2 Why We Need Model-Based Testing

276 Further Reading
An approach of using scenario style modeling with model programs written in
AsmL (see, e.g., Gurevich et al., 2005) was elaborated in Grieskamp et al. (2004).
In order to address a practical demand of Spec Explorer (SpecExplorer, 2006) users,
a limited support for scenario-oriented modeling was added to the Spec Explorer
tool through scenario actions. In Spec Explorer, the user can write models either
in AsmL (Gurevich et al., 2005) or in Spec# (Barnett et al., 2005). The need for a
general notion of composition, in order to handle other forms of scenario control and
parameter generation, has been discussed in several sources (Campbell et al., 2005a;
Veanes et al., 2005, 2007a). In this context, action machines have been proposed to
compose partial behavioral descriptions as a variation of symbolic-labeled transition
systems (Grieskamp et al., 2006).
The use of scenarios in the form of live sequence charts is discussed as a way
both to model and to program reactive systems with the Play-Engine (Harel and
Marelly, 2003).
The idea of property checking using model program composition (see Section
14.4.4) is related to the automata theoretic approach to model checking where an
automaton corresponding to the negation of the property to be checked is composed
with the model (Clarke et al., 1999; Holzmann, 2004).
Modeling objects. The formal treatment of objects is based on the notion of reserve
elements from the ASM theory (Gurevich, 1995). In particular, creation of a new
object corresponds to importing of a reserve element. The support for modeling with
objects was already supported in the AsmL-T tool (Barnett et al., 2003) that is the
predecessor of Spec Explorer. Support for dynamic object graphs was also present
in the Agedis tools (Hartman and Nagin, 2004).
The state isomorphism problem discussed in Section 15.5 arises when unordered
data structures and objects are combined and is as hard as graph isomorphism
(Ullmann, 1976; McKay, 1981). The problem occurs very frequently. Already the
standard Spec Explorer example known as the chat system uses objects as well as
sets and maps; see Utting and Legeard (2006, Section 6.5) for a detailed exposition
of this example. The state isomorphism problem was not solved in Spec Explorer.
If objects are not used, then state isomorphism reduces to state equality that can
be checked in linear time. This is possible because the internal representation of
all data structures can then be canonicalized. The same argument is true if objects
are used but all data structures are ordered. Then state isomorphism reduces to
heap canonicalization in the context of model checking and can be implemented in
linear time (Iosif, 2004; Musuvathi and Dill, 2005). Bogor (Robby et al., 2006)isa
customizable software model checking engine that uses the method of Iosif (2004)
to perform heap canonicalization based on an ordering of object ids. Korat (Boyapati
et al., 2002) is a tool for automated test generation based on Java specifications. It also
uses the concept of heap isomorphism. Symstra (Xie et al., 2005) uses a technique
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