In a previous blog post, a playful concrete example was given to show off PSL's newly added support for IEEE 754 floating point calculations. We have tested the performance in real world industrial examples and in this blog post we will take a look at the floating point performance of PSL on a real world [...]
Hopefully you have read part 1 on this blog, where I tried to convince you that traditional methods will not get you very far when verifying safety requirements for railway interlockings. This time my task is to convince you that formal verification will get you far. In fact, all the way. So what is formal [...]
The subject I am going to write about this time is not an easy one. I will try to explain why formal verification is good. In particular, why it is a good practice to use formal verification when verifying safety requirements on railway systems. The Verification Problem In order to make a convincing argument, I [...]
In a recent post we celebrated the 10th anniversary of the declarative, formal language HLL. The language is used extensively in the railway signaling domain for the formal verification of interlocking logic and CBTC subsystems (such as zone controllers). In this more technical post we will familiarize the reader further with HLL, by formalizing the famous [...]
The formal language HLL (High Level Language) has emerged in recent years as a quite popular language for formal verification of safety-critical systems, especially in the railway signaling domain. This year marks the 10th anniversary of its conception. The history of HLL The language has its roots in the proof engine technologies developed by Prover in the 1980s (Stålmarck's [...]
We've all been there, waiting for the theorem prover to answer. Getting up for a cup of coffee, bugging a colleague... still no answer. This can be standard behaviour when doing formal verification. The requirements are difficult to prove, the system manages to escape into some dark corner not easily approached by the theorem prover. [...]
Back in March this year I wrote about a work package on formal methods and standard interfaces, led by the Swedish Transport Administration (Trafikverket, and part of the European Shift2Rail (S2R) Joint Undertaking. Since that time, the proposal for the overall project that includes this work package has been submitted and become approved, and the project started [...]
In the early days of railway history there were no interlocking systems. It was considered enough to have personnel at the train stations manually observing trains and operating signals. The need for automatic signalling eventually became evident: human beings tend to make mistakes, which can lead to serious accidents, and the capacity of railroads was [...]
The digitalized railway signaling systems of today are becoming increasingly complex with more and more functionality added to make better use of the existing infrastructure, while maintaining the highest level of safety. This also means that the task of assessing the safety and function of these system becomes more and more complex and often constitutes [...]
Railway signaling systems are surprisingly expensive to produce. Why did this happen? In the early days of railway history there were no interlocking systems. It was considered enough to have personnel at the train stations manually observing trains and operating signals. The need for automatic signalling eventually became evident: human beings tend to make mistakes, [...]
