Specification of Reactive Hardware/Software Systems - Electronic ...

20 On Specification of Reactive Hardware/Software Systems
Other views are, as far as we have been able to check, not equipped with formal semantics.
If a method does support a unified model (which has our preference), this should
be expressed in a formal (executable) language. Separate views can then be expressed
informally, though accompanying formal descriptions are in this case welcome too. An
example of a method that starts with informal views and ends up with a formal unified
model is ROOA [Mor94].
The separate system views may be expressed in informal languages.
The unified system model must be expressed in a formal
language.
Software Tools
A major advantage of formal languages is that they have precisely defined syntax and
semantics. This ensures that formal models are consistent, precise and unambiguous.
Another major advantage of formal languages is that they allow the development of
advanced and indispensable software tools that support the specification process. Important
tools are
(a) Model editors, syntactic analysers, semantic analysers and documentation generators.
(b) Verification tools and dynamic analysers. For instance, equivalence checking or preorder
checking can be applied to verify whether the system model exhibits the same
observable behaviour as another system model (expressed in the same language)
derived in a previous design phase. Model checking can be used to verify whether
the system model satisfies behavioural properties expressed in a behavioural view
or timing properties expressed in a timing view. In this case, the views must be
expressed in a formal language too (for example in a temporal logic). Using a
dynamic analyser certain predefined dynamic properties can be checked.
(c) Simulation tools. These tools are used for verification and validation purposes, i.e.
for the checking whether the system models satisfies the informal requirements.
Simulation techniques can greatly increase the designer confidence in specifications
[Fuc92].
(d) Code generator tools. These tools automatically compile models into a target language
(such as C or VHDL).
(e) Transformation tools. These support the automatic transformation of models while
keeping certain properties invariant. For instance, behaviour-preserving transformations
change the structure of models, without modifying their observable
behaviour. They are used to keep behaviour views and architectural views consistent
or to integrate these views consistently into a formal unified model.
All of these tools are more or less implemented in the LotoSphere integrated tool environment
Lite [CS92]. In particular Lite supports equivalence checking and model
checking, compilation into the programming language C, and behaviour-preserving
transformations. SDL supports (a),(c) and (d) [Tur93]. SDL can be compiled to C, Pascal