Butler, Michael

Snook, Colin

English

Southampton (e-Prints Soton)

UML-B: A plug-in for the Event-B tool set1 Colin Snook and Michael Butler University of Southampton, United Kingdom {cfs,mjb}@ecs.soton.ac.uk  UML-B  is  a  graphical  formal  modelling  notation  that  relies  on  Event-B  for  its underlying semantics and is closely integrated with the ‘Rodin’, Event-B verification tools. UML-B is similar to UML but has its own meta-model. UML-B provides tool support, including drawing tools and a translator to generate Event-B models. When a UML-B drawing is saved the translator automatically  generates the corresponding Event-B model. The Event-B verification tools (syntax checker and prover) then run automatically providing an immediate display of problems which are indicated on the relevant UML-B diagram. The UML-B modelling environment consists of a UML-B project containing a UML-B model. Four interlinked diagram types (package, context, class  and  statemachine)  are available.  Package  Diagrams  are  used  to describe  the ‘refines’  and  ‘sees’  relationships  between  top  level  components  (machines  and contexts) of a UML-B project. UML-B mirrors the Event-B approach where static data (sets and constants) are modelled in a separate package called a ‘context’. The context diagram is similar to a class diagram but has only constant data represented by  ClassTypes,  Attributes  and  Associations.  ClassTypes  define  ‘carrier’  sets  or constant subsets of other ClassTypes. ClassTypes may own immutable attributes and associations which represent constant functions. The behavioural parts (variables and events) are modelled in a Class diagram which is used to describe the ‘machine’. Classes represent subsets of the ClassTypes that were introduced in the context. The class’  associations  and  attributes  are  similar  to  those  in  the  context  but  represent variables instead of constants. Classes  may own events that  modify the  variables. Event parameters can be added to an event, providing local variables to be used in the transition’s  guards  and  actions.  Class  events  utilise  a  parameter,  self,  to  non-deterministically select the affected instance of the class. State machines may be used to model behaviour. Transitions represent events with implicit behaviour associated with  the  change  of  state.  Additional  guards  and  actions  can  be  attached  to  the transition. UML-B retains sufficient commonality with UML for the main goals of approachability  to  be  attained  by  industrial  users.  Since  UML-B  automates  the production  of  many  lines  of  textual  B,  models  are  quicker  to  produce  and  hence exploration of a problem domain is more attractive. This assists novices in finding useful abstractions for their models. We have found that the efficiency of UML-B and its ability to divide and contextualise mathematical expressions assists novices who would otherwise be deterred from writing formal specifications. UML-B is also a useful visual aid for more experienced formal methods users.                                                             1  This  work  was  carried  out  under  the  EU  projects,  Rodin  [IST-511599]  and  ICT  project Deploy [IP-214158]. 

UML-B: A plug-in for the Event-B tool set

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Southampton (e-Prints Soton)