'Leveled' Conformance Tests - A Must for Interoperability

Modular design and networked solutions are the basic answers to master complexity of today’s and future systems. Complexity will even grow dramatically as the desired functionality by the end user is increasing drastically. A basically efficient approach to achieve proper interoperability in distributed systems is to apply standard 'layers' onto which the application itself is built, to specify standard layers as high as possible while minimizing the individual application parts and to check the functionality of these layers by sufficiently efficient conformance tests. In automotive and other applications these 'standard' layers comprise – from the lowest to the highest level – the 'transceiver' layer, the 'network' layer, a 'device driver interface' layer and the 'operating system' layer, which currently is the final interface to the application. In automotive applications the communication layers mostly are based on CAN protocol complemented by CAN software drivers interfacing the operating system OSEK/VDX.This stack of 'standard' levels provides a powerful and neutral interface to the application. But experience over the last years has shown that the implementations of the individual levels differ in their behavior. This is due to several reasons such as the specifications of the individual levels are not precise enough, they are ambiguous, they difficult to implement because of their complexity. Even if there formal and executable specifications for instance based on state machine languages, implementations show defects because the implementers try to optimize and thus they violate unknowingly for instance the constraints related to local variables.