Scopus İndeksli Yayınlar Koleksiyonu / Scopus Indexed Publications Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7148
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Article Citation - WoS: 23Citation - Scopus: 31A Survey on Multithreading Alternatives for Soft Error Fault Tolerance(Association for Computing Machinery (ACM), 2019) Öz, Işıl; Arslan, SanemSmaller transistor sizes and reduction in voltage levels in modern microprocessors induce higher soft error rates. This trend makes reliability a primary design constraint for computer systems. Redundant multithreading (RMT) makes use of parallelism in modern systems by employing thread-level time redundancy for fault detection and recovery. RMT can detect faults by running identical copies of the program as separate threads in parallel execution units with identical inputs and comparing their outputs. In this article, we present a survey of RMT implementations at different architectural levels with several design considerations. We explain the implementations in seminal papers and their extensions and discuss the design choices employed by the techniques. We review both hardware and software approaches by presenting the main characteristics and analyze the studies with different design choices regarding their strengths and weaknesses. We also present a classification to help potential users find a suitable method for their requirement and to guide researchers planning to work on this area by providing insights into the future trend.Conference Object Citation - Scopus: 41Effort Estimation for Agile Software Development: Comparative Case Studies Using Cosmic Functional Size Measurement and Story Points(Association for Computing Machinery (ACM), 2017) Salmanoğlu, Murat; Hacaloğlu, Tuna; Demirörs, OnurAgile methodologies have gained significant popularity among software development organizations during the last decade. Although agile methodologies are regarded as minimizing formal processes, they still utilize an estimation methodology for proper management. Story point is the most common input for agile effort estimation. Story point is an arbitrary measure; it reflects experiences of project participants. On the other hand, functional size is an alternative measure used in practice as an input for effort estimation. In this research, we collect and present the outcomes of three case studies which compared the effectiveness of COSMIC-based and story point based effort estimation in agile context. On selected projects of these organizations, software functional size was measured with COSMIC functional size measurement methodology. Effort prediction models were formed by using COSMIC size and actual effort spent; and the models were tested in terms of their effectiveness. The results show controversial outcomes. For all the cases, COSMIC based estimation was more precise. Therefore, COSMIC is an appropriate measure to estimate the effort in organizations that adopt agile software development. It is also observed that COSMIC allowed for computing productivity which has less disperse distribution than the productivity computed with SP. The data is also provided to help other researchers conduct their own studies.Conference Object Citation - Scopus: 5Effort Estimation Methods for Erp Projects Based on Function Points: a Case Study(Association for Computing Machinery (ACM), 2017) Küçükateş Ömüral, Neslihan; Demirörs, OnurEnterprise Resource Planning (ERP) Systems evolve at a rapid pace based on customer and industry expectations. As a result, historic project data for these kinds of projects lose their value especially for analogy based estimation methods. In this rapidly evolving domain, function point based methods might provide a sound alternative for ERP effort estimation. This paper presents the results obtained by applying three methods published in the literature in which function points are used as an input for ERP effort estimation. The evaluation of these methods with respect to their measurement processes and estimation errors are presented; their advantages and disadvantages are discussed.Conference Object Citation - Scopus: 2Comparison of Dynamic Itemset Mining Algorithms for Multiple Support Thresholds(Association for Computing Machinery (ACM), 2017) Abuzayed, Nourhan; Ergenç, BelginMining1 frequent itemsets is an important part of association rule mining process. Handling dynamic aspect of databases and multiple support threshold requirements of items are two important challenges of frequent itemset mining algorithms. Most of the existing dynamic itemset mining algorithms are devised for single support threshold whereas multiple support threshold algorithms are static. This work focuses on dynamic update problem of frequent itemsets under multiple support thresholds and proposes tree-based Dynamic CFP-Growth++ algorithm. Proposed algorithm is compared to our previous dynamic algorithm Dynamic MIS [50] and a recent static algorithm CFP-Growth++ [2] and, findings are; in dynamic database, 1) both of the dynamic algorithms are better than the static algorithm CFP-Growth++, 2) as memory usage performance; Dynamic CFP-Growth++ performs better than Dynamic MIS, 3) as execution time performance; Dynamic MIS is better than Dynamic CFP-Growth++. In short, Dynamic CFP-Growth++ and Dynamic MIS have a trade-off relationship in terms of memory usage and execution time.Conference Object Effect of Traffic Arrival Distributions on Routing Strategy in Multi-Hop Wireless Networks(Association for Computing Machinery (ACM), 2016) Aydoğdu, CananThe basic problem of whether direct transmission or multi- hop routing increases goodput in multi-hop wireless net- works still lacks investigation from many aspects. This ar- ticle, approaches this problem by considering the effect of different traffic arrival distributions on the choice of rout- ing strategy for enhancing goodput of IEEE 802.11 DCF based multi-hop wireless networks under hidden terminal existence. Different traffic arrival distributions including Poisson, constant bit rate (CBR), Pareto and Exponential are considered, relaxing the generally adopted Poisson as- sumption, for various data rates over a wide range of traffic loads extending from unsaturated