We answer the question which conjunctive queries are uniquely characterized by polynomially many positive and negative examples, and how to construct such examples efficiently. As a consequence, we obtain a new efficient exact learning algorithm for a class of conjunctive queries. At the core of our contributions lie two new polynomial-time algorithms for constructing frontiers in the homomorphism lattice of finite structures. We also discuss implications for the unique characterizability and learnability of schema mappings and of description logic concepts.

翻译：我们回答这样一个问题,即哪些结合性查询具有独特的特征,其特征是多方面的正面和负面例子,以及如何有效地构建这些例子。 因此,我们获得了一种新的高效的精确学习算法,用于一组结合性查询。 我们贡献的核心是两种新的多元时间算法,用于在有限结构的同质结构的边板上构建边界。 我们还讨论了系统绘图和描述逻辑概念的独特特征和可学习性的影响。