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Formal Availability Analysis using Theorem Proving [article]

Waqar Ahmed, Osman Hasan
2016 arXiv   pre-print
Availability analysis is used to assess the possible failures and their restoration process for a given system. This analysis involves the calculation of instantaneous and steady-state availabilities of the individual system components and the usage of this information along with the commonly used availability modeling techniques, such as Availability Block Diagrams (ABD) and Fault Trees (FTs) to determine the system-level availability. Traditionally, availability analyses are conducted using
more » ... per-and-pencil methods and simulation tools but they cannot ascertain absolute correctness due to their inaccuracy limitations. As a complementary approach, we propose to use the higher-order-logic theorem prover HOL4 to conduct the availability analysis of safety-critical systems. For this purpose, we present a higher-order-logic formalization of instantaneous and steady-state availability, ABD configurations and generic unavailability FT gates. For illustration purposes, these formalizations are utilized to conduct formal availability analysis of a satellite solar array, which is used as the main source of power for the Dong Fang Hong-3 (DFH-3) satellite.
arXiv:1608.01755v1 fatcat:5k6o24jwsvfj7kkf7qne5wfm2e

Towards Formal Fault Tree Analysis using Theorem Proving [article]

Waqar Ahmed, Osman Hasan
2015 arXiv   pre-print
Fault Tree Analysis (FTA) is a dependability analysis technique that has been widely used to predict reliability, availability and safety of many complex engineering systems. Traditionally, these FTA-based analyses are done using paper-and-pencil proof methods or computer simulations, which cannot ascertain absolute correctness due to their inherent limitations. As a complementary approach, we propose to use the higher-order-logic theorem prover HOL4 to conduct the FTA-based analysis of
more » ... ritical systems where accuracy of failure analysis is a dire need. In particular, the paper presents a higher-order-logic formalization of generic Fault Tree gates, i.e., AND, OR, NAND, NOR, XOR and NOT and the formal verification of their failure probability expressions. Moreover, we have formally verified the generic probabilistic inclusion-exclusion principle, which is one of the foremost requirements for conducting the FTA-based failure analysis of any given system. For illustration purposes, we conduct the FTA-based failure analysis of a solar array that is used as the main source of power for the Dong Fang Hong-3 (DFH-3) satellite.
arXiv:1505.02648v1 fatcat:7ulnrqywubcr3merkju53dfppe

Shorter Notices

Ahmad Waqar Qasim, (Lubna Hasan
2012 Pakistan Development Review  
(Lubna Hasan). Asia-The Way Forward. Sustainable Development Policy Institute and Sang-e-Meel Publications. 2012. Hard Cover. 305 pages. Rs 1200.00.  ... 
doi:10.30541/v51i1pp.101-102 fatcat:pqmjzlsdizhpdf5qx2k5sjigna

Formal Dependability Modeling and Analysis: A Survey [article]

Waqar Ahmed, Osman Hasan, Sofiene Tahar
2016 arXiv   pre-print
Dependability is an umbrella concept that subsumes many key properties about a system, including reliability, maintainability, safety, availability, confidentiality, and integrity. Various dependability modeling techniques have been developed to effectively capture the failure characteristics of systems over time. Traditionally, dependability models are analyzed using paper-and-pencil proof methods and computer based simulation tools but their results cannot be trusted due to their inherent
more » ... curacy limitations. The recent developments in probabilistic analysis support using formal methods have enabled the possibility of accurate and rigorous dependability analysis. Thus, the usage of formal methods for dependability analysis is widely advocated for safety-critical domains, such as transportation, aerospace and health. Given the complementary strengths of mainstream formal methods, like theorem proving and model checking, and the variety of dependability models judging the most suitable formal technique for a given dependability model is not a straightforward task. In this paper, we present a comprehensive review of existing formal dependability analysis techniques along with their pros and cons for handling a particular dependability model.
arXiv:1606.06877v1 fatcat:kbirvfq6g5eyzf5jfauewlg6bu

