Current Limitations

Revision as of 09:18, 31 August 2015 by Michael Leuschel (talk | contribs)

ProB in general requires all deferred sets to be given a finite cardinality. If no cardinality is specified, a default size will be used. Also, unless finite bounds can be inferred by the ProB constraint solver, mathematical integers will only be enumerated within MININT to MAXINT (there is now some support for checking whether such an enumeration did occur, in particular when using the commands in the "Analyse Predicate" sub-menu).

Other general limitations are:

  • closure. The transitive and reflexive closure operator of classical B, named closure, does not follow exactly the definition from the B-Book by Abrial. AtelierB also does not support the operator as defined in the B-Book (as this version cannot be applied in practice). For the reflexive component of closure, ProB will compute the elements in the domain and range of the relation (i.e., for ProB we have closure(r) = closure1(r) \/ id(dom(r) \/ ran(r))). As an example, closure({1|->2}) equals {1|->1,2|->2,1|->2} in ProB, but is infinite according to the B-Book : {1|->2, 0|->0, 1|->1, -1|->-1, 2|->2,...}.

Note however, that the transitive closure operator closure1 is fully supported, and hence one can translate an expression closure(e), where e is a binary relation over some domain d, into the expression closure1(e) \/ id(d).

  • Trees and binary trees. These constructs are specific to the AtelierB tool and are not supported (the STRING type is now supported);
  • Definitions. Definitions (from the DEFINITIONS clause) with arguments are supported, but in contrast to AtelierB they are parsed independently and have to be either an expression, a predicate, or a substitution; definitions which are predicates or substitutions must be declared before first use. Also: the arguments of DEFINITIONS have to be expressions. Finally, when replacing DEFINITIONS the associativity is not changed. E.g., with PLUS(x,y) == x+y, the expression PLUS(2,3)*10 will evaluate to 50 (and not to 32 as with Atelier-B).

  • There are also limitations with refinements. See below;
  • VALUES This clause of IMPLEMENTATION machines is not yet supported;
  • Parsing: ProB will require parentheses around the comma, the relational composition, and parallel product operators. For example, you cannot write r2=rel;rel. You need to write r2=(rel;rel). This allows ProB to distinguish the relational composition from the sequential composition (or other uses of the semicolon).

See the page Using ProB with Atelier B for more details.

Multiple Machines and Refinements

It is possible to use multiple B machines with ProB. However, ProB may not enforce all of the classical B visibility rules (although we try to). As far as the visibility rules are concerned, it is thus a good idea to check the machines in another B tool, such as Atelier B or the B-Toolkit.

While refinements are supported, the preconditions of operations are not propagated down to refinement machines. This means that you should rewrite the preconditions of operations (and, if necessary, reformulate them in terms of the variables of the refinement machine). Also, the refinement checker does yet check the gluing invariant.

Note however, that for Rodin Event-B models we now support multi-level animation and validation.