Chapter 13 3 Databases Invitation to Computer Science

Chapter 13. 3: Databases Invitation to Computer Science, Java Version, Second Edition

Databases n An electronic database q Stores data items q Data items can be extracted q Data items can be sorted q Data items can be manipulated to reveal new information Invitation to Computer Science, Java Version, Second Edition 2

Data Organization n Byte q q q n A group of eight bits Can store the binary representation of a single character or of a small integer number A single unit of addressable memory Field q A group of bytes used to represent a string of characters Invitation to Computer Science, Java Version, Second Edition 3

Data Organization (continued) n Record q n Data file q n A collection of related fields Related records are kept in a data file Database q Related files make up a database Invitation to Computer Science, Java Version, Second Edition 4

Figure 13. 3 Data Organization Hierarchy Invitation to Computer Science, Java Version, Second Edition 5

Figure 13. 4 Records and Fields in a Single File Invitation to Computer Science, Java Version, Second Edition 6

Figure 13. 5 One Record in the Rugs-For-You Employees File Invitation to Computer Science, Java Version, Second Edition 7

Database Management Systems n Database management system (DBMS) q n Manages the files in a database Relational database model q Conceptual model of a file as a two-dimensional table Invitation to Computer Science, Java Version, Second Edition 8

Database Management Systems (continued) n In a relational database q q A table represents information about an entity A row contains data about one instance of an entity q A row is called a tuple q Each category of information is called an attribute Invitation to Computer Science, Java Version, Second Edition 9

Figure 13. 6 Employees Table for Rugs-For-You Invitation to Computer Science, Java Version, Second Edition 10

Figure 13. 7 Insurance. Policies Table for Rugs-For-You Invitation to Computer Science, Java Version, Second Edition 11

Database Management Systems (continued) n Specialized query languages q q n Enable the user or another application program to query the database Example: SQL (Structured Query Language) Relationships among different entities in a database q Established through the correspondence between primary keys and foreign keys Invitation to Computer Science, Java Version, Second Edition 12

SELECT ID, LASTNAME, FIRSTNAME, PAYRATE FROM EMPLOYEES WHERE LASTNAME = ‘KAY’ ; Invitation to Computer Science, Java Version, Second Edition 13

Figure 13. 8 Three Entities in the Rugs-For-You Database Invitation to Computer Science, Java Version, Second Edition 14

Other Considerations n Performance issues q q q Large files are maintained on disk Organizing record storage on disk can minimize time to access a particular record Creating additional records to be stored with the file can significantly reduce access time Invitation to Computer Science, Java Version, Second Edition 15

Other Considerations (continued) n Distributed databases q n Allow physical data to reside at separate and independent locations that are networked Massive, integrated government databases raise legal, political, social, and ethical issues Invitation to Computer Science, Java Version, Second Edition 16

Summary n Database: allows data items to be stored, extracted, sorted, and manipulated n Relational database model: conceptual model of a file as a two-dimensional table Invitation to Computer Science, Java Version, Second Edition 17