered, thus it does not conform with the definition of stream.

There are two possible solutions --- one to modify the definition of stream to be more general (I am not sure that the word stream inherently mean sequence, it is just happened to be the way it was implemented in a certain academic project), the other possibility is to invent a new name for the edge - like event pipe (or some other creative name). What do you think ?

I am also putting it as a comment on the glossary website.

I am taking this opportunity to suggest that anybody who wishes to make a terminology comment will do it soon, since we would like to close a first version in the next month or so.

More terminology issues - later.

Event Processing - a footnote to databases ?

More in the spirit of the VLDB conference I've attended last week, there is a conception in the database community that event processing is really part of database technology, and that the functionality of event processing can be obtained using regular databases by inserting the events into the database, and asking "continuous queries" in the database. According to this outlook, the only reason that customers want to have engines outside the database engine is when some performance properties - typically - throughput and latency cannot be satisfied by database engines, but this can be handled by some tricks - like in-memory databases.


This reminds me that in the first conference I have ever organized: NGITS 1993 (we did not have conference webpages at those days) there was a discussion about the relations between Artificial Intelligence and Databases that followed the keynote address of John Mylopoulos, whom I always considered as one of the most visionary people I've ever met, John said something like this "the difference between AI and database discipline is that AI is a scientific discipline and database is an engineering discipline, which deals of efficiency issues", he, of course, made the database people who were present, quite angry, however, now that I am looking from the outside (at that time I have looked from the inside) on the way that database people think, I realize that he was, as usual, right.


While, high performance is one of the reasons that customers turn to COTS in this area, this is only the secondary reason, the main reason is that event processing software is being used is the level of abstraction they provide, and consequently the improvement in ROI. It seems also that the main competition between different products will be more in the ROI (ease of use) front, then in the performance front.


Event processing is different in the required functionality from database processing, the fact that database processing processes a state ("snapshot"), and event processing processes a set of transitions ("event cloud") impose different thinking, and hence different abstractions. Trying to introduce event pattern detection as extension to database processing (as we have seen in the EPTS meeting, the proposal being prepared now) have several attributes - simplicity is not part of them, and thus it totally misses the point of "ease of use", only to satisfy the assertion that event processing should be done within database processing. While these are nice academic attempts, and probably researchers will be able to write a lot of papers about the pattern extensions to SQL, I don't believe that they will catch in reality.


However - databases do have several roles in event processing, here are a few of them:

(1). Databases will be used to store events that should be used for retrospective processing. These database require to support temporal (or even spatio-temporal) characteristics; the database products don't provide yet good support of this area, and this deserves a separate blog.

(2). Databases (or in-memory databases) Will be used to store intermediate states for recoverability.

(3). Databases will be used to enrich events for processing (mainly reference data, but sometimes transaction data).
(4). Data warehouses will be used for embedded analytics.

I think that the database community should concentrate in enhancing database technology to support these functions in event processing -- e.g. temporal database support - both in abstraction level and efficiency in implementation, instead of insist on extend SQL in unnatural way.

I still need to discuss in more depth several topics like: temporal databases, retrospective processing, and alternative approach for SQL patterns, but will leave it for later.

The trap of ambiguity - case of "event correlation"

One of the terms that is missing from the event processing glossary is "event correlation", yet, I don't miss this term at all, in facts, I am trying to lose it for years. The main reason is the homonym effect which the same term is used in different meaning. Here is the collection of different meanings that I know of of this term:

1. A network and system management application: following the ComputerWorld article - "Event correlation simplifies and speeds the monitoring of network events by consolidating alerts and error logs into a short, easy-to-understand package" - in this case the idea is to reduce the number of symptoms and concentrate on problems.

2. Some call the pattern detection part of CEP in the name "event correlation"

3. Some call the matching between events and data (e.g. for enrichment) as "event correlation"

4. Some are using the "correlation identifier pattern" in the enterprise integration patterns - the act of matching two events based on shared attributes.

5. Last but not least, event correlation refers to statistical correlation among the occurrence of two events, used to mine patterns of causalities.

