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Database relations with null values

Carlo Zaniolo
1984 Journal of computer and system sciences (Print)  
INTRODUCTION The problem of providing a formal treatment for incomplete database information and null values represents one of the thorniest research issues in database theory.  ...  EXTENDED RELATIONS From now on, we will refer to relations with null values simply as relations. To denote relations without nulls we explicitly say "fully defined relations" or "total relations".  ... 
doi:10.1016/0022-0000(84)90080-1 fatcat:nlohgndcwzcwhgcamati6gpshm

Database relations with null values

Carlo Zaniolo
1982 Proceedings of the 1st ACM SIGACT-SIGMOD symposium on Principles of database systems - PODS '82  
INTRODUCTION The problem of providing a formal treatment for incomplete database information and null values represents one of the thorniest research issues in database theory.  ...  EXTENDED RELATIONS From now on, we will refer to relations with null values simply as relations. To denote relations without nulls we explicitly say "fully defined relations" or "total relations".  ... 
doi:10.1145/588115.588117 fatcat:a5nxir4nobg63pef6iwtm2p7cq

Database relations with null values

Carlo Zaniolo
1982 Proceedings of the 1st ACM SIGACT-SIGMOD symposium on Principles of database systems - PODS '82  
INTRODUCTION The problem of providing a formal treatment for incomplete database information and null values represents one of the thorniest research issues in database theory.  ...  EXTENDED RELATIONS From now on, we will refer to relations with null values simply as relations. To denote relations without nulls we explicitly say "fully defined relations" or "total relations".  ... 
doi:10.1145/588111.588117 dblp:conf/pods/Zaniolo82 fatcat:apy25q2tobd5hiwaekd6fgdrcm

Functional Dependencies with Content Null Values in Relational Databases

Cat Ho NGUYN, Thi Thuy Hien BUI
2000 International journal of biomedical soft computing and human sciences  
a sound and complete axiom s.ystem.forlitnctionai dependencies vvith context nulls as wett, Some rutesfor the dota update procedures are also introdttced and examined to ensure that the database ttnder  ...  Kizyword: Retationai Database, Nult Vdtore, Jncomptete bof/ormation, J-tnctionat Dependency.  ...  H; Relational databases with context dependent null values, Journal of computer science and cybernetics, Vol.15, No,1, pp,20-30, 1999. [7] Leyene, M., Loizou G.; The additivity problem for functional dependencies  ... 
doi:10.24466/ijbschs.5.2_85 fatcat:z62g4b54njaubdu52itfwrjbhu

The problem of missing data in geoscience databases

Stephen Henley
2006 Computers & Geosciences  
Relational database theorists advocate that a strict two-valued logic (true/false) be used instead, with prohibition of the use of NULL, and justify this stance by assertion that it is a true representation  ...  One of the most serious problems with SQL is the way it handles missing data. It uses a special value 'NULL' to represent data items whose value is not known.  ...  Acknowledgements The author gratefully acknowledges useful discussions with and helpful suggestions by Professor George Bardossy, Dr. T. Victor Loudon, and Dr. Peter Robson.  ... 
doi:10.1016/j.cageo.2005.12.008 fatcat:3qrs37iqcbb5tcqt5l36gv6twu

Null Value Estimation in Web Environment by using Fuzzy Rule based K-Mean Clustering

Swati Agrawal, Kiran Pandey
2013 International Journal of Computer Applications  
This paper proposed a null value estimation technique based on fuzzy rule based k-means algorithm to deal with that noise.  ...  For evaluating that incomplete information null value estimation is very precious technique.  ...  It can estimate null values in relational database systems more accurately.  ... 
doi:10.5120/12899-9822 fatcat:uhomp2hzhfbhjlqapcdolifcty

Null values in SQL

John Grant
2008 SIGMOD record  
In various writings over the past 20 years, such as [3], Date has pointed out that SQL produces incorrect answers to some queries where a null value is included in a table.  ...  The purpose of this article is to show that, contrary to Rubinson's claim, Date's critique of query evaluation in the presence of null values in SQL is completely justified.  ...  Section 3 provides a historical overview of the evaluation of queries in relational databases involving null values.  ... 
doi:10.1145/1462571.1462575 fatcat:ob3qrr6isfbqnfh45pjgn4k3su

