• Considerations On Low Complexity Codes Concerning Symmetry And Cyclicity 

      Δενδρινός, Μάρκος; Αφράτη, Φώτο; Afrati, Foto; Dendrinos, Markos
      The binary error correcting codes that are examined in this paper are codes which are constructed out of shorter subcodes. The method of construction is well described by a bipartite graph. The one set of nodes of this ...
    • Designing views to efficiently answer real SQL queries 

      Γεργατσούλης, Μανώλης; Αφράτη, Φώτο; Παυλάκη, Βάσια; Chirkova, Rada; Gergatsoulis, Manolis; Afrati, Foto; Pavlaki, Vassia (2005)
      The problem of optimizing queries in the presence of materialized views and the related view-design problem have recently attracted a lot of attention. Significant research results have been reported, and materialized views ...
    • Finding equivalent rewritings in the presence of arithmetic comparisons 

      Γεργατσούλης, Μανώλης; Αφράτη, Φώτο; Chirkova, Rada; Παυλάκη, Βάσια; Afrati, Foto; Pavlaki, Vassia; Gergatsoulis, Manolis (2006)
      The problem of rewriting queries using views has received significant attention because of its applications in a wide variety of data-management problems. For select-project-join SQL (a.k.a. conjunctive) queries and views, ...
    • Linearisability on datalog programs 

      Γεργατσούλης, Μανώλης; Αφράτη, Φώτο; Toni, F.; Gergatsoulis, Manolis; Afrati, Foto (2003)
      Linear Datalog programs are programs whose clauses have at most one intensional atom in their bodies. We explore syntactic classes of Datalog programs (syntactically non-linear) which turn out to express no more than the ...
    • On rewriting Xpath Queries Using Views 

      Γεργατσούλης, Μανώλης; Αφράτη, Φώτο; Chirkova, Rada; Kimelfeld, B.; Παυλάκη, Βάσια; Sagiv, Y.; Gergatsoulis, Manolis; Afrati, Foto; Pavlaki, Vassia (2009)
      The problem of rewriting a query using a materialized view is studied for a well known fragment of XPath that includes the following three constructs: wildcards, descendant edges and branches. In earlier work, determining ...
    • On solving efficiently the view selection problem under bag-semantics 

      Γεργατσούλης, Μανώλης; Αφράτη, Φώτο; Damigos, M.; Gergatsoulis, Manolis; Afrati, Foto (2009)
      In this paper, we investigate the problem of view selection for workloads of conjunctive queries under bag semantics. In particular we aim to limit the search space of candidate viewsets. In that respect we start delineating ...
    • Query containment under bag and bag-set semantics 

      Γεργατσούλης, Μανώλης; Αφράτη, Φώτο; Damigos, M.; Gergatsoulis, Manolis; Afrati, Foto (2010)
      Conjunctive queries (CQs) are at the core of query languages encountered in many logic-based research fields such as AI, or database systems. The majority of existing work assumes set semantics but often in real applications ...
    • Union rewritings for XPath fragments 

      Γεργατσούλης, Μανώλης; Αφράτη, Φώτο; Damigos, M.; Gergatsoulis, Manolis; Afrati, Foto (2011)
      In this paper, we study the problem of finding an equivalent rewriting of an XPath query using multiple views, and we show that the union operator may be required in order to find such a rewriting. In particular, focusing ...
    • View selection for real conjunctive queries 

      Αφράτη, Φώτο; Chirkova, Rada; Γεργατσούλης, Μανώλης; Παυλάκη, Βάσια; Afrati, Foto; Gergatsoulis, Manolis; Pavlaki, Vassia (2007)
      Given a query workload, a database and a set of constraints, the view-selection problem is to select views to materialize so that the constraints are satisfied and the views can be used to compute the queries in the ...