Frank's Blog

Welcome to the Exhibition 

I know quite some people that are a bit unsure about the things we do all day long. Instead of talking about something they don't understand (it can be found here), actually, our institute has something new to offer: An exhibition of modern art. Take a look at these pictures and objects that have been placed at nearly every possible place. And yes, these pictures/objects are all original ones...










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Me with a Hat 

Yesterday I defended my doctoral thesis and finally got one of those funny hats. While my thesis will appear later this month on this website, you can already find the slides here (in German).


The reviewers of my thesis (from left to right): Prof. Weske (HPI), Prof. van der Aalst (TU Eindhoven), Prof. Nestmann (TU Berlin).


The buffet.


And finally, me with a hat (in the background is Prof. Naumann, the chairman of my defense).
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PowerBook survived Surgery OR Always make a Backup 

Yesterday, my good old PowerBook 12" (yes, the lightest Apple notebook ever produced until now), unexpectedly died right in front of a class. I was giving a lecture on the pi-calculus and BPM (what else?), as Keynote did not started the presentation right away. Instead, the Keynote dock symbol bounced up and down and the beachball occured. The only things I was able to do was move the mouse. After investigating the issue, I found out that the harddrive made a metallic click noise. This came a bit unexpected, since the day before yesterday I thought about updating my backup...

Nevertheless, I went to K&M and picked up a nice 160GB Samsung harddrive. This morning, I prepared everything according to http://www.ifixit.com/, removed about 35 screws, placed the new hdd into place, assembled 35 screws---and---finally got a working PowerBook with an even faster harddisk. This is how the book looked before the old drive had been removed:



What do we learn thereof? Always make a backup!
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Compatibility and Conformance 

Welcome back to the research session. This time I've been explaining the difference between compatibility and conformance and raise the issues that need urgent research. Both terms are related to the area of service-oriented architectures:

Compatibility is the property of two or more services working seamlessly together. Usually, one service is treated as the requester, meaning it is the starting point for investigation. Seamlessly means without any deadlocks. Hence, compatibility extends traditional investigations of soundness for process-internal structures to a set of services. I always rely on interaction soundness, since it's a simple - but yet powerful - kind of compatibility notion. In a sentence, interaction soundness proves a business process to be compatible with a set of predefined services that can be dynamically bound to the requesting process.

Conformance is the property of a service implementation to share certain invariants with its specification. As can already be concluded, a useful definition of conformance is quite complicated. Traditionally, we can argue that a service implementation and specification are conform if both have the same observable behavior, i.e. they are bisimulation equivalent. While bisimulation equivalence is a valid property, it is too strong regarding practical application. Consider for instance:



where an explicit choice has already been made at design-time. While this might be a wanted refinement, specification and implementation are not conformant regarding bisimulation equivalence (Since the implementation cannot receive an expertise).

Another common conformance notion is simulation. If the specification can simulate anything the implementation can do, both should be conformant. In fact, this solves the problem illustrated with bisimulation. It raises, however, compatibility issues. Consider for instance the following figure



where two specification are compatible (i.e. they always interact deadlock free) but both implementations (that conform to the specifications according to simulation) are not compatible anymore! Indeed, it would be enaugh for both specification to only have their first activity and still be similar to their specifications!

The examples illustrated some of the problems that occur using bisimulation and simulation as conformance notions. We're currently working hard to find a suitable solution.
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Chicago Pics 

Just as the temperature (and humidity) is melting us, here are some pictures from my Chicago trip.This has already taken place in December, with temperatures as low as -20C:


My hotel.


The local Apple store.


The Chicago river at night.


The public transportation above the streets.


Starbucks in the old part of the town.


The Chicago river once more.


The Chicago board of trade.


Skyline view from the Sears tower.
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