A New Approach for Handling Null Values in Web Server Log

Pradeep Ahirwar, Deepak Singh, Rajesh Wadhvani
2010 International Journal of Advanced Computer Science and Applications  
In this work the issues related to null value are discussed and null value handling concept based on train data set is applied to real MA IT web server log.  ...  The comparisons between different methods for handling null values are depicted.  ...  In recent years many researchers pay heed to the estimating null values in relational database systems.  ... 
doi:10.14569/ijacsa.2010.010101 fatcat:grzsterz5zb3rd5whqyoe4e364

Estimating Null Values in Database Using CBR and Supervised Learning Classification

Khaled Nasser
2014 International Journal of Advanced Computer Science and Applications  
Database and database systems have been used widely in almost, all life activities. Sometimes missed data items are discovered as missed or null values in the database tables.  ...  After training the system to classify and estimate null values under expert supervision, it starts classification and estimation of null data by itself.  ...  RELATED WORK A lot of research effort have been done in estimating null values in DB. The pioneers, Chen, in this area used a new method to estimate null values in relational database in [5] .  ... 
doi:10.14569/ijacsa.2014.050603 fatcat:mf5kuiypyvgwne7dkirrjnhjme

Relational Model and Missing Information

Siniša Jakovljević
2012 JITA - Journal of Information Technology and Applications (Banja Luka) - APEIRON  
The use of predicates in which missing values occur has also been analyzed. Possible effects on system performance have been indicated.  ...  This paper examines possibilities offered by relational model when using missing information. The overview is conducted and possibilities which occur in practial use were analyzed.  ...  Th e issue of comparing null with an existing value is already mentioned.  ... 
doi:10.7251/jit1201032j fatcat:vbxenebb3vfvlgs6iyhhs3qskq

Constraint-based test database generation for SQL queries

Claudio de la Riva, María José Suárez-Cabal, Javier Tuya
2010 Proceedings of the 5th Workshop on Automation of Software Test - AST '10  
The approach is evaluated on a real case study and the results show its feasibility, generating a test database of reduced size with an elevated coverage and mutation score.  ...  Populating test databases with meaningful test data is a difficult task as it involves generating data for many joined tables that must be diverse enough to be able to reveal faults and small enough to  ...  Because the null value could appear in each attribute value, the image of each attribute relation is extended with the NULL data type ({D i +NULL}).  ... 
doi:10.1145/1808266.1808276 dblp:conf/icse/RivaCT10 fatcat:etvh42tvvfehrgs4jhqbaby2oa

Some remarks on self-tuning logical database design

F. De Marchi, M.-S. Hacid, J.-M. Petit
2005 21st International Conference on Data Engineering Workshops (ICDEW'05)  
Moreover, the huge number of null values occurring in practice may incur a significant overhead on his daily work, either to optimize the memory layout or to maintain (or design new) SQL queries.  ...  with respect to SQL workloads and the data themselves.  ...  BCNF wrt their FD -while different with respect to null values or join conditions.  ... 
doi:10.1109/icde.2005.287 dblp:conf/icde/MarchiHP05 fatcat:6aupc5bpbjarlnlqhxirrhhyaa

Functional Dependencies with null Markers

A. Badia, D. Lemire
2014 Computer journal  
To bridge this gap between theory and practice, researchers have proposed definitions of functional dependencies over relations with null markers.  ...  We propose a set of properties that any extension of functional dependencies over relations with null markers should possess. We then propose two new extensions having these properties.  ...  Meanwhile, relational databases use null markers to cope with incomplete information.  ... 
doi:10.1093/comjnl/bxu039 fatcat:kuovz5akvvdm7o4bn5dphczafu

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.  ...  However, if no relation symbol is allowed to appear more than twice, then null-containment is polynomial, as it is for databases without nulls.  ...  All this work did not take into account null values, which are the means by which incomplete information is represented in SQL databases.  ... 
doi:10.1007/11965893_27 fatcat:my72etzbybbnrncwduqko4cooe

Comprehending nulls [article]

James Cheney, Wilmer Ricciotti
2021 arXiv   pre-print
However, SQL's treatment of incomplete information, using nulls and three-valued logic, is not compatible with 'standard' NRC based on two-valued logic.  ...  We give translations relating the implicit and explicit approaches, discuss handling nulls in language integration, and sketch extensions of normalization and conservativity results.  ...  Summing up, we would like to reconcile database queries involving nulls with typed host languages so that: (1) Null values are available at all types and query results including nulls can be translated  ... 
arXiv:2107.11347v1 fatcat:6r6z3mru3nh6fet6lhjwf2k2zi
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