TAILIEUCHUNG - Lecture Fundamentals of database systems: Chapter 6 - Emasri, Navathe

In this chapter we discuss the two formal languages for the relational model: the relational algebra and the relational calculus. The main contents in this chapter include: Example database application (COMPANY), overview of the QBE language (appendix D),. Inviting you to refer. | SET DIFFERENCE also called MINUS or EXCEPT is denoted by - The result of R - S is a relation that includes all tuples that are in R but not in S The attribute names in the result will be the same as the attribute names in R The two operand relations R and S must be type compatible Copyright 2007 Ramez Elmasri and Shamkant B. Navathe lide 6- 3 Notice that both union and intersection are commutative operations that is R o S S o R and R n S S n R Both union and intersection can be treated as n-ary operations applicable to any number of relations as both are associative operations that is R o S o T R o S o T R n S n T R n S n T The minus operation is not commutative that is in general R-S S-R Copyright 2007 Ramez Elmasri and Shamkant B. Navathe Slide 6-4 CARTESIAN or CROSS PRODUCT Operation This operation is used to combine tuples from two relations in a combinatorial fashion. Denoted by R A1 A2 . . . An x S B1 B2 . . . Bm Result is a relation Q with degree n m attributes Q A1 A2____An B1 B2___Bm in that order. The resulting relation state has one tuple for each combination of tuples one from R and one from S. Hence if R has nR tuples denoted as R nR and S has nS tuples then R x S will have nR nS tuples. The two operands do NOT have to be type compatible Generally CROSS PRODUCT is not a meaningful operation Can become meaningful when followed by other operations Example not meaningful FEMALE_EMPS a seX .f. EMPLOYEE EMPNAMES . fnamel name ssn FEMALE_EMPS EMP_DEPENDENTS EMPNAMES x DEPENDENT EMP_DEPENDENTS will contain every combination of EMPNAMES and DEPENDENT whether or not they are actually related Copyright 2007 Ramez Elmasri and Shamkant B. Navathe lide 6 Copyright 2007 Ramez Elmasri and Shamkant B. Navathe lide 6- 6 1 To keep only combinations where the DEPENDENT is related to the EMPLOYEE we add a SELECT operation as follows Example meaningful FEMALE_EMPS a SEX F EMPLOYEE EMPNAMES fnamelName ssn FEMALE_EMPS EMP_DEPENDENTS EMPNAMES x DEPENDENT ACTUAL_DEPS a ssn .

• Cơ sở dữ liệu
• Fundamentals of Database Systems
• Database Systems
• Relational algebra
• Relational calculus
• Database application
• Relational model
• Database system concepts
• The relational data model
• Database design
• Database programming techniques
• Relational database constraints
• Database architecture
• Data models
• Hierarchical model
• Relational database design algorithms
• Designing a set of relations
• Relational decompositions
• Relational database schema
• Database users
• Database applications
• Typical DBMS functionality
• Database approach
• Databases and database users
• Relational databases
• Physical database design
• Concurrency control techniques
• Database recovery techniques
• Database security
• Distributed databases
• Database management systems
• Fundamentals of database management systems
• Logical database design
• Object oriented database management
• Data administration
• Relational model concepts
• Relational model constraints
• Characteristics of relations
• Relational database design
• EERR to Relational mapping
• Mapping EER model constructs
• ER to Relational mapping algorithm
• Database design process
• ER model concepts
• ER diagrams
• Relational database schemas
• Multivalued dependencies
• Database design theory
• File structures
• Query processing
• Database tuning
• Transaction processing
• Concurrency control
• Database System
• Lecture Database Systems
• Enhanced Entity Relationship
• UML modeling
• Enhanced ER model
• Fundamentals of data modeling
• Data modeling
• Entity Relationship
• Programming techniques
• Database programming
• SQL Triggers
• Views in SQL
• Data independence
• Database system utilities
• Classification of DBMSs
• Embedded SQL
• Functions calls
• Stored procedures
• Relational data retrieval
• Relational database model