Information Technology Reference
In-Depth Information
Fig. 3. Divergent interpretation of a common public domain ETCS System Re-
quirement Specification (SRS) document, due to the “human factor” by all par-
ties involved, causing different software solutions with deviant behavior of products
from different manufacturers, which result in interoperability deficiencies and costly
subsequent improvement activities.
2.4
Life Cycle of Complex Software
While on the one hand, electronic components are becoming increasingly
powerful, yet lower in cost, on the other hand, cost levels of complex software
products are increasingly rising not only because the amount of code lines
need tremendous men power, but for those lines of code a poof of correctness,
or also called “safety case”, has to be delivered in order to reach approval
for operation in revenue service. Some manufacturers have already reported
software volumes of over 250 TLOC for the ETCS core functionality defined
by ETCS SRS subset 026 [1].
It is very dicult to receive reliable statistics about errors on safety re-
lated soft-ware products, because almost all software manufacturers hide their
source code using proprietary license agreements. However we can assume
that software in other mission critical systems, like communication servers,
may have the same characteristics with respect to “bug counts”. One of those
rare examples published, was taken from an AT&T communication software
project, which from its size is in the same order of magnitude as today's
ETCS onboard software packages (figure 4) [9],[13].
One particular characteristic in figure 4 is quite obvious: The size of the
software is continuously growing from version to version, despite the fact
