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Rencontres sur la Recherche en Informatique R 2 I 2011 12-14 Juin 2011 Tizi-Ouzou, Algérie

Rencontres sur la Recherche en Informatique R 2 I 2011 12-14 Juin 2011 Tizi-Ouzou, Algérie. Empty Answers to Flexible Queries: A Novel Approach. Aicha AGGOUNE 1 , Allel HADJALI 2 1 University of Sétif, Algeria 2 IRISA/ENSSAT, Université de Rennes 1, France . Presented by: .

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Rencontres sur la Recherche en Informatique R 2 I 2011 12-14 Juin 2011 Tizi-Ouzou, Algérie

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  1. Rencontres sur la Recherche en Informatique R2I 2011 12-14 Juin 2011 Tizi-Ouzou, Algérie Empty Answers to Flexible Queries: A Novel Approach Aicha AGGOUNE1, Allel HADJALI2 1University of Sétif, Algeria 2IRISA/ENSSAT, Université de Rennes 1, France Presented by: AGGOUNE Aïcha

  2. 1 2 5 3 4 Content Introduction & Problematic Flexible queries & EAP • Measuring proximity Approaching the EAP Conclusion & perspectives

  3. Introduction & Problematic One of the key elements of the quality of DBMS is the pertinence of the answers, in particular, by the consideration of the preferences of the users in the queries. It  was  shown  that the  theory of  fuzzy  sets  provides  effective tools for expressing preferences. In this case, queries are called the  "Flexible queries (or Fuzzy) ". One of the problems with which the users are confronted, in a process of interrogation, is the problem of the empty answers (EAP). 02/16 • R2I'2011, 12-14 Juin 2011, TiziOuzou, Algérie

  4. Introduction & Problematic The flexible queries limit to a large extent the risk of obtaining of the empty answers, however this risk is not totally eliminated. ? Proposition of a semantic proximity measure between flexible queries for the treatment of the EAP, this measure uses a particular distance, called the Hausdorff distance. 03/16 • R2I'2011, 12-14 Juin 2011, TiziOuzou, Algérie

  5. Flexible queries & EAP Generalization of booleanquery Expression of preferences • Included the vague and impreciseterms Flexible Query • Expression of criteria • importance levels 04/16 • R2I'2011, 12-14 Juin 2011, TiziOuzou, Algérie

  6. Flexible queries & EAP • Simples fuzzypredicates(Cheap, Expensive,…) • Compundfuzzypredicates (Young andWellPaid,…) • FuzzyCriteria • Fuzzypredicates + quantifiers • (plus, less, …) • Fuzzypredicates + modifiers (Very, relatively,…) GradualOperators (Clearlysuperior to) 05/16 • R2I'2011, 12-14 Juin 2011, TiziOuzou, Algérie

  7. Flexible queries & EAP Flexible Query Languages​​: • Extensions of classical interrogations languages​​. • The result of a flexible query is a fuzzy relation for which every tuplet is a degree of membership  noted / t. • Extension of the relational algebra. Ex:  rUs(u)= max(r(u), s(u)) • Threelanguages of type SQL: • SQLF, SQLF Etendu, FQUERY 06/16 • R2I'2011, 12-14 Juin 2011, TiziOuzou, Algérie

  8. Flexible queries & EAP Example: (SQLF) SELECT * FROM VOITURE WHERE Marque = ‘Famous' AND Prix = ‘Cheap'; 07/16 • R2I'2011, 12-14 Juin 2011, TiziOuzou, Algérie

  9. Flexible queries & EAP EmptyAnswersProblem​​: EAP « The problem of empty answers means that all the answers does not inform the user about their questions and satisfy their needs. " Godfrey «A query is said an empty response if it produces no result»  Motro 08/16 • R2I'2011, 12-14 Juin 2011, TiziOuzou, Algérie

  10. Measuring proximity Hausdorff Distance • TheHausdorff distance is a topological tool to deduct the similarity between fuzzy sets, it measures the resemblance or the dissimilarity of two subsets of a metric space. • TheHausdorff distance betweentwo sets A and B is : dH(A, B) = max {supaA infbB d(a, b), supbB infaA d(a, b)} • In the case of a discrete fuzzy set and according to Rosenfeld‘s approach 09/16 • R2I'2011, 12-14 Juin 2011, TiziOuzou, Algérie

