# An Efficient Library for Reliability Block Diagram Evaluation
## 6 Conclusions and Future Work  
In this paper, we presented librbd, an open source optimized library for reliability evaluation using the RBD formalism. After the mathematical background description, we illustrated the library design and characteristics. Then, we showed its execution times on different platforms and performed a comparison with the most similar tool identified at the state-of-the-art. The good results achieved enable the usage of librbd in hierarchical approaches for reliability evaluation exploiting strengths of both combinatorial and state-space based models. In particular, the comparison experiments show that the execution time of librbd is, in general, almost 9 times faster than the one obtained using SHARPE. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**RBD Block**} & \multirow{2}{*}{**Topology**} & \multicolumn{2}{c}{**Execution Time (s)**} & \multirow{2}{*}{**Gain (\%)**} \\  & & librbd & SHARPE & \\ \hline \multirow{4}{*}{Series generic} & 2 & 0.10 & 0.98 & 89.95 \\  & 3 & 0.10 & 1.12 & 91.04 \\  & 5 & 0.11 & 0.98 & 88.97 \\  & 10 & 0.10 & 1.94 & 94.60 \\  & 15 & 0.10 & 2.59 & 96.19 \\ \hline \multirow{4}{*}{Series identical} & 2 & 0.10 & 0.90 & 89.24 \\  & 3 & 0.11 & 0.96 & 88.32 \\  & 5 & 0.11 & 0.90 & 87.72 \\  & 10 & 0.12 & 1.23 & 90.40 \\  & 15 & 0.10 & 1.45 & 93.31 \\ \hline \multirow{4}{*}{Parallel generic} & 2 & 0.11 & 0.98 & 89.08 \\  & 3 & 0.10 & 1.12 & 91.20 \\  & 5 & 0.11 & 0.98 & 89.22 \\  & 10 & 0.10 & 2.03 & 94.95 \\  & 15 & 0.10 & 2.78 & 96.36 \\ \hline \multirow{4}{*}{Parallel identical} & 2 & 0.10 & 0.92 & 89.19 \\  & 3 & 0.11 & 0.95 & 88.74 \\  & 5 & 0.11 & 0.92 & 88.51 \\  & 10 & 0.12 & 1.31 & 91.16 \\  & 15 & 0.10 & 1.59 & 93.85 \\ \hline \multirow{4}{*}{KooN generic} & 1 oo2 & 0.11 & 1.01 & 89.37 \\  & 2 oo3 & 0.12 & 1.15 & 89.95 \\ \cline{1-1}  & 3 oo5 & 0.11 & 1.01 & 89.44 \\ \cline{1-1}  & 5 oo10 & 0.15 & 2.28 & 93.21 \\ \cline{1-1}  & 8 oo15 & 2.35 & 3.36 & 29.96 \\ \hline \multirow{4}{*}{KooN identical} & 1 oo2 & 0.11 & 0.88 & 87.80 \\ \cline{1-1}  & 2 oo3 & 0.11 & 0.89 & 88.13 \\ \cline{1-1}  & 3 oo5 & 0.11 & 0.88 & 87.71 \\ \cline{1-1}  & 5 oo10 & 0.08 & 1.31 & 94.20 \\ \cline{1-1}  & 8 oo15 & 0.08 & 1.81 & 95.71 \\ \hline Bridge generic & 5 & 0.10 & 1.64 & 94.16 \\ \hline Bridge identical & 5 & 0.09 & 1.66 & 94.35 \\ \hline \hline \end{tabular}
\end{table} 
Table 15: Execution time comparison. These good results encourage the usage of librbd to implement a prognostics application that leverages a frequent computation of the tuned reliability curve. Future research and advancements of librbd include the following:  
* Development of a tool that allows the graphical definition of RBDs and their analysis through the usage of librbd. * Development of a tool that allows the graphical definition of hierarchical models (RBDs and STPNs/GSPNs) and that integrates librbd and SIRIO library for their quantitative evaluation. * Usage of native Windows APIs for SMP to decrease the execution time on this OS. * Investigation on the performance loss experienced for KooN block with generic components. This performance loss is visible with \(N=15\) and it is probably due to a nonoptimized usage of the cache memory. Conceptualization, L.C. ([PERSON]), L.C. ([PERSON]), A.F. and M.P. ; methodology, L.C. ([PERSON]), L.C. ([PERSON]), A.F. and M.P. ; software, M.P. ; validation, A.F., G.G. and M.P. ; formal analysis, G.G. and M.P. ; investigation, G.G. and M.P. ; resources, M.P. ; data curation, M.P. ; writing--original draft preparation, M.P. ; writing--review and editing, L.C. ([PERSON]), L.C. ([PERSON]), A.F., G.G. and M.P. ; visualization, G.G. and M.P. ; supervision, A.F. ; project administration, A.F. ; funding acquisition, A.F. All authors have read and agreed to the published version of the manuscript. This research received no external funding. Data Nanjing StatementData sharing not applicable. No new data were created or analyzed in this study. Data sharing is not applicable to this article. The authors declare no conflict of interest.