Towards Approximating Incomplete Queries over Partially Complete Databases (Extended Abstract)

Expanding Queries to Incomplete Databases by Interpolating General Logic Programs

In databases, queries are usually deened on complete databases. In this paper we introduce and motivate the notion of extended queries that are deened on incomplete databases. We argue that the language of extended logic program is appropriate for representing extended queries. We show through examples that given a query, a particular extension of it has important characteristics which correspo...

Efficient Algorithms for Approximating Answers to Queries Against Incomplete Relational Databases

Computing Possible and Certain Answers over Order-Incomplete Data

This paper studies the complexity of query evaluation for databases whose relations are partially ordered; the problem commonly arises when combining ordered data from multiple sources. We focus on queries in a useful fragment of SQL, namely positive relational algebra with aggregates, whose bag semantics we extend to the partially ordered setting. Our semantics leads to the study of two main c...

Ontology-Mediated Queries for Probabilistic Databases (Extended Abstract)

The semantics of large-scale knowledge bases like NELL and Google’s Knowledge Vault is founded on (tuple-independent) probabilistic databases (PDBs) [3]. As for ordinary databases, they employ the closed-world assumption, i.e., missing facts are treated as being false (having the probability 0), which leads to unintuitive results when querying PDBs. Recently, open-world probabilistic databases ...

Efficient Evaluation of Well-designed Pattern Trees (Extended Abstract)

Conjunctive queries (CQs) constitute the core of the query languages for relational databases and also the most intensively studied querying mechanism in the database theory community. But CQs suffer from a serious drawback when dealing with incomplete information: If it is not possible to match the complete query with the data, they return no answer at all. The semantic web therefore provides ...