So - what is the problem in homonyms ? the problem is that since in general there is a confusion of terms in this area, homonyms tend to intensify the confusion, especially among decision makers who don't really have technical depth, but get decision based on perceived impressions -- this may have undesired results.

Thus, I prefer to use non-ambiguous terms as much as possible, and avoid confusing slang.

This is just one example of confusing terminology, in a recent incident I noticed people spending much energy trying to understand what is the meaning of BAM (which I may discuss in another time).... The consensus glossary is not just a "nice to have", it is a business tool to save a lot of time on miscommunication.... More, later.

More on EDA is EDA and SOA is SOA

Hello from Haifa again. My good friend Tim Bass has written a blog entitle EDA is EDA and SOA is SOA. I totally agree that EDA and SOA are not the same, more than that, I don't even think that they are talking about the same thing. Many people equate SOA with the synchronous "request-reply" style of interaction, but this is only one way to implement SOA, since SOA is not about interaction style, but about modularization or componentization of the enterprise, and hence it IT systems, introducing them as "services", the interaction style is a secondary issue, services can interact both in synchronous and asynchronous ways, and there is nothing inherent in the concept of services that say anything about the interaction type. EDA is indeed about asynchronous push interaction style, and this can be interaction between services, where we get both SOA and EDA, or interaction between other software artifacts, in enterprises that don't implement SOA. Implementation of SOA and EDA both make sense for other reasons and to solve other problems, and they are completely orthogonal. In enterprises that implement SOA there is a sense to use a combination of both, thus, it is important to position them in a way that they are complementary and not contradictory, since there are some misconceptions about it (exactly since some people interpret SOA = request / response). I may dedicate another blog to in-depth discussion about this two concepts. A side point - since this blog deals with "event processing", event processing is not implemented on top of EDA -- there are some cases in which event processing has "request-response" functions such as: getting events in PULL from the producer, which may be done periodically or on-demand, or event processing network that is implemented as part of transaction, and thus does not fulfill the loosely coupled principle of SOA. Thus "event processing" is not a pure EDA.... confused ?
more - later.

VLDB - and computer science 2.0

Hello from Vienna. Today the VLDB conference started with an interesting talk of Werner Vogels the CTO of Amazon, whose blog is entitled: AllThingsDistributed, and the framework they have built (and that other retailers use), he referred to Amazon as a technology company that happens to do retail. I think that there many touch points of event processing technology with the Amazon model, but did not find him to talk about it. I am Amazon customer for years, somewhere in the late nineties I remember ordering a bunch of books from Amazon, and not receiving them in the designated time, I have sent an Email to Amazon asking about it, the answer amazed me: we don't know what happened, we are sending the order again. A day later I received the original shipment, and sent another Email to Amazon - I got the original shipment, you may stop the substitute one, the answer I got was even more amazing: We cannot trace an order once it was issued, keep the books with our compliments". It seems that now they know how to track their order.

Other two keynote speakers have been Mike Stonebraker and Michael Brodie, two old-timers, who have been around for a while. Stonebraker gave some variation about his repeating message: "One size fits all: A concept whose time has come and gone" which talk about the elephants (Oracle, Microsoft, IBM) DBMS product as an obsolete concept, and shows that for various types of functionality (including "stream processing", of course), a specialized engine is better than a monolithic one, and in fact, the monolithic engines excel at nothing and should be eliminated. The idea that one size does not fit all is probably true, in databases (and also in event processing), one thing to note (and this follows also Mike's talk in EDAPS yesterday), he looks on everything in a single criterion -- speed (latency ?), I think that reality is a little bit more complex.

Mike Brodie started with a nice video with music that was getting louder showing facts about quantities -- size of various databases, internet webpages, use of search engines etc -- and trend (the time everything is duplicated is getting shorter and shorter), he also talked briefly about SOA, and about the need to take a new approach that is application-based, semantics-based, and create Computer Science 2.0 -- however I did not understand what new science is required, and in response to a question he answered --- I presented the problems, leaving the solutions to you. I am not sure that I have understood the problem (except for engineering issues), but let's wait to see if computer science 2.0 will arrive (I think that the term 2.0 is starting to be over-hyped, there were some attempts at SOA 2.0 as combination of SOA and EDA, but I am not sure it caught as a buzzword). Anyway -- whatever Computer Science 2.0 is -- event processing should be one of its fundementals. More later.

