Computer Engineering / Bilgisayar Mühendisliği

Permanent URI for this collectionhttps://hdl.handle.net/11147/10

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Now showing 1 - 8 of 8
  • Article
    Citation - WoS: 23
    Citation - Scopus: 31
    A Survey on Multithreading Alternatives for Soft Error Fault Tolerance
    (Association for Computing Machinery (ACM), 2019) Öz, Işıl; Arslan, Sanem
    Smaller 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: 41
    Effort 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, Onur
    Agile 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: 5
    Effort Estimation Methods for Erp Projects Based on Function Points: a Case Study
    (Association for Computing Machinery (ACM), 2017) Küçükateş Ömüral, Neslihan; Demirörs, Onur
    Enterprise 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: 2
    Comparison of Dynamic Itemset Mining Algorithms for Multiple Support Thresholds
    (Association for Computing Machinery (ACM), 2017) Abuzayed, Nourhan; Ergenç, Belgin
    Mining1 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
    Citation - Scopus: 2
    Resource Allocation Algorithm for a Relational Join Operator in Grid Systems
    (Association for Computing Machinery (ACM), 2012) Çokuslu, Deniz; Hameurlain, Abdelkader; Erciyeş, Kayhan; Morvan, Franck
    Grid 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: 1
    Reading Cs Classics
    (Association for Computing Machinery (ACM), 2012) Tekir, Selma
    Knowledge 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.
  • Report
    Implementing Fault-Tolerance in Real-Time Systems by Automatic Program Transformations
    (Association for Computing Machinery (ACM), 2006) Ayav, Tolga; Fradet, Pascal; Girault, Alain
    We 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.
  • Article
    Citation - WoS: 6
    Citation - Scopus: 9
    Implementing Fault-Tolerance in Real-Time Programs by Automatic Program Transformations
    (Association for Computing Machinery (ACM), 2008) Ayav, Tolga; Fradet, Pascal; Girault, Alain
    We present a formal approach to implement fault-tolerance in real-time embedded systems. The initial fault-intolerant system consists of a set of independent periodic tasks scheduled onto a set of fail-silent processors connected by a reliable communication network. 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 rollback. These techniques are described and implemented by automatic program transformations on the tasks' programs. The proposed formal approach to fault-tolerance by program transformations highlights the benefits of separation of concerns. It allows us to establish correctness properties and to compute optimal values of parameters to minimize fault-tolerance overhead. We also present an implementation of our method, to demonstrate its feasibility and its efficiency.