Database System - 3rd theory class : Formal Relational Query Languages 20/03/16
Formal Relational Query Languages (形式化查询语言)
Query Language : language in which users request information from the database
Categories of languages :
Relational Algebra (关系代数) non-procedural (非过程性)
Turple Kelational (元组关系演算) / Domain Relational Calculus (域关系演算)
" Pure language "
Relational Algebra → Procedural language
operations : Union (并) / Intersection (交) / Defference (差) / Cartesian Product (笛卡尔积) / Project (投影) / Select (选择) / Join (连接) / Division (除)
Campatibility (相容性)