EDAPS-07 and event processing research community

Hello from Vienna again. Today the event processing meetings festival, that started in the EPTS meeting exactly a week ago, continued (and ended) in Vienna with the EDAPS workshop adjecent to the VLDB conference. The EDAPS workshop was chaired by Ling Liu and myself. Unlike the previous meetings, EDAPS is a scientific workshop, where the accepted papers were selected by a program committee. This has been the second time we are doing this workshop, and it was attened by around 20 people with interesting papers. One of the issues we have discussed in the closing session is the creation of a unified research conference, this year there have been three such conferences: DEBS 2007, DEPSA 2007 and EDAPS, besides that other conferences like RULE-ML 2007 has some track on "reaction rules", while database conferences have tracks on "streams". Indeed, event processing has many roots - verification/simulation, active databases, stream management, pub/sub, distributed computing, rules, programming languages, sensor networks and maybe I forgot something, but the challange is to try and devise a community of researchers whose primary discipline will be event processing. A first step is to try and devise one annual conference that will unify all forces. We have proposed the DEBS steering committee to open up and make DEBS such a conference, as the "flagship" of the event processing community, and decided in 2008 not to hold EDAPS instance, to give a chance to DEBS to build a strong conference. Alex Buchmann who will chair the program committee of DEBS 2008 in Rome will work to extend the program committee and we'll help him recruit industry/vendors participation. In my opinion, a research community associated with event processing is important for the existance of event processing as an area and discipline.

One last comments about EDAPS - we have invited Mike Stonebraker to be keynote speaker, Mike is certainly a great speaker, however, he has chosen to wear his vendor hat, and provided sales pitch, with some assertions and generalizations that I wonder if Mike Stonebraker the distinguished scientist would have accepted for publication... well. Tomorrow, the VLDB conference - more later.

Baggage handling -- how event processing can help people like me

Hello from Vienna, Austrtia. The baggage carousel was (almost) the first thing I have seen in Vienna airport, those who know me realize that this is one the places I most dislike, trying hard not to check luggage, which usually work (I am travelling with slight overweight on my carry-on luggage, but most airlines allow it), but I came across a strict (manual) agent in the Swiss ticket counter in Miami, and thus, had to deposit (in Hebrew there is a one letter difference between the word meaning "deposit" and the word meaning "abandon", so I always use the second word to describe hadning out luggage to an airline. I don't trust airlines to get my luggage in time - over the years, my luggage did not get on time three times, which may not be considered a lot, considered my travel quantity, but believe me, any such time is a big hussle. Moreover, I have read a statistics that 1.5% of the luggages don't get on time. Anyway, today there was an happy end -- after 10 minutes of wait I got my luggage and hurried out of there. Since this blog is about event processing and not about my personal eccentricities, I am thinking how event processing can help airlines to restore the confidence in the buggage handling systems and make neurotic passengers like me more relaxed -- well: it seems that all types of event processing can play here:

• Trace and track system with notification can be used to have the passenger ask questions (or get notifications) that notify that the luggage is on the right aircraft, and when standing near the carousel, provide an estimate when it is coming (with some RFID readers all over).


• BAM system that determines if something is going wrong --- the luggage did not arrive to some place, or arrived to the wrong place.


• Automatic decision system which re-routes the luggage, if the passenger was reassigned.


• Anything else ?

I will personally will be willing to pay for a service that notifies me the status of my checked luggage, espcially when standing near this carousale... this is not very difficult to construct...

Another small matter is the "ultra personalization", after arriving to Austria, not only people are talking to me in German, but also computerized system, I had to purchase Internet time in my hotel - T-Mobile has German only text, and after series of guesses, and some trial and error, I have succeeded to log it. This blogger system also talks German to me now -- in fact this is not personalization, this is location-based classification with wrong assumptions.... which brings to an interesting discussion about the term "context", which I view to be one of the major abstractions useful also in event processing -- more about it later.