@techreport{TR-IC-12-18,
   number = {IC-12-18},
   author  =  {Amanda  S.  Nascimento and Fernado Castor and Cec\'ilia
                   M.F. Rubira and Rachel Burrows},
   title  =  {{An  Empirical Study on Design Diversity of Functionally
                   Equivalent Web Services}},
   month = {June},
   year = {2012},
   institution = {Institute of Computing, University of Campinas},
   note = {In English, 24 pages.
    \par\selectlanguage{english}\textbf{Abstract}
       A  number  of  approaches  leverage  software  fault  tolerance 
       techniques  based  on  design  diversity  to  tolerate software
       faults   in   service-oriented  applications.  These  solutions 
       moderate  the  communication  between  clients and functionally
       equivalent  services, i.e., variant services. The use of design
       diversity  depends  on the assumption that variants rarely fail
       on  the  same  input  case. Nevertheless, it is unclear whether
       variant  services  are  actually  diverse  and fail on disjoint
       subsets  of the input space. In a previous work, we proposed an
       experimental  setup  to  assess  design  diversity  of  variant 
       services  that  realize  a  requirements specification. In this
       work,  we utilize the proposed experimental setup to assess the
       design  diversity  of  a  number  of  third-party  Web services
       adhering  to  seven  different  requirements specifications. In
       this paper, we describe in detail the main findings and lessons
       learned  from  this  empirical  study.  Firstly, we investigate
       whether  variant  services  present difference in their outputs
       and  failure  behaviours to look for evidence that variants are
       provided  by different design and implementations. Secondly, we
       investigate   the   effectiveness   of  service  diversity  for 
       tolerating  faults. The results suggest that there is diversity
       in  the  implementation  of  variant services. However, in some
       cases, this diversity might not be sufficient to improve system
       reliability.  Our findings provide an important knowledge basis
       for engineering effective fault-tolerant ser vice applications.
  }
}