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The concept of the data definition language and its name was first introduced in relation to the [[Codasyl]] database model, where the schema of the [[database]] was written in a [[Syntax (programming languages)|language syntax]] describing the [[Record (computer science)|records]], [[Field (computer science)|fields]], and [[Set (abstract data type)|sets]] of the user [[data model]].<ref>{{cite book|last=Olle|first=T. William|title=The Codasyl Approach to Data Base Management|year=1978|publisher=Wiley|isbn=0-471-99579-7}}</ref> Later it was used to refer to a subset of [[Structured Query Language]] (SQL) for declaring [[Table (database)|tables]], columns, data types and [[Integrity constraints|constraints]]. [[SQL-92]] introduced a schema manipulation language and schema information tables to query schemas<ref name="SQL92">{{cite web |title=Information Technology - Database Language SQL |url=http://www.contrib.andrew.cmu.edu/~shadow/sql/sql1992.txt |website=SQL92 |publisher=Carnegie Mellon |accessdate=12 November 2018}}</ref>. These information tables were specified as [[SQL/Schemata]] in [[SQL:2003]]. The term DDL is also used in a generic sense to refer to any [[formal language]] for describing data or information structures.
==Structured
Many data description languages use a declarative syntax to define columns and data types. Structured query language (e.g., SQL), however, uses a collection of imperative verbs whose effect is to modify the schema of the database by adding, changing, or deleting definitions of tables or other elements. These statements can be freely mixed with other SQL statements, making the DDL not a separate language.
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