Karina Joyce E. LimboJedan TipuraBLIS-IIIRELATIONAL DATABASE MODEL:LOGICAL VIEW OF DATAANDKEYS
Logical View of Data Logical simplicity yields simpler and more effective database design methodologies.
• The model was first proposed by E.F.Codd in 1970.
EntityAn entity is simply a person, place, event, or thing for which we intend to collect data.Examples:❖ University -- Students, Faculty Members, Courses❖ Airlines -- Pilots, Aircraft, Routes, Supplier
AttributesEach entity has certain characteristics known as attributes.Examples:❖ Student -- Student Number, Name, GPA, Date of Enrollment, Data of Birth, Home Address, Phone Number, Major❖ Aircraft -- Aircraft Number, Data of Last Maintenance, Total Hours Flown, Hours Flown since Last Maintenance
Entities and Attributes A grouping of related entities becomes an entity set.Examples:❖ The STUDENT entity set contains all student entities.❖ The FACULTY entity set contains all faculty entities.❖ The AIRCRAFT entity set contains all aircraft entities
Tables and TheirCharacteristics A table is perceived as a two-dimensional structure composed of rows and columns. Each table row (tuple) represents a single entity within the entity set. Each column represents an attribute and each column has a distinct name. Each row/column intersection represents a single data value
All values in a column must conform to the same data format. Each column has a specific range of values known as the attribute domain. The order of the rows and columns is immaterial to the DBMS Each table must have an attribute or a combination of attributes that uniquely identifies each row.
Table Name: STUDENTE STU_FNAME STU_INIT STU_DOB STU_HRS STU_CLASS STU_GPA STU_TRAN DEPT SFER CODE William C 12-Feb- 42 So 2.84 No BIOL 1975n Anne K 15-Nov- 81 Jr 3.27 Yes CIS 1981 Juliette F 23-Aug- 36 So 2.26 Yes ACCT 1969
Functional Dependence Can be generalized to cover the case in which the determining attribute values occur more than once in a table.
Attribute A determines Attribute B (that is, B is functionally dependent on A) if all of the rows in the table that agree in value for attribute A also agree in value for attribute B.
STUDENT CLASSIFICATIONHOURS COMPLETED CLASSIFICATIONLess than 30 Fr30-59 So60-89 Jr90 or more Sr
STU_HRS STU_CLASS But specific number of hours is not dependent on the classification. In other words, the classification (STU_CLASS) does not determine one and only one value for completed hours (STU_HRS).
Key AttributeAny attribute that is part of a key.Examples:STU_LNAME,STU_FNAME,STU_INIT,STU_PHONE STU_HRS,STU_CLASS
Relational Database KeysSuperkey An attribute (or combination of attributes) that uniquely identifies each entity in a table.
Example:In the STUDENT table..STU_NUMSTU_NUM, STU_LNAMESTU_NUM, STU_LNAME, STU_INIT
Candidate Key A minimal superkey. A superkey that does not contain a subset of attributes that is itself a superkey.
STU_NUM,STU_LNAMEis a superkey, but it is not a candidate key because STU_NUM by itself is a candidate key.
Controlled Redundancy -makes the relational database work. -tables within the database share common attributes that enable the tables to be linked together.