Functional dependencies in relations with null values
Information Processing Letters
Set-theoretic problems of null completion in relational databases
Information Processing Letters
On semantic issues connected with keys in relational databases permitting null values
Journal of Information Processing and Cybernetics
Null values in nested relational databases
Acta Informatica
A database needs two kinds of negation
MFDBS 91 Proceedings of the 3rd symposium on Mathematical fundamentals of database and knowledge base systems
ACM SIGMOD Record
A unified treatment of null values using constraints
Information Sciences: an International Journal
On semantic issues connected with incomplete information databases
ACM Transactions on Database Systems (TODS)
Entity-Relationship Modeling: Foundations of Database Technology
Entity-Relationship Modeling: Foundations of Database Technology
Null values in data base management a denotational semantics approach
SIGMOD '79 Proceedings of the 1979 ACM SIGMOD international conference on Management of data
The additivity Problem for Data Dependencies in Incomplete Relational Databases
Selected Papers from a Workshop on Semantics in Databases
Multivalued dependencies with null values in relational data bases
VLDB '79 Proceedings of the fifth international conference on Very Large Data Bases - Volume 5
ACM SIGMOD Record
Logic and Databases: The Roots of Relational Theory
Logic and Databases: The Roots of Relational Theory
When data dependencies over SQL tables meet the logics of paradox and S-3
Proceedings of the twenty-ninth ACM SIGMOD-SIGACT-SIGART symposium on Principles of database systems
Database Explorations: Essays on The Third Manifesto and related topics
Database Explorations: Essays on The Third Manifesto and related topics
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NULL is a special marker used in SQL to indicate that a value for an attribute of an object does not exist in the database. Its aim is a representation of “missing information and inapplicable information”. Although NULL is called null 'value' is not at all a value. It is a marker. It is only an annotation of incomplete data. Since it is typically interpreted as a value, NULL has led to controversies and and debates because of its treatment by 3-valued logics, of its special requirements for its use in SQL joins, and the special handling required by aggregate functions and SQL grouping operators. The three-valued logics does not properly reflect the nature of this special marker. Markers should be based on their specific data type. This data type is then different from any other data types used in relational database technology. Due to this orthogonality we can combine any type with the special type. To support this we introduce a non-standard generalisation of para-consistent logics. This logics reflects the nature of these markers. This paper aims in developing a general approach to NULL 'values' and shows how they can be used without changing database technology.