to saturated traffic loads. The goodput performance for all traffic arrival distribu- tions is found to be dependent on the traffic load in multi- hop networks. Of the four traffic models used, the network achieved the best goodput with Pareto and Exponential ar- rival distributions for light traffic loads, where CBR per- forms slightly better under heavy loads. The results suggest that a traffic load-aware pre-control mechanism on the traffic arrivals to the IEEE 802.11 MAC layer might provide signicant goodput gains in multi-hop wireless networks.Conference Object Citation - Scopus: 2Resource Allocation Algorithm for a Relational Join Operator in Grid Systems(Association for Computing Machinery (ACM), 2012) Çokuslu, Deniz; Hameurlain, Abdelkader; Erciyeş, Kayhan; Morvan, FranckGrid systems become very popular during the last decade because of their rapidly increasing computational capabilities. On the other hand, the advances on different domains cause enormous increase in the scale of the manipulated data. This issue augments the importance of distributed query processing and causes researchers to port their underlying environment onto the grid systems. However the dynamicity, heterogeneity and large scale characteristics of grid systems pose new problems for the distributed query processing domain. Resource allocation for query processing in grid systems is one of these problems, which attracts many researchers' attention. In this paper, we propose a new resource allocation algorithm for one relational join operator in a query considering characteristics of the grid systems. We provide theoretical analyses of the proposed algorithm and we consolidate analyses with the simulations. Copyright © 2012 ACM.Article Citation - WoS: 1Reading Cs Classics(Association for Computing Machinery (ACM), 2012) Tekir, SelmaKnowledge of the theories of computer science (CS) helps in understanding the limitations of the field by providing users with new perspectives and insights. It can be a good practice for CS professionals to compile their own list of classics that highlights some key scientific concepts of the field. 'An Axiomatic Basis for Computer Programming,' by C.A.R. Hoare is a CS classic, which tells about the computing industry of the 1960s and 1970s in Britain. Hoare provides a foundation for the formal proofs of programs by an algebraic assertions-based approach. 'Computing Machinery and Intelligence,' by A.M. Turing tells about the computer numbering systems that provide unique representation to every programming construct. Dijkstra' s realization of the high intellectual challenge of programming and his encouragement made him one of the greatest minds of computer programming. Donald Knuth is extraordinary with his perspective on computer programming.Conference Object Citation - WoS: 22Multi-Party Off-The Messaging(Association for Computing Machinery (ACM), 2009) Goldberg, Ian; Ustaoğlu, Berkant; Van Gundy, Matthew D.; Chen, HaoMost cryptographic algorithms provide a means for secret and authentic communication. However, under many circumstances, the ability to repudiate messages or deny a conversation is no less important than secrecy and authenticity. For whistleblowers, informants, political dissidents and journalists - to name a few - it is most important to have means for deniable conversation, where electronic communication must mimic face-to-face private meetings. Off-the-Record Messaging, proposed in 2004 by Borisov, Goldberg and Brewer, and its subsequent improvements, simulate private two-party meetings. Despite some attempts, the multi-party scenario remains unresolved. In this paper, we first identify the properties of multi-party private meetings. We illustrate the differences not only between the physical and electronic medium but also between two- and multi-party scenarios, which have important implications for the design of private chatrooms. We then propose a solution to multi-party off-the-record instant messaging that satisfies the above properties. Our solution is also composable with extensions that provide other properties, such as anonymity. Copyright 2009 ACM.Conference Object Security Arguments for the Um Key Agreement Protocol in the Nist Sp 800-56a Standard(Association for Computing Machinery (ACM), 2008) Menezes, Alfred; Ustaoğlu, BerkantThe Unified Model (UM) key agreement protocol is an efficient Diffie-Hellman scheme that has been included in many cryptographic standards, most recently in the NIST SP 800-56A standard. The UM protocol is believed to possess all important security attributes including key authentication and secrecy, resistance to unknown key-share attacks, forward secrecy, resistance to known-session key attacks, and resistance to leakage of ephemeral private keys, but is known to succumb to key-compromise impersonation attacks. In this paper we present a strengthening of the Canetti-Krawczyk security definition for key agreement that captures resistance to all important attacks that have been identified in the literature with the exception of key-compromise impersonation attacks. We then present a reductionist security proof that the UM protocol satisfies this new definition in the random oracle model under the Gap Diffie-Hellman assumption. Copyright 2008 ACM.Report Implementing Fault-Tolerance in Real-Time Systems by Automatic Program Transformations(Association for Computing Machinery (ACM), 2006) Ayav, Tolga; Fradet, Pascal; Girault, AlainWe present a formal approach to implement and certify fault-tolerance in real-time embedded systems. The fault-intolerant initial system consists of a set of independent periodic tasks scheduled onto a set of fail-silent processors. We transform the tasks such that, assuming the availability of an additional spare processor, the system tolerates one failure at a time (transient or permanent). Failure detection is implemented using heartbeating, and failure masking using checkpointing and roll-back. These techniques are described and implemented by automatic program transformations on the tasks' programs. The proposed formal approach to fault-tolerance by program transformation highlights the benefits of separation of concerns and allows us to establish correctness properties.