Research Interests:

My research is mainly in two areas of information systems:

• Semi-structured databases (e.g., XML and Web databases) often contain incomplete data. The user's knowledge of the structure of such databases is often partial or incorrect. My research focuses on defining query languages that compensate for these problems by returning answers with different degrees of flexibility (e.g., EquiX, XSQL, XSearch) and on fundamental problems that arise in this context.
• A trend toward data warehousing, i.e., storing huge amounts of detailed historical data has recently emerged. The sheer mass of the data being stored leads to immense difficulties when attempting to efficiently access the information. Since data warehouses are usually accessed by aggregate queries, an understanding of aggregate query optimization is needed. My contributions include characterizing equivalence for varied aggregate queries and defining query rewriting techniques.

Here are some topics that I am working on (or interested in working on):

• Automatic generation of data by user requirements
• Fundamental problems in inexact querying
• Querying virtual databases (e.g., personal computers, personal Web "history" list)
• Optimization of queries which combine bag and bag-set semantics
• Aggregate queries with HAVING clause
• Ranking for Desktop Search

Teaching:

This semester I am teaching Databases, and co-teaching a Seminar on Databases in the Internet, together with Prof. Yehoshua Sagiv. Next semester I will be giving a new course on advanced topics in databases.

Program Committee Member:

DBPL 2005, EDBT 2006, ICDE 2007, PODS 2007, VLDB 2007, VLDB 2008, ICDT 2009, VLDB 2009, DEXA 2009, ICDE 2010, ICDT 2010, ICDT 2011, PODS 2011, ICDT 2013

Tutorials:

Enumerating Large Query Results (ICDE 2009)

Publications:

Here are some of my publications. (I wish that a bunny jumping on my keyboard could write them. It would make life much simpler . The full version, when available, is a zip file containing a postscript file. If the file is not available online, you can contact me and I will usually be able to send you a copy. Note to myself: This list is very outdated. Must update soon.

Journal Papers

• Rewriting Queries with Arbitrary Aggregation Functions Using Views.
  S. Cohen, W. Nutt, Y. Sagiv.
  The ACM Transactions on Database Systems (TODS) 31(2) 2006.
• Equivalences among Aggregate Queries with Negation. (download here)
  S. Cohen, W. Nutt, Y. Sagiv.
  The ACM Transactions on Computational Logic (TOCL) 6(2) 2005.
• EquiX - A Search and Query Language for XML. (abstract, paper)
  S. Cohen, Y. Kanza, Y. Kogan, W. Nutt, Y. Sagiv, A. Serebrenik.
  Journal of the American Society for Information Science and Technology (JASIST), 2001.

Invited Papers:

• Survey on Containment of Aggregate Queries
  S. Cohen
  Sigmod Record. March 2005.

Conference Papers:

• Full Disjunctions: Polynomial-Delay Iterators in Action
  Sara Cohen, Itzhak Fadida, Yaron Kanza, Benny Kimelfeld, Yehoshua Safiv.
  Proceedings of the 32nd Internation Conference on Very Large Data Bases (VLDB)., 2006.
• Count-Constraints for Generating XML
  Sara Cohen.
  Proceedings of the 6th Workshop on Next Generation Information Systems (NGITS), 2006.
• User-Defined Aggregate Functions: Bridging Theory and Practice. (abstract, paper)
  Sara Cohen.
  Proceedings of the ACM SIGMOD International Conference on Management of Data, 2006.
• Equivalence of Queries Combining Set and Bag-Set Semantics. (abstract, paper)
  S. Cohen.
  Proceedings of the 25th ACM Symposium on Principles of Database Systems (PODS), 2006.
• Interconnection semantics for keyword search in XML. (abstract, paper)
  S. Cohen, Y. Kanza, B. Kimelfeld, Y. Sagiv.
  Proceedings of the 2005 ACM CIKM International Conference on Information and Knowledge Management, 2005.
• An Incremental Algorithm for Computing Ranked Full Disjunctions. (abstract, paper)
  S. Cohen and Y. Sagiv.
  Proceedings of the 24th ACM Symposium on Principles of Database Systems (PODS), 2005.
• An Abstract Framework for Generating Maximal Answers to Queries. (abstract, paper)
  S. Cohen and Y. Sagiv.
  The 10th International Conference on Database Theory (ICDT). January 2005.
• XSEarch: A Semantic Search Engine for XML. (abstract, paper)
  S. Cohen, J. Mamou, Y. Kanza, Y. Sagiv.
  The 29th International Conference on Very Large Databases (VLDB). September 2003.
• Generating Relations from XML Documents. (abstract, paper)
  S. Cohen, Y. Kanza, Y. Sagiv.
  The 9th International Conference on Database Theory (ICDT). January 2003.
• Containment of Aggregate Queries. (abstract, paper, extended version)
  S. Cohen, W. Nutt, Y. Sagiv.
  The 9th International Conference on Database Theory (ICDT). January 2003.
• Select Project Queries for XML Documents. (abstract, paper)
  S. Cohen, Y. Kanza, Y. Sagiv.
  Proceedings of the 5th Workshop on Next Generation Information Systems (NGITS). 2002.
• SQL4X: A Flexible Query Language for XML and Relational Databases. (abstract, paper)
  S. Cohen, Y. Kanza, Y. Sagiv.
  8th Biennial Workshop on Data Bases and Programming Languages (DBPL), 2001.
• Equivalences Among Aggregate Queries with Negation. (abstract, paper)
  S. Cohen, W. Nutt, Y. Sagiv.
  Proceedings of the 20th ACM Symposium on Principles of Database Systems (PODS), 2001.
• Combining the Power of Searching and Querying. (abstract, paper)
  S. Cohen, Y. Kanza, Y. Kogan, W. Nutt, Y. Sagiv, A. Serebrenik.
  Proceedings of the 5th IFCIS International Conference on Cooperative Information Systems (CoopIS), 2000.
• Algorithms for Rewriting Aggregate Queries Using Views. (abstract, paper)
  S. Cohen, W. Nutt, A. Serebrenik.
  Proceedings of the 4th Symposium on Advances in Database and Information Systems (ADBIS,-DASFAA), 2000.
• EquiX - Easy Querying in XML Databases. (abstract, paper)
  S. Cohen, Y. Kanza, Y. Kogan, W. Nutt, Y. Sagiv, A. Serebrenik.
  ACM Workshop on The Web and Databases (WebDB), 1999.
• Rewriting Aggregate Queries Using Views. (abstract, paper)
  S. Cohen, W. Nutt, A. Serebrenik.
  Proceedings of the 18th> ACM Symposium on Principles of Database Systems (PODS), 1999.
• Deciding Equivalences among Aggregate Queries. (abstract, paper)
  W. Nutt, Y. Sagiv, S. Shurin (Cohen). Proceedings of the 17th ACM Symposium on Principles of Database Systems (PODS), 1998. Long version

PhD. Thesis

• Equivalence, Containment and Rewriting of Aggregate Queries. (paper) Sara Cohen. PhD Thesis, 2004.

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Old (Prehistoric) Projects:

• SQL4X - A system for integrating XML and relations. It was implemented over an Oracle database.
• PrologDoc A tool for generating html documentation out of Prolog programs. This system was developed with Elisheva Bonchek using SICStus Prolog. It was subsequently used for commercial purposes. It is now being maintained here.

Personal:

I am married to Chaim, and have six beautiful children.