Yazar "Oğuz, Damla" seçeneğine göre listele

Listeleniyor 1 - 1 / 1
  • Küçük Resim
    Öğe
    Optimization methods for large-scale distributed query processing on linked data
    (Ege Üniversitesi, Fen Bilimleri Enstitüsü, 2017) Oğuz, Damla; Bostanoğlu, Ergenç; Hameurlain, Abdelkader
    As the number of Linked Data providers increases, the Web becomes a huge global data space. Query federation is one of the approaches for querying this distributed data space. Query optimization in this approach aims to minimize the response time and the completion time. Response time is the time to generate the first result tuple, whereas completion time refers to the time to provide all result tuples. Most of the studies of query optimization in query federation focus on static query optimization which generates the query plans before the execution and needs statistics. However, the environment of Linked Data has several difficulties such as unpredictable data arrival rates and unreliable statistics. As a consequence, static query optimization can cause inefficient execution plans. These constraints show that adaptive query optimization should be used for federated query processing on Linked Data. In this thesis, we first propose an adaptive join operator which aims to minimize the response time and the completion time for federated queries over SPARQL endpoints. Second, we extend our first proposal to further reduce the completion time. Both proposals can change the join method and the join order during the execution by using adaptive query optimization. The proposed operators can handle different data arrival rates of relations and the lack of statistics about them. The performance evaluation of this thesis shows that the proposed adaptive operators provide the best trade-off between the response time and the completion time. Even though the main objective is to manage different data arrival rates of relations, the performance evaluation reveals that they are successful in both fixed and different data arrival rates.