4 research outputs found
An algorithm for dynamic reconfiguration of mobile agents
In this paper we show an algorithm for dynamic reconfiguration of distributed applications based on the mobile agent model. We also show that the proposed algorithm can be easily implemented in the IPL language, a language with several abstractions for the construction of mobile applications in the Internet.Facultad de Informátic
Structuring fault-tolerant object-oriented systems using inheritance and delegation
PhD ThesisMany entities in the real world that a software system has to interact with, e.g.,
for controlling or monitoring purposes, exhibit different behaviour phases in their
lifetime, in particular depending on whether or not they are functioning correctly.
That is, these entities exhibit not only a normal behaviour phase but also one or
more abnormal behaviour phases associated with the various faults which occur
in the environment. These faults are referred to as environmental faults. In the
object-oriented software, real-world entities are modeled as objects. In a classbased
object-oriented language, such as C++, all objects of a given class must
follow the same external behaviour, i.e., they have the same interface and associated
implementation. However this requires that each object permanently belong
to a particular class, imposing constraints on the mutability of the behaviour for
an individual object. This thesis proposes solutions to the problem of finding
means whereby objects representing real-world entities which exhibit various behaviour
phases can make corresponding changes in their own behaviour in a clear
and explicit way, rather than through status-checking code which is normally
embedded in the implementation of various methods.
Our proposed solution is (i) to define a hierarchy of different subclasses related to
an object which corresponds to an external entity, each subclass implementing a
different behaviour phase that the external entity can exhibit, and (ii) to arrange
that each object forward the execution of its operations to the currently appropriate
instance of this hierarchy of subclasses. We thus propose an object-oriented
approach for the provision of environmental fault tolerance, which encapsulates
the abnormal behaviour of "faulty" entities as objects (instances of the above
mentioned subclasses). These abnormal behaviour variants are defined statically,
and runtime access to them is implemented through a delegation mechanism which
depends on the current phase of behaviour. Thus specific reconfiguration changes
at the level of objects can be easily incorporated to a software system for tolerating
environmental faults
A testbed for embedded systems
Testing and Debugging are often the most difficult phase of software development. This is especially true of embedded systems which are usually concurrent, have real-time performance and correctness constraints and which execute in the field in an environment which may not permit internal scrutiny of the software behaviour. Although good software engineering practices help, they will never eliminate the need for testing and debugging. This is because failings in the specification and design are often only discovered through testing and understanding these failings and how to correct them comes from debugging. These observations suggest that embedded software should be designed in a way which makes testing and debugging easier and that tools which support these activities are required. Due to the often hostile environment in which the finished embedded system will function, it is necessary to have a platform which allows the software to be developed and tested "in vitro". The Testbed system achieves these goals by providing dynamic modification and process migration facilities for use during development as well as powerful monitoring and background debugging support. These facilities are built on a basic run-time harness supporting an event-driven programming model with a global communication mechanism. This programming model is well suited to the reactive nature of embedded systems. The main research contributions of this work are in the areas of finding deadlock-free, path-optimal routings for networks and of dynamic modification with automated conversion of data which may include pointers