Sürdürülebilir Yeşil Kampüs Koleksiyonu / Sustainable Green Campus Collection
Permanent URI for this collectionhttps://hdl.handle.net/11147/7755
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Article Citation - WoS: 17Citation - Scopus: 26Federated Query Processing on Linked Data: a Qualitative Survey and Open Challenges(Cambridge University Press, 2015) Oğuz, Damla; Ergenç, Belgin; Yin, Shaoyi; Dikenelli, Oğuz; Hameurlain, AbdelkaderA large number of data providers publish and connect their structured data on the Web as linked data. Thus, the Web of data becomes a global data space. In this paper, we initially give an overview of query processing approaches used in this interlinked and distributed environment, and then focus on federated query processing on linked data. We provide a detailed and clear insight on data source selection, join methods and query optimization methods of existing query federation engines. Furthermore, we present a qualitative comparison of these engines and give a complementary comparison of the measured metrics of each engine with the idea of pointing out the major strengths of each one. Finally, we discuss the major challenges of federated query processing on linked data. © 2015 Cambridge University Press.Conference Object Citation - Scopus: 7Orderbased Labeling Scheme for Dynamic Xml Query Processing(Springer Verlag, 2012) Assefa, Beakal Gizachew; Ergenç, BelginNeed for robust and high performance XML database systems increased due to growing XML data produced by today's applications. Like indexes in relational databases, XML labeling is the key to XML querying. Assigning unique labels to nodes of a dynamic XML tree in which the labels encode all structural relationships between the nodes is a challenging problem. Early labeling schemes designed for static XML document generate short labels; however, their performance degrades in update intensive environments due to the need for relabeling. On the other hand, dynamic labeling schemes achieve dynamicity at the cost of large label size or complexity which results in poor query performance. This paper presents OrderBased labeling scheme which is dynamic, simple and compact yet able to identify structural relationships among nodes. A set of performance tests show promising labeling, querying, update performance and optimum label size. © 2012 IFIP International Federation for Information Processing.Conference Object Citation - WoS: 4Citation - Scopus: 6Robust Placement of Mobile Relational Operators for Large Scale Distributed Query Optimization(Institute of Electrical and Electronics Engineers Inc., 2007) Ergenç, Belgin; Morvan, Franck; Hameurlain, AbdelkaderThis paper presents a compile-time placement method of mobile relational operators MROs in a large scale environment. MROs are self adaptive to changing runtime conditions by deciding their execution place if they discover compile-time estimation errors. Proposed placement methods tend to have a main drawback with MROs running over a large scale environment: their focus is on finding optimal performance depending on single-point estimation at compile-time, instead of optimal performance over an estimation interval. We propose: (i) to determine the migration space of a MRO including the sites on which the MRO is allowed to migrate during its execution, and (ii) to find the robust site which will allow acceptable response time in an estimation interval. Performance study shows that, with a risk of loosing around 6% in response time, it is possible to gain up to 300% with the proposed robust placement.Master Thesis Distinct Encoded Records Join Operator for Distributed Query Processing(Izmir Institute of Technology, 2012) Öztürk, Ahmet Cumhur; Ergenç, BelginNowadays distributing data among different locations is very popular due to needs of business environment. In today's business environment, accessible, reliable, and scalable data is a critical need and distributed database system provides those advantages. It is a need to transfer data between sites while processing query in distributed database system, if the connection speed between sites is low then transmitting data is very time consuming. Optimizing distributed query processing is different from optimizing query processing in local database system. Most of the algorithms generated for distributed query processing focus on reducing the amount of data transferred between sites. Join operation in database system is for combining different tables with a common join attribute value, if the tables that are put in a join operation are at different locations then some of the tables are needed to be transferred to between sites. Join operation optimization algorithms in distributed database system focus on reducing the amount of data transfer by eliminating redundant tuples from relation before transmitting it to the other site. This thesis introduces a new distributed query processing technique named distinct encoded records join operation (DERjoin) which considers duplicated join attributes in a relation and eliminates them before sending the relation to another site.