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Containment of Conjunctive Queries over Databases with Null Values [chapter]

Carles Farré, Werner Nutt, Ernest Teniente, Toni Urpí
2006 Lecture Notes in Computer Science  
We study containment of conjunctive queries that are evaluated over databases that may contain tuples with null values.  ...  This problem ("null containment" for short) is different from containment over databases without null values and sometimes more difficult.  ...  In the present paper we study null containment of conjunctive queries, that is, containment under set semantics over databases that contain null values, where conditions involving nulls are evaluated as  ... 
doi:10.1007/11965893_27 fatcat:my72etzbybbnrncwduqko4cooe

Query-driven Data Completeness Management (PhD Thesis) [article]

Simon Razniewski
2015 arXiv   pre-print
We then present techniques for drawing inferences between such statements and statements about the completeness of query answers, and show how the techniques can be extended to databases that contain null  ...  values.  ...  Query Completeness The result of query evaluation over databases with null values may vary depending on whether the nulls are interpreted as Codd or as SQL nulls.  ... 
arXiv:1411.2855v3 fatcat:z77sm2w3ajbbhkorlzvnooebfy

Open and Closed World Assumptions in Data Exchange

Leonid Libkin, Cristina Sirangelo
2009 International Workshop on Description Logics  
Such a database is formally a relational structure over the disjoint union of two domains: D of data values, and V of variables (or nulls, usually denoted by the symbol ⊥ with subscripts).  ...  Hence, the problem of answering queries in data exchange is reduced to the well-studied problems of answering queries in closedworld databases with nulls.  ... 
dblp:conf/dlog/Libkin09 fatcat:su5nurerxbei3pgumd54picecy

The Incomplete Database

Karen L. Kwast
1991 International Joint Conference on Artificial Intelligence  
The introduction of nulls (unknown values) in the relational database calls for an extension of the theoretical foundation of the database model.  ...  A sound model-theoretical foundation of nulls in a relational database based on modal logic is presented here. The modal interpretation of queries is easy to comprehend and intuitively correct.  ...  This paper deals with the theoretical foundation of nulls in a relational database. Unknown values Let nulls represent the unknown values in a relational database.  ... 
dblp:conf/ijcai/Kwast91 fatcat:wwgf6tedkvhmdjsjpx4uxbkr3m

Achieving Data Privacy through Secrecy Views and Null-Based Virtual Updates [article]

Leopoldo Bertossi, Lechen Li
2012 arXiv   pre-print
For a user without permission to access that sensitive data, the database instance he queries is updated to make the contents of the views empty or contain only tuples with null values.  ...  Virtual updates are based on the use of null values as used in the SQL standard. We provide the semantics of secrecy views and the virtual updates.  ...  Semantics of query answers with nulls Here we introduce the semantics of FO conjunctive query answering in relational databases with null values. 5 More precisely, in SQL relational databases with a  ... 
arXiv:1105.1364v3 fatcat:pzzwd2k2frfsbdy3edgvoznbv4

Achieving Data Privacy through Secrecy Views and Null-Based Virtual Updates

Leopoldo Bertossi, Lechen Li
2013 IEEE Transactions on Knowledge and Data Engineering  
The database, before returning the answers to a query posed by a restricted user, is updated to make the secrecy views empty or a single tuple with null values.  ...  Index Terms-Data privacy, views, query answering, null values, view updates, answer set programs, database repairs.  ...  Support from Georg Gottlob, Thomas Eiter and a Pauli Fellowship of the "Wolfgang Pauli Institute, Vienna" is highly appreciated.  ... 
doi:10.1109/tkde.2012.86 fatcat:fzxrqwny2bdrvjmipodq6o2fr4

Incompleteness in information integration

Evgeny Kharlamov, Werner Nutt
2008 Proceedings of the VLDB Endowment  
More specifically, we aim to extend current query answering techniques for local-, and global-as-view integration to integration of tables with SQL nulls, Codd tables, etc.  ...  In our work we aim to extend current results on virtual integration by considering various forms of incompleteness at the level of the sources, the integrated database and the queries (we call this Incomplete  ...  In [11] the problem of containment of conjunctive queries over DBs with ω was studied.  ... 
doi:10.14778/1454159.1454242 fatcat:rgx2mzysdjfczpz5nskpb7mvmq

The Impact of Disjunction on Reasoning under Existential Rules: Research Summary [article]

Michael Morak
2014 arXiv   pre-print
Query answering over databases with respect to a Datalog+/- theory is generally undecidable, however several syntactic restrictions have been proposed to remedy this fact.  ...  It is the precise objective of the doctoral thesis herein discussed, to investigate the impact on the complexity of query answering, of adding disjunction to well-known decidable Datalog+/- fragments,  ...  where a null value can occur during the chase with respect to a set of TGDs Σ.  ... 
arXiv:1405.5109v1 fatcat:4al4oxnkenb7pe3q64zqgtfet4

