Preference Queries

偏好的概念自然出现在人们谈论人类决策或选择的每一个背景下。 这个项目研究数据库查询上下文中的首选项。 面对信息过载，数据库用户寻求方法来获得不一定是所有的答案查询，而是最好的，最喜欢的answers.In这个项目的框架中，用户的偏好被捕获的偏好公式。 偏好查询涉及使用一些代数偏好运算符，具有简单的形式语义。其中最基本的是winnow，当它应用于一个关系时，返回最优选的元组的集合--那些在关系中不被任何其他元组支配的元组。 winnow运算符由偏好公式参数化。 例如，给定一个合适的公式和一个销售书籍的数据库，winnow将返回购买每本书的所有最便宜的方法。 其他的偏好算子包括排序（无界迭代的winnow）和偏好范围选择。在项目过程中，开发和研究了评估偏好算子的算法。分析了这些算子的代数性质，为优化偏好查询奠定了基础。还开发了用于这种查询的查询优化技术，并将其与现有的查询优化器集成。 该研究解决了所有必要的步骤，使偏好查询在数据库管理领域的一个实用的概念。可在项目网站（http：//www.cse.buffalo.edu/pagchomicki/prefs.html）上获得进一步的资料。更广泛的影响包括学生的新课程，使数据库更好的新应用程序，以及新研究的基础和方向。

The notion of preference occurs naturally in every context where one talks about human decision or choice. This project studies preferences in the context of database queries. Faced with information overload, database users seek ways to obtain not necessarily all answers to queries but rather the best, most preferred answers.In the framework of this project, user preferences are captured as preference formulas. Preference queries involve the use of a number of algebraic preference operators that have simple formal semantics. The most basic of those is winnow which, when applied to a relation, returns the set of the most preferred tuples -- those which are not dominated by any other tuples in the relation. The winnow operator is parameterized by a preference formula. For example, given a suitable formula and a database of books for sale winnow will return all the cheapest ways to purchase every book. Other preference operators include ranking (unbounded iteration of winnow) and preference range selection.In the course of the project algorithms for evaluating preference operators are developed and studied. Algebraic properties of those operators are identified, in order to lay the foundation for the optimization of preference queries. Query optimization techniques for such queries are also developed and integrated with an existing query optimizer. The research addresses all the steps necessary to make preference queries a practical concept in the area of database management. Further information can be obtained at the project web site (http://www.cse.buffalo.edu/~chomicki/prefs.html). Broader impacts include new courses for students, new applications to make databases better, and foundation and directions for new research.