This paper introduces different views for understanding problems and faults
with the goal of defining a method for the formal specification of systems. The
idea of Layered Fault Tolerant Specification (LFTS) is proposed to make the
method extensible to fault tolerant systems. The principle is layering the
specification in different levels, the first one for the normal behavior and
the others for the abnormal. The abnormal behavior is described in terms of an
Error Injector (EI), which represents a model of the erroneous interference
coming from the environment. This structure has been inspired by the notion of
idealized fault tolerant component but the combination of LFTS and EI using
Rely/Guarantee reasoning to describe their interaction can be considered as a
novel contribution. The progress toward this method and this way to organize
fault tolerant specifications has been made experimenting on case studies and
an example is presented.Comment: Presented and published at DEPEND 201