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A NOT NULL constraint is functionally equivalent to the following check constraint with an IS NOT NULL predicate: . CHECK (column IS NOT NULL) Some relational database management systems are able to optimize performance when the NOT NULL constraint syntax is used as opposed to the CHECK constraint syntax given above.
Model-theoretic grammars, also known as constraint-based grammars, contrast with generative grammars in the way they define sets of sentences: they state constraints on syntactic structure rather than providing operations for generating syntactic objects. [1]
Constraint grammar (CG) is a methodological paradigm for natural language processing (NLP). Linguist-written, context -dependent rules are compiled into a grammar that assigns grammatical tags ("readings") to words or other tokens in running text.
SQL implements constraint functionality in the form of check constraints. Constraints restrict the data that can be stored in relations. These are usually defined using expressions that result in a Boolean value, indicating whether or not the data satisfies the constraint. Constraints can apply to single attributes, to a tuple (restricting ...
A check constraint placed on a column operates under a slightly different set of rules than those for the DML WHERE clause. While a DML WHERE clause must evaluate to True for a row, a check constraint must not evaluate to False. (From a logic perspective, the designated values are True and Unknown.) This means that a check constraint will ...
A constraint programming language is a declarative programming language where relationships between variables are expressed as constraints. Execution proceeds by attempting to find values for the variables which satisfy all declared constraints. Claire; Constraint Handling Rules; CHIP; ECLiPSe; Kaleidoscope; Raku [8]
The "block structure" aspect that context-free grammars capture is so fundamental to grammar that the terms syntax and grammar are often identified with context-free grammar rules, especially in computer science. Formal constraints not captured by the grammar are then considered to be part of the "semantics" of the language.
This check is essential for programs that use file handling. Format check Checks that the data is in a specified format (template), e.g., dates have to be in the format YYYY-MM-DD. Regular expressions may be used for this kind of validation. Presence check Checks that data is present, e.g., customers may be required to have an email address ...