When: Friday, July 4, at 14.00

Where: PCRI building, room 445

Who: Ioana Ileana

Title: Complete Yet Practical Search For Minimal Query Reformulations Under Constraints

Abstract:
We revisit the Chase & Backchase algorithm for query reformulations under constraints. For an important class of queries and constraints, C&B has been shown to be complete, i.e. guaranteed to find all (join-)minimal reformulations under constraints. C & B is based on constructing a canonical rewriting candidate called a universal plan, then inspecting its exponentially many sub-queries in search for minimal reformulations, essentially removing redundant joins in all possible ways. This inspection involves chasing the subquery. Because of the resulting exponentially many chases, the conventional wisdom has held that completeness is a concept of mainly theoretical interest.

We show that completeness can be preserved at practically relevant cost by introducing Provenance-Aware Chase & Backchase, a novel reformulation algorithm that instruments the chase to maintain provenance information connecting the joins added during the chase to the universal plan subqueries responsible for adding these joins. This allows it to directly “read off” the minimal reformulations from the result of a single chase of the universal plan, saving exponentially many chases of its subqueries. We exhibit natural scenarios yielding speedups of over two orders of magnitude between the execution of the best view-based rewriting found by a commercial query optimizer and that of the best rewriting found by Prov C&B (which the optimizer misses because of limited reasoning about constraints).”

Joint work with Bogdan Cautis, Alin Deutsch, and Yannis Katsis.

When: Friday, May 23, at 14.00

Where: PCRI building, room 455

Who: Gianluca Quercini, Supélec

Title: Matching User Profiles across Social Networks

Abstract:
Social Networking Sites, such as Facebook and LinkedIn, are clear examples of the impact that the Web 2.0 has on people around the world, because they target an aspect of life that is extremely important to anyone: social relationships. The key to building a social network is the ability of finding people that we know in real life, which, in turn, requires those people to make publicly available some personal information, such as their names, family names, locations and birth dates, just to name a few. However, it is not uncommon that individuals create multiple profiles in several social networks, each containing partially overlapping sets of personal information. Matching those different profiles allows to create a global profile that gives a holistic view of the information of an individual.
In this seminar I will address this problem and present a first approach which uses the network topology and the publicly available personal information to iteratively match profiles across n social networks.

This is a joint work with Nacéra Bennacer (Supélec), Coriane Nana Jipmo (Supélec) and Antonio Penta (Università di Torino).