  11. Measuring proximity Hausdorff Distance • In the continuous case : • The sementicproximityis: . The simplestformis :   • Ranking  approximate queries is done by  descending order of  • semantic proximity and number of approximate answers. 10/16 • R2I'2011, 12-14 Juin 2011, TiziOuzou, Algérie

  12. Measuring proximity • Single Predicate Queries: • Let Q=P and Q'=P' (P, P' are pertaining to the same attribute A ) : • Compound Queries (more predicates ): • Let Q=P1P2…Pk • There are 3 cases: • Q'=P'1 P'2… P'k(Pi, Pi' are pertaining to the same • attribute Ai)  • Case 2:Q' covers all the attributes specified in Q. • Case 3:Q' does not cover all the attributes specified in Q. • Case 1:Q and Q' cover the same attributes exactly. Q' = P'1 ... P'bP'k+1 … P'swith b < k and(Pi, P'i) D(Ai), for i = 1 to b, predicatsPj(for j = k+1 to s) are not specified in Q. Q'=P'1 ...  P'kP'k+1… P's. • Case 2:Q' covers all the attributes specified in Q. • Case 3:Q' does not cover all the attributes specified in Q. (S1) Increased Q : Q = P1 ...  Pk D(Ak+1 ) …  D(As). Increased Q' :Q' = P'1 ... P'bD(Ab+1)… D(Ak) P'k+1 … P's (S2) Weakening of Q' : Q'R = P'1 ...  P'k . ii. Applying one of two strategies described in case 2. 11/16 • R2I'2011, 12-14 Juin 2011, TiziOuzou, Algérie

  13. Approaching the EAP Principle Using a set of queries previously evaluated by the system and whose answers are not empty (Workload of past queries). • Given the workload, estimating the semantic proximity of the empty answers query Q whith queries of the workload. • The approximate answer to the query is a set of tuples ordered by the closest query in query EA. 12/16 • R2I'2011, 12-14 Juin 2011, TiziOuzou, Algérie

  14. Approaching the EAP Principle Q ∑Q Algorithme TEA Treatment of EAP Q' Q Q Qapp ∑Qapp 13/16 • R2I'2011, 12-14 Juin 2011, TiziOuzou, Algérie

  15. Approaching the EAP Approach • Partitionnons the workload W ( D ) in 03 subsets: • W=(D, Q) = {Q' / Q'  W(D)  |D(Q')  D(Q)| = k}, • W> (D, Q) = {Q' / Q'  W(D)  |D(Q')  D(Q)| > k}, • W< (D, Q) = {Q' / Q'  W(D)  |D(Q')  D(Q)| < k}, 1 • (a)- If W= (D, Q), for element Q' W=(D, Q), estimate the proximityProx(Q, Q'). Ranking in descending order of queries. 2 (b)- Else if W >(D, Q)  , thenweconsider W>(D, Q) and apply (a). (c)- Else, weconsider W<(D, Q) and apply (a). • Choose the closest query Qapp in Q, and affect it as degree of membership, the value of proximity measured Prox (Q, Qapp). 3 14/16 • R2I'2011, 12-14 Juin 2011, TiziOuzou, Algérie

  16. Conclusion & perspectives The main contributions are: The introduction of flexibility on the elements of DB, based on the theory of fuzzy sets; • The proposition of a measure of semanticproximitybetween flexible queries; • Usingthismeasure to treat the EAP. 15/16 • R2I'2011, 12-14 Juin 2011, TiziOuzou, Algérie

  17. Conclusion & perspectives Nevertheless, our approach opens future perspectives. In the short term, the most important are the following ones: • Proposition a search algorithm for closest queries to EA query. • Experiment of the proposed approach. • Analysis of results. • Compare the proposed approach to existing approaches. 16/16 • R2I'2011, 12-14 Juin 2011, TiziOuzou, Algérie

  18. Thank you for your Attention

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