Using Integrity Constraints to Provide Intensional Answers to Relational Queries

Amihai Motro
1989 Very Large Data Bases Conference  
An intensionalanswer to a query is a set of characterizations of the set of database values that satisfy the query (the extensional answer).  ...  These intensional answers characterize the extensional answers in two ways: (1) with constraints that are applicable to the extensional answer, and (2) with database views that are contained entirely in  ...  In the relational database model extensional information is expressed with relations over domains of data values, and intensional information is expressed with constraints, which are formulas in predicate  ... 
dblp:conf/vldb/Motro89 fatcat:w3dirt25kfah3fcntybsebrz6q

Databases under the Partial Closed-world Assumption: A Survey

Simon Razniewski, Werner Nutt
2014 Workshop Grundlagen von Datenbanken  
In this survey we review foundational and work on the partial closed-world assumption and then discuss work done in our group in recent years on various aspects of reasoning over databases under this assumption  ...  Traditionally, it is assumed that a database reflects exactly the state of affairs in an application domain, that is, a fact that is true in the real world is stored in the database, and a fact that is  ...  This work has been partially supported by the project "MAGIC: Managing Completeness of Data" funded by the province of Bozen-Bolzano.  ... 
dblp:conf/gvd/RazniewskiN14 fatcat:5fn45yrqfnbkjos4ghzbxt725q

Queries with Arithmetic on Incomplete Databases

Marco Console, Matthias Hofer, Leonid Libkin
2020 Proceedings of the 39th ACM SIGMOD-SIGACT-SIGAI Symposium on Principles of Database Systems  
Part of this work was done while the third author was at IRIF, Université de Paris, and DI-ENS, supported by a grant from the Foundation Sciences Mathématiques de Paris.  ...  Each column, whether of base type or numerical, may contain null values.  ...  Thus, an incomplete database represents complete (i.e., having no nulls) databases ( ), where ranges over valuations, and ( ) is the result of replacing each null ⊥ ∈ N( ) with (⊥).  ... 
doi:10.1145/3375395.3387666 dblp:conf/pods/ConsoleHL20 fatcat:lpkmbod7vjaglhtxvgwpbmmbju

Data Exchange: Query Answering for Incomplete Data Sources

Foto Afrati, Chen Li, Vassia Pavlaki
2008 Proceedings of the Third International ICST Conference on Scalable Information Systems  
We use the chase to compute a universal instance which is materialized over the target schema and is used to compute the certain answers to unions of conjunctive queries.  ...  We prove that computing certain answers (under both semantics) for unions of conjunctive queries can be done in polynomial time when the schema mapping contains constraints that consist of a weakly acyclic  ...  A conjunctive query q(x) over a schema T is a formula of the form ∃yϕ(x, y), where ϕ(x, y) is a conjunction of atomic formulas over T.  ... 
doi:10.4108/icst.infoscale2008.3476 dblp:conf/infoscale/AfratiLP08 fatcat:qjsyv3ueofde7dneihyqotjc64

When is naive evaluation possible?

Amélie Gheerbrant, Leonid Libkin, Cristina Sirangelo
2013 Proceedings of the 32nd symposium on Principles of database systems - PODS '13  
The term naïve evaluation refers to evaluating queries over incomplete databases as if nulls were usual data values, i.e., to using the standard database query evaluation engine.  ...  For relational databases it is well known that unions of conjunctive queries possess this desirable property, and results on preservation of formulae under homomorphisms tell us that within relational  ...  of conjunctive queries.  ... 
doi:10.1145/2463664.2463674 dblp:conf/pods/GheerbrantLS13 fatcat:2xzu3dj4xzbpvjvoefjtxvxqd4

Data exchange and incomplete information

Leonid Libkin
2006 Proceedings of the twenty-fifth ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems - PODS '06  
over target instances in a way that is semantically consistent with the information in the source.  ...  with nulls have not been used, and the distinction between closed and open world semantics has not been made.  ...  Acknowledgments Discussions with Marcelo Arenas during the early stages of this project were very helpful. I thank Pablo Barceló, Ronald Fagin, and anonymous reviewers for their comments.  ... 
doi:10.1145/1142351.1142360 dblp:conf/pods/Libkin06 fatcat:dd2hfahxtrcz7kvcml3w5wlqza

A Note on Computing Certain Answers to Queries over Incomplete Databases

Marcelo Arenas, Elena Botoeva, Egor V. Kostylev, Vladislav Ryzhikov
2017 Alberto Mendelzon Workshop on Foundations of Data Management  
An incomplete database I with such nulls then represents a set of databases with complete information, called representations of I, each of which is obtained by replacing nulls by actual values.  ...  Computing Certain Answers In this section, we focus on the problem of computing cert(Q, I) for a union of conjunctive queries Q with inequalities (UCQ = ) and an incomplete database I.  ... 
dblp:conf/amw/ArenasBKR17 fatcat:jup3iz7xxjd6jgseuwcp2pq6me
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