Union Operation Notation:rs Defined as: rUs={tlt∈rort∈S} For rs to be valid. 1.r,s must have the same arity (same number of attributes) 2.The attribute domains must be compatible(example:2nd column of rdeals with the same type of values as does the 2nd column of s) Example:to find all courses taught in the Fall 2009 semester,or in the Spring 2010 semester,or in both ncourse_id(semester="Fall"Ayear=2009(section)) Ilcourse_id(o semester="Spring"A year=2010(section)) Database System Concepts-6th Edition 6.6 ©Silberschat乜，Korth and SudarshanDatabase System Concepts - 6 6.6 ©Silberschatz, Korth and Sudarshan th Edition Union Operation Notation: r  s Defined as: r  s = {t | t  r or t  s} For r  s to be valid. 1. r, s must have the same arity (same number of attributes) 2. The attribute domains must be compatible (example: 2nd column of r deals with the same type of values as does the 2nd column of s) Example: to find all courses taught in the Fall 2009 semester, or in the Spring 2010 semester, or in both course_id ( semester=“Fall” Λ year=2009 (section))  course_id ( semester=“Spring” Λ year=2010 (section))