Query optimization for parallel execution

Sumit Ganguly, Waqar Hasan, Ravi Krishnamurthy
1992 SIGMOD record  
The decreasing cost of computing makes
doi:10.1145/141484.130291 fatcat:h5g3wv5p3bgpdogtkq5xdmqpkm

Formal Probabilistic Analysis of Dynamic Fault Trees in HOL4 [article]

Yassmeen Elderhalli, Waqar Ahmad, Osman Hasan, Sofiene Tahar
2018 arXiv   pre-print
Dynamic Fault Trees (DFTs) is a widely used failure modeling technique that allows capturing the dynamic failure characteristics of systems in a very effective manner. Simulation and model checking have been traditionally used for the probabilistic analysis of DFTs. Simulation is usually based on sampling and thus its results are not guaranteed to be complete, whereas model checking employs computer arithmetic and numerical algorithms to compute the exact values of probabilities, which contain
more » ... any round-off errors. Leveraging upon the expressive and sound nature of higher-order-logic (HOL) theorem proving, we propose, in this work, a formalization of DFT gates and their probabilistic behavior as well as some of their simplification properties in HOL. This formalization would allow us to conduct the probabilistic analysis of DFTs by verifying generic mathematical expressions about their behavior in HOL. In particular, we formalize the AND, OR, Priority-AND, Functional DEPendency, Hot SPare, Cold SPare and the Warm SPare gates and also verify their corresponding probabilistic expressions in HOL. Moreover, we formally verify an important property, Pr(X<Y), using the Lebesgue integral as this relationship allows us to reason about the probabilistic properties of Priority-AND gate and the Before operator. We also formalize the notion of conditional densities in order to formally verify the probabilistic expressions of the Cold SPare and the Warm SPare gates. For illustrating the usefulness of our formalization, we use it to formally analyze the DFT of a Cardiac Assist System.
arXiv:1807.11576v1 fatcat:gmogifu3w5ee7eblafm27oyvrq

Open issues in parallel query optimization

Waqar Hasan, Daniela Florescu, Patrick Valduriez
1996 SIGMOD record  
We provide an overview of query processing in parallel database systems and discuss several open issues in the optimization of queries for parallel machines. DANIELA FLORESCU INRIA, France Daniela.Florescu @ Introduction Parallel database systems combine data management and parallel processing techniques to provide highperformance, high-availability and scalability for dataintensive applications [10, 35] . By exploiting parallel computers, they provide performance at a cheaper price
more » ... n traditional mainframe solutions. Further, they are the solution of choice for high transaction throughput in OLTP systems as well as low response times in decisionsupport systems. Finally, parallel databases are the only viable solution for very large databases. SQL, the standard language for programming database access, is a high-level, set-oriented, declarative language. This permits SQL compilers to automatically infer and exploit parallelism. Users do not have to learn a new language and application code does not need to be rewritten to benefit from parallel execution. This is to be contrasted to the use of lower-level languages in scientific computing which often requires re-writing application code to take advantage of parallel machines. A key to the success of parallel database systems, particularly in decision-support applications, is parallel query optimization. Given a SQL query, parallel query optimization has the goal of finding a parallel plan that delivers the query result in minimal time. While considerable progress has been made, several problems remain open. Further, solutions to the optimization problem are sensitive to the query language expressive power, the underlying execution mechanisms, the machine architecture, and variations in the cost metric being minimized. New applications, demands for higher performance from existing applications, innovations in query execution mechanisms and machine architectures are changing some of the underlying assumptions thereby offering new challenges. Parallel query optimization offers challenges beyond those addressed by past research in fields such as distributed databases [30] or classical scheduling theory [18] . While distributed and parallel databases are fundamentally similar, research in distributed query optimization was done in the early 1980s, a time at which *Current address: Informix Soft'are.
doi:10.1145/234889.234894 fatcat:kbvsxwxmxnhetg5adb47hx6bna

Formalization of Fault Trees in Higher-order Logic: A Deep Embedding Approach [article]

