Containment of Conjunctive Queries over Databases with Null Values

2006 ◽  
pp. 389-403 ◽  
Author(s):  
Carles Farré ◽  
Werner Nutt ◽  
Ernest Teniente ◽  
Toni Urpí
Keyword(s):  
Conjunctive Queries ◽  
Null Values

Responsibility Analysis for Lineages of Conjunctive Queries with Inequalities

2014 ◽  
Vol 26 (6) ◽  
pp. 1532-1543 ◽  
Author(s):  
Biao Qin ◽  
Shan Wang ◽  
Xiaofang Zhou ◽  
Xiaoyong Du
Keyword(s):  
Conjunctive Queries

scholarly journals Semantic Optimization in Tractable Classes of Conjunctive Queries

2017 ◽  
Vol 46 (2) ◽  
pp. 5-17 ◽  
Author(s):  
Pablo Barceló ◽  
Andreas Pieris ◽  
Miguel Romero
Keyword(s):  
Conjunctive Queries

scholarly journals Efficient Private Conjunctive Query Protocol Over Encrypted Data

Cryptography ◽  
2021 ◽  
Vol 5 (1) ◽  
pp. 2
Author(s):  
Tushar Kanti Saha ◽  
Takeshi Koshiba
Keyword(s):  
Homomorphic Encryption ◽  
Data Access ◽  
Conjunctive Query ◽  
Conjunctive Queries ◽  
Private Data ◽  
Binary Format ◽  
Main Technique ◽  
Batch Technique ◽  
Outsourced Database ◽  
Packing Method

Conjunctive queries play a key role in retrieving data from a database. In a database, a query containing many conditions in its predicate, connected by an “and/&/∧” operator, is called a conjunctive query. Retrieving the outcome of a conjunctive query from thousands of records is a heavy computational task. Private data access to an outsourced database is required to keep the database secure from adversaries; thus, private conjunctive queries (PCQs) are indispensable. Cheon, Kim, and Kim (CKK) proposed a PCQ protocol using search-and-compute circuits in which they used somewhat homomorphic encryption (SwHE) for their protocol security. As their protocol is far from being able to be used practically, we propose a practical batch private conjunctive query (BPCQ) protocol by applying a batch technique for processing conjunctive queries over an outsourced database, in which both database and queries are encoded in binary format. As a main technique in our protocol, we develop a new data-packing method to pack many data into a single polynomial with the batch technique. We further enhance the performances of the binary-encoded BPCQ protocol by replacing the binary encoding with N-ary encoding. Finally, we compare the performance to assess the results obtained by the binary-encoded BPCQ protocol and the N-ary-encoded BPCQ protocol.

Extending the Relational Algebra for Relations with Maybe Tuples and Existential and Universal Null Values

1984 ◽  
Vol 7 (1) ◽  
pp. 129-150
Author(s):  
Joachim Biskup
Keyword(s):  
Relational Algebra ◽  
Null Value ◽  
Null Values ◽  
A Minor

We study operations on generalized database relations which possibly contain maybe tuples and two types of null values. The existential null value has the meaning “value at present unknown” whereas the universal null value has the meaning “value arbitrary”. For extending a usual relational operation to generalized relations we develop three requirements: adequacy, restrictedness, and feasibility. As demonstrated for the natural join as an example, we can essetially meet these requirements although we are faced with a minor tradeoff between restrictedness and feasibility.

scholarly journals Conjunctive queries over trees

2006 ◽  
Vol 53 (2) ◽  
pp. 238-272 ◽  
Author(s):  
Georg Gottlob ◽  
Christoph Koch ◽  
Klaus U. Schulz
Keyword(s):  
Conjunctive Queries

scholarly journals A new interpretation for null values in the weak instance model

1990 ◽  
Vol 41 (1) ◽  
pp. 25-43 ◽  
Author(s):  
Paolo Atzeni ◽  
Maria Cristina De Bernardis
Keyword(s):  
Null Values ◽  
New Interpretation
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