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In database systems, atomicity (/ ˌ æ t ə ˈ m ɪ s ə t i /; from Ancient Greek: ἄτομος, romanized: átomos, lit. 'undividable') is one of the ACID (Atomicity, Consistency, Isolation, Durability) transaction properties. An atomic transaction is an indivisible and irreducible series of database operations such that either all occur ...
Hugh Darwen and Chris Date have suggested that Codd's concept of an "atomic value" is ambiguous, and that this ambiguity has led to widespread confusion about how 1NF should be understood. [7] [8] In particular, the notion of a "value that cannot be decomposed" is problematic, as it would seem to imply that few, if any, data types are atomic:
A relational database schema is defined as a tuple S = (D, R, h) where D is the domain of atomic values (see relational model for more on the notions of domain and atomic value), R is a finite set of relation names, and h : R → 2 C. a function that associates a header with each relation name in R. (Note that this is a simplification from the ...
Another basic notion is the set of atomic values that contains values such as numbers and strings. Our first definition concerns the notion of tuple, which formalizes the notion of row or record in a table: Tuple A tuple is a partial function from attribute names to atomic values. Header A header is a finite set of attribute names. Projection
The database schema is the structure of a database described in a formal language supported typically by a relational database management system (RDBMS). The term "schema" refers to the organization of data as a blueprint of how the database is constructed (divided into database tables in the case of relational databases).
A database relation (e.g. a database table) is said to meet third normal form standards if all the attributes (e.g. database columns) are functionally dependent on solely a key, except the case of functional dependency whose right hand side is a prime attribute (an attribute which is strictly included into some key).
[5] [6] A relational database definition (database schema, sometimes referred to as a relational schema) can thus be thought of as a collection of named relation schemas. [7] [8] In implementations, the domain of each attribute is effectively a data type [9] and a named relation schema is effectively a relation variable (relvar for short).
Atomicity is the guarantee that series of database operations in an atomic transaction will either all occur (a successful operation), or none will occur (an unsuccessful operation). The series of operations cannot be separated with only some of them being executed, which makes the series of operations "indivisible".