Practicas y usos de equipos e instrumentos de laboratorio

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J. Software Engineering & Applications, 2010, 3: 303-311
doi:10.4236/jsea.2010.34036 Published Online April 2010 (http://www.SciRP.org/journal/jsea)

Separation of Fault Tolerance and Non-Functional
Concerns: Aspect Oriented Patterns and
Evaluation
Kashif Hameed, Rob Williams, Jim Smith
University of the West of England, Bristol Institute of Technology, Bristol, UK.
Email:{Kashif3.Hameed, Rob.Williams, James.Smith}@uwe.ac.uk
Received January 1st, 2010; revised January 30th, 2010; accepted February 1st, 2010.

ABSTRACT
Dependable computer based systems employing fault tolerance and robust software development techniques demand
additional error detection and recovery related tasks. This results in tangling of core functionality with these cross cutting non-functionalconcerns. In this regard current work identifies these dependability related non-functional and
cross-cutting concerns and proposes design and implementation solutions in an aspect oriented framework that modularizes and separates them from core functionality. The degree of separation has been quantified using software metrics.
A Lego NXT Robot based case study has been completed to evaluate theproposed design framework.
Keywords: Aspect Oriented Design and Programming, Separation of Concerns, Executable Assertions, Exception
Handling, Fault Tolerance, Software Metrics

1. Introduction
Adding fault tolerance (FT) measures and other nonfunctional requirements to safety critical and mission
critical applications introduces additional complexity to
the core application. Byincorporating handler code, for
error detection, checkpointing, exception handling, and
redundancy/diversity management, the additional complexity may adversely affect the dependability of a safety
critical or mission critical system.
One of the solutions to reduce this complexity is to
separate and modularize the extra, cross-cutting concerns
from the true functionality.
Although Rate of Change (ROC)based plausibility
checks for error detection and recovery have been addressed by [1,2], unfortunately none of the previous studies propose the separation of these error handling concerns from true functionality to avoid complexity.
At the level of design and programming, several approaches have been utilized that aim at separating functional and non-functional aspects. Component level approachlike IFTC [3], computational reflection and meta-object protocol based MOP [4] have shown that dependability issues can be implemented independently of
functional requirements.
The evolving area of Aspect-Oriented Programming &
Design (AOP&D) presents the same level of independCopyright © 2010 SciRes

ence by supporting the modularized implementation of
crosscutting concerns.Aspect-oriented language extensions, like AspectJ [5]
and AspectC++ [6] provide mechanisms like Advice (behavioural and structural changes) that may be applied by
a pre-processor at specific locations in the program
called join point. These are designated by pointcut expressions. In addition to that, static and dynamic modifications to a program are incorporated by slices which can
affect the staticstructure of classes and functions.
The current work thus proposes some generalized aspect oriented design patterns representing fault tolerance
error detection and recovery mechanisms like ROC plausibility checks, exception handling, checkpointing and
watchdog. Moreover some additional design patterns for
developing robust mission/safety critical software are also
presented. Software metrics likecoupling, cohesion and
size have been applied quite successfully to access and
evaluate the quality attributes of OO software systems [7,
8]. However separation of concerns (SOC) especially
cross cutting ones in the light of new abstraction addressed by AO software development demands some additional metrics. The current work reviews these additional metrics like concern diffusion over the...