Ph.D. - geht es zur Homepage der Informatik des Fachbereiches 3 ...

Chapter 7. openETCS Meta Model
far as possible. Furthermore, the meta model must be formal [78, Ch. 11]. Hence, the complete
concrete syntax and the static semantics must be completely defined. A formal representation
of the dynamic semantics can support this feature of the meta model.
This chapter starts with the selection of the used parts or rather the subset 3 of the ETCS SRS
for the case study because this must already be taken into account during the development of
the openETCS meta model. The concrete syntax [46, p. 70] of the meta model is explained by
the GOPPRR formalisms for sub-graphs, graph bindings, and type properties from Section 4.1,
which mainly corresponds to the concrete syntax used in MetaEdit+. Furthermore, the static
semantics [46, pp. 69-70] are defined by using the GOPPRR (C++) abstract syntax with OCL,
which is a set of constraints for any instance of the openETCS meta model. Afterwards, the
dynamic semantics [46, pp. 69-70], which means the behavioural interpretation of the meta
model, is discussed followed by a mathematical model for the dynamic semantics.
7.1. Selection of Specification Subset
Due to the complexity of the ETCS specification, even of the Subset-026 of the SRS, the
modelling of the complete SRS would no be realisable in the scope of this work. Therefore, a
certain and small enough subset of the SRS was selected for the case study:
• EVC implementation (mainly Subset-026)
– ETCS Application Levels: 0, 1
– ETCS Modes:
∗ No Power (NP)
∗ Stand By (SB)
∗ System Failure (SF)
∗ Isolation (IS)
∗ Trip (TR)
∗ Post Trip (PT)
∗ Unfitted (UN)
∗ Staff Responsible (SR)
∗ Full Supervision (FS)
This reduced subset of the SRS should directly influence the complexity of the later introduced
model instance. On the other hand, the limitation to the Application Levels 0 and 1 means
that only Eurobalises are used for track-to-train communication. As device types are also
included in the meta model, which is explained in the following section, this already reduces
the complexity for the meta modelling process.
The aim of this specification subset and the corresponding DSM instances is to provide
a minimal executable case study for the EVC that proves the feasibility of the open model
concept. Necessary extensions to all DSM instances needed for covering all SRS parts should
not be a reduction of this prove. Hence, those extensions were also taken into account during
the DSL development but are not (yet) implemented.
3 Subset does not refer here to the term used in the ETCS SRS for combining several chapters, for example,
Subset-026.
80