Lecture Notes in Computer Science 3472

18 Run-Time Verification 551
gather data from online services. Then, they compute invariants over multiple
numeric fields by Daikon and compute invariants over single numeric fields by
statistic estimations [RKS02]. Invariants can be used to monitor the evolution of
data feed systems with respect to both updates to implemented functionalities
and sensible modifications on data sources. Verification is performed at the clientside
and can be used to check multiple data feed systems providing similar
services.
The Behavior Capture and Test (BCT) [MP05] technique verifies at run-time
learned invariants in the case of component-based and object-oriented software
even without requiring source code. BCT uses the Object Flattening technique
to automatically extract state data from objects. Object Flattening recognizes
non-intrusive methods, named inspectors, of a given object by a heuristic. Selected
inspectors are then invoked to get the internal state of the object. In
case the internal state is an object, the approach is recursively applied until a
given depth or until a primitive data type is obtained. Heuristical selection of
inspectors is based on both language introspection, to automatically gather the
signature of the methods, and conventions on writing code, to select inspectors
by syntactic information. The behavior of the Object Flattening technique is
highly configurable and can be adapted to arbitrary enterprise notations. Once
state data has been extracted, BCT uses the invariant inference engine implemented
in Daikon to derive invariants.
BCT infers also interaction invariants representing the interaction protocol
used by components to interact. This protocol is synthesized in a regular expression
summarizing all observed behaviors. Letters of the alphabet used to
define regular expressions correspond to methods implemented by components
of the system, and the language generated by a given regular expression of a
component C corresponds to all acceptable behaviors that the component C can
perform. In particular, the regular expression is derived by merging the observed
interaction patterns and by generating new behaviors as natural generalization
of the observed one [MP05].
BCT checks at run-time both interaction and object-oriented invariants by
automatically generated monitors which capture both requests and results of
performed computations.
Debugging by Invariants The DIDUCE tool [HL02a] instruments the source
code to derive invariants that are continuously verified and updated at runtime.
The technique seriously takes into consideration the amount of consumed
resources, thus lightweight computations of invariants is obtained at the cost of
limited expressiveness power of the inferred invariants. In fact, the instrumentation
consists of checking equality of object references, static variables, input
parameters and return values, with respect to a fixed value. Invariants are relaxed
upon violation, in particular a mask defines the bits that must be checked
for equality. Each time the equality between the expected value and the observed
value is falsified for a bit, the mask is modified and the corresponding bit is not
checked anymore. The inference technique consumes little time and memory, but