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Chapter 9 Databases Objectives • Understand a DBMS and define its components. • Understand the architecture of a DBMS and its levels. • Distinguish between different database models. • Understand the concept of relational database operations on a relation. • Use Structured Query Language (SQL) to define simple relations. Databases and DBMS • A database is a collection of data that is logically, but not necessarily physically, coherent. • A database management system defines, creates, and maintains a database. • It also allows users controlled access to data in the database. DBMS components Database architecture DB models - hierarchical DB models – network DB model - relational Relation • A relation, in appearance, is a twodementional table. SQL • The structured query language is the standardized language we use to operate on relational databases. • It is a declarative (not procedural) language, which means that the users declare what they want without having to write a step-bystep procedure. Operations on relations - insert insert into COURSES values (“CIS52”, “TCP/IP Protocols”, 6) Operations on relations - delete delete from COURSES where No=“CIS19” Operations on relations - update update COURSES set Unit = 6 where No = “CIS51” Operations on relations - select select * from COURSES where Unit = 5 Operations on relations - project select No, Unit from COURSES Operations on relations - join select No, Course-Name, Unit, Professor from COURSES, TAUGHT-BY where COURSES.No = TAUGHT-BY.No Operations on relations - union select * from CIS15-Roster union select * from CIS52-Roster Operations on relations intersection select * from CIS15-Roster intersection select * from CIS52-Roster Operations on relations difference select * from CIS15-Roster minus select * from CIS52-Roster Objectives • Understand a DBMS and define its components. • Understand the architecture of a DBMS and its levels. • Distinguish between different database models. • Understand the concept of relational database operations on a relation. • Use Structured Query Language (SQL) to define simple relations.