Waqar Ahmed, Osman Hasan
2016 arXiv   pre-print
Fault Tree (FT) is a standard failure modeling technique that has been extensively used to predict reliability, availability and safety of many complex engineering systems. In order to facilitate the formal analysis of FT based analyses, a higher-order-logic formalization of FTs has been recently proposed. However, this formalization is quite limited in terms of handling large systems and transformation of FT models into their corresponding Reliability Block Diagram (RBD) structures, i.e., a
more » ... quently used transformation in reliability and availability analyses. In order to overcome these limitations, we present a deep embedding based formalization of FTs. In particular, the paper presents a formalization of AND, OR and NOT FT gates, which are in turn used to formalize other commonly used FT gates, i.e., NAND, NOR, XOR, Inhibit, Comparator and majority Voting, and the formal verification of their failure probability expressions. For illustration purposes, we present a formal failure analysis of a communication gateway software for the next generation air traffic management system.
arXiv:1608.06392v1 fatcat:xaigfcnec5dp7m5vgzdmmsxt64

On the Formalization of Importance Measures using HOL Theorem Proving [article]

Waqar Ahmed, Shahid Ali Murtza, Osman Hasan, Sofiene Tahar
2019 arXiv   pre-print
Importance measures provide a systematic approach to scrutinize critical system components, which are extremely beneficial in making important decisions, such as prioritizing reliability improvement activities, identifying weak-links and effective usage of given resources. The importance measures are then in turn used to obtain a criticality value for each system component and to rank the components in descending manner. Simulations tools are generally used to perform importance measure based
more » ... alysis, but they require expensive computations and thus they are not suitable for large systems. A more scalable approach is to utilize the importance measures to obtain all the necessary conditions by proving a generic relationship describing the relative importance between any pair of components in a system. In this paper, we propose to use higher-order-logic (HOL) theorem proving to verify such relationships and thus making sure that all the essential conditions are accompanied by the proven property. In particular, we formalize the commonly used importance measures, such as Birnbaum and Fussell-Vesely, and conduct a formal importance measure analysis of a railway signaling system at a Moroccan level crossing as an application for illustration purpose.
arXiv:1904.01605v1 fatcat:3dydxhzjzvaepoxh3jgpkvvdg4

Coloring Away Communication in Parallel Query Optimization

Waqar Hasan, Rajeev Motwani
1995 Very Large Data Bases Conference  
trees that minimize the computation and communication costs of parallel execution. We address the problem of finding parallel plans for SQL queries using the two-phase approach of join ordering and query rewrite (JOQR) followed by parallelization. We focus on the JOQR phase and develop optimization algorithms that account for communication as well as computation costs. Using a model based on representing the partitioning of data as a color, we devise an efficient algorithm for the problem of
more » ... osing the partitioning attributes in a query tree so as to minimize total cost. We extend our model and algorithm to incorporate the interaction of data partitioning with conventional optimization choices such as access methods and strategies for computing operators. Our algorithms apply to queries that include operators such as grouping, aggregation, intersection and set difference in addition to joins.
dblp:conf/vldb/HasanM95 fatcat:esxltajio5duhews3kvivvamca

Extensible/rule based query rewrite optimization in Starburst

Hamid Pirahesh, Joseph M. Hellerstein, Waqar Hasan
1992 SIGMOD record  
This paper describes the Query Rewrite facility of the Starburst extensible database system, a novel phase of query optimization. We present a suite of rewrite rules used in Starburst to transform queries into equivalent queries for faster execution, and also describe the production rule engine which is used by Starburst to choose and execute these rules. Examples we provided demonstrating that these Query Rewrite transformations lead to query execution time improvements of orders of magnitude,
more » ... suggesting that Query Rewrite in general -and these rewrite rules in particular -are an essential step in query optimization for modern database systems.
doi:10.1145/141484.130294 fatcat:22b22gtjzrcjxmr24foukkkqbm

Dynamic Fault Trees Analysis using an Integration of Theorem Proving and Model Checking [article]

