Computer Engineering / Bilgisayar Mühendisliği
Permanent URI for this collectionhttps://hdl.handle.net/11147/10
Browse
3 results
Search Results
Article Citation - WoS: 4Citation - Scopus: 5Query optimization: Mobile agents versus accuracy of the cost estimation(CRL Publishing, 2005) Özakar, Belgin; Morvan, F.; Hameurlaint, A.Since an increasing number of diverse sources of data and information become available through World Wide Web, the field of distributed heterogeneous query processing attracts attention of the researchers. One of the main concerns is to reduce the amount of communication and the volume of data transferred in terms of query optimization where it is a real challenge to have the statistics of the resources predictable and up-to-date. Autonomy, proactivity and mobility features of mobile agents seem promising under some conditions. In this paper we are interested in the study of the efficiency of the mobile agents in relation with the approach of the cost model used during the optimization process. We present an execution model based on mobile agents. Performance evaluation shows the efficiency intervals of the execution model according to the estimation errors and the current state of the system. The major contribution of this paper is to point out the effective use of an execution model based on mobile agents in relation with the approach of the cost model and with the query type. © 2005 CRL Publishing Ltd.Conference Object Citation - Scopus: 9Event-Based Input Validation Using Design-By Patterns(Institute of Electrical and Electronics Engineers Inc., 2009) Tuğlular, Tuğkan; Müftüoğlu, Can Arda; Belli, Fevzi; Linschulte, M.This paper proposes an approach for validation of numerical inputs based on graphical user interfaces (GUI) that are modeled and specified by event sequence graphs (ESG). For considering complex structures of input data, ESGs are augmented by decision tables and patterns of design by contract (DbC). The approach is evaluated by experiments on boundary overflows, which occur when input values violate the range of specified values. Furthermore, a tool is presented that implements our approach enabling a semiautomatically detection of boundary overflow errors and suggesting correction steps based on DbC.Article Citation - WoS: 6Citation - Scopus: 9Implementing Fault-Tolerance in Real-Time Programs by Automatic Program Transformations(Association for Computing Machinery (ACM), 2008) Ayav, Tolga; Fradet, Pascal; Girault, AlainWe 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.