Page 105 - 360.revista de Alta Velocidad - Nº 5

Test and Certification of Railway automation and digitalization approaches (Rail 4.0)

The second way formal methods enter the testing process is in the automation of test construction.
The elaborations in the preceding sections illustrate the highly nontrivial task of constructing a
test set. In arranging test cases for the ETCS OBU, the Chinese postman algorithm has been used
to find a first solution, which led to a stable test suite only after extensive work on parameter
instantiation and calibration. Getting the timing, position and velocity parameters right proved
to be rather difficult.
The construction of test sequences for track-side equipment is less difficult with respect to
real-valued parameters, but on the other hand has to solve issues with testing generic systems
which are to be instantiated to control a particular local arrangement of track elements. Testing
is done on one or few sample layouts. To allow a flexible arrangement in test sequences, test
cases should be formulated in a parametric style, permitting their instantiation depending on
the needs of other test cases.
In both cases, formal languages for parametric test case specification are used, and algorithms
for optimizing the arrangement into sequences are applied. These formal based solutions are
still to be improved upon, as the currently available techniques have a limited scope and
achieve non-optimal results.

7. Conclusion

The approach used for the conformity tests and operational tests for ETCS is proven in use
and can therefore be extended for testing ATO functionalities and interfaces, too. As long as
the interfaces are functional and digital the methodology can be reused easily. It may, like for
interface conformity, even applied to partial standardisations. The principle method of the
generation of the test sequences can be used for the different types of tests. The optimization
criteria as well as the rules for the parameterization differ for the different kinds of tests. If
the same approach for the formalisation and parameterization is used, the lab environment can
be used for any type of test, with, however, some adaptations to be made to achieve sufficient
flexibility.

Test case generation as well as test sequence construction profit substantially from the
application of formal approaches. This field features a variety of languages, methods and
tools. Present-day solutions cover only part of the needs of practice, but show potential to be
much more useful if embedded applied in a carefully designed process employing adequate
formalisations.
Future approaches for digitalisation of rail traffic management systems, train control systems
or interlocking focus on a stronger modularisation and standardisation. Therefor the same
approach should be applied to ensure conformity and interoperability of the modules of such
digitalized components. By applying this proven-in-use approach the cost and time required for
the tests can be reduced up to the final goal of zero field test .

8. References

• [1] ERTMS -- Test Sequences, SUBSET-076-6-3, Version: 3.0.0, 1/06/2016
• [2] ERTMS -- System Requirements Specification. SUBSET-026, Version 3.4.0, 15/06/2016

• [3] ERTMS -- Test Sequence Generation: Methodology and Rules. SUBSET-076-4-1, Version
1.0.2, 1/07/2016

• [4] ERTMS -- Methodology of testing. SUBSET-076-3, Version 2.3.1, 1/07/2016
• [5] ERTMS -- Functional requirements for an on-board reference test facility, Version:3.0.0,
15/06/2016

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