Yassmeen Elderhalli, Osman Hasan, Waqar Ahmad, Sofiene Tahar
2017 arXiv   pre-print
Dynamic fault trees (DFTs) have emerged as an important tool for capturing the dynamic behavior of system failure. These DFTs are then analyzed qualitatively and quantitatively using stochastic or algebraic methods to judge the failure characteristics of the given system in terms of the failures of its sub-components. Model checking has been recently proposed to conduct the failure analysis of systems using DFTs with the motivation to provide a rigorous failure analysis of safety-critical
more » ... s. However, model checking has not been used for the DFT qualitative analysis and the reduction algorithms used in model checking are usually not formally verified. Moreover, the analysis time grows exponentially with the increase of the number of states. These issues limit the usefulness of model checking for analyzing complex systems used in safety-critical domains, where the accuracy and completeness of analysis matters the most. To overcome these limitations, we propose a comprehensive methodology to perform the qualitative and quantitative analysis of DFTs using an integration of theorem proving and model checking based approaches. For this purpose, we formalized all the basic dynamic fault tree gates using higher-order logic based on the algebraic approach and formally verified some of the simplification properties. This formalization allows us to formally verify the equivalence between the original and reduced DFTs using a theorem prover, and conduct the qualitative analysis. We then use model checking to perform the quantitative analysis of the formally verified reduced DFT. We applied our methodology to five benchmarks and the results show that the formally verified reduced DFT was analyzed using model checking with up to six times less states and up to 133000 times faster.
arXiv:1712.02872v1 fatcat:xxpxgog3cnevfazych5hs5iliy

Query optimization for parallel execution

Sumit Ganguly, Waqar Hasan, Ravi Krishnamurthy
1992 Proceedings of the 1992 ACM SIGMOD international conference on Management of data - SIGMOD '92  
The decreasing cost of computing makes
doi:10.1145/130283.130291 dblp:conf/sigmod/GangulyHK92 fatcat:vqnpe5h6lbbnfdnmp3gbij5udm

Column Behavior of Cold‐Formed Hollow Sections

Peter W. Key, Syed Waqar Hasan, Gregory J. Hancock
1988 Journal of Structural Engineering  
The results of an experimental investigation into the strength and collapse behaviour of Australian produced cold-formed square and rectangular hollow section columns is described. The individual plate strengths calculated from the stub column tests on both square and rectangular hollow sections are compared with predictions based on the effective width formulae in the AISI Specification. The long column test results on square hollow sections are compared with the AISI Class A and Class B
more » ... curves as well as a proposal based on the SSRC mUltiple column curves. The sections studied had plate width to thickness ratios in a range where local buckling and yielding occur almost simultaneously, leading to rapid load shedding after ultimate. Theoretical models of the post-ultimate collapse behaviour, based on local plastic mechanisms, are summarised in the paper. The theoretical models are compared with the collapse behaviour of the stub columns and long columns.
doi:10.1061/(asce)0733-9445(1988)114:2(390) fatcat:psz23gfairbkzjoxiy7hxupbni

Development And Calibration Of A Portable Controller For Adjustable Pulmonary Artery Shunt

Muhammad Z Hasan, Eduardo Beattie, John Witt, Waqar Mohiuddin, Rainer Fink
2018 Zenodo  
Control of Pulmonary Blood Flow (PBF) in newborn babies remains challenging after surgery for congenital heart disorders. According to multi-institutional data, the mortality after this complex surgery is 15%-20%. A leading cause of high mortality is the difficulty in maintaining balance between blood flowing into the body and the lungs. Control of flow can be improved with medical therapies that have unwanted side effects. As such, a mechanical blood flow control device is preferable. A
more » ... l Computer (PC) based system is used at present that has issues of size and portability. Design and calibration of a smaller, portable version of the controller is desired and a 90% smaller controller is presented in this paper. Experimental results show that the controller can vary flow rate from 100% (fully open switch) to 20% (fully closed switch). A consistent flow rate is obtained using such a controller with minimal deviations from the desired flow (as low as 0.36%). This very specialized heart disorder condition occurs in about 1000 patients annually. As such, commercial companies find little motivation for investment and the obligation lies on non-profit institutions to take up such an initiative.
doi:10.5281/zenodo.1419825 fatcat:xsobf4wdnzfk5ai2hho5icf6a4
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