Databases Database Information is not useful if not
Databases Database Information is not useful if not organized In database, data are organized in a way that people find meaningful and useful. Database Management System (DBMS) is used to input, sort, organize and store data.
Figure 14-1 DBMS Components Hardware: the physical computer system Software: the program that allows users to access, maintain update the data Data: Data are stored on the computer. In database data are separate entity from the software that access them
Users: could be either (1) end users: people who has access to the database or (2) application program: applications that access and process data Procedures: rules that are defined and followed by the users Database architecture Internal Level: Interact directly with the hardware Conceptual Level: (1) Define
the logical view of the data. (2) Define the data model. (3) Contain the main functions of the DBMS (4) Intermediary level that free users from dealing with internal level External Level: (1) Interact directly with users (2)
Display data in familiar format Database Model Database model defines the logical design of data. Database model describes the relation between different parts of data. There are three database models:
1. Hierarchical Model 2. Network Model 3. Relational Model Hierarchical model Data are organized in an upside down tree Each entity has one parent and many children Old and not used now
Network model Entities are organized in a graph Entities can be accessed through several paths Old and not used Relational model
Data are organized in two dimensional tables (relations) Tables re related to each other Relational Database Management System (RDBMS) are more common model used today Relation (Name, Attributes, Tuples) Attributes are the column
heading Each column must have a unique heading Number of columns is called the degree of the relation
Tuple is a collection of attribute value Total number of rows
is called Cardinality of the relation Each relation must have a unique name Name Relation appears in 2 dimensional table
That doesnt mean data stored as table; the physical storage of data is independent of the logical organization of data OPERATIONS ON RELATIONS Insert operation
Unary operation Insert Operation: Inserts new tuple into the relation Delete operation Unary operation Delete Operation: Deletes tuple from the relation
Update operation Unary operation Update Operation: Changes the values of some attributes of a tulpe Select operation Unary operation
Select Operation: Uses some criteria to select some tuples from the original relation Project operation Unary operation Project Operation: Creates relation in which each tulpe has fewer attributes
Join operation Binary operation Join Operation: Takes two relation and combine them based on common attribute Union operation Binary operation
Union Operation: Creates new relation in which each tuple is either in the first relation, the second relation or in both Intersection operation Binary operation Intersection Operation: Creates new relation in which each tuple is either in both relations.
Difference operation Binary Operation Difference Operation: Creates new relation where the new tuples are in the first relation but not in the second. STRUCTURED
QUERY LANGUAGE SQL SQL is the standard language used for relational databases. It is declarative language where users declare what they want without having to write a step by stem procedure.
It was first implemented by Oracle Corporation 1. Insert SQL Insert Operation format insert into RELATION-NAME values (, , )
Insert (Example) insert into COURSES values (CIS52, TCP/IP Protocols, 6) 2. Delete SQL Delete Operation format delete from RELATION-NAME
where criteria Delete (Example) Delete from COURSES where No = CIS19
3. Update SQL Update Operation format update RELATION-NAME set attribute1 = value1 attribute 2 = value2 where criteria Update (Example)
update COURSES set unit = 6 where No = CIS51 4. Select SQL Select Operation format select *
from RELATION-NAME where criteria Select (Example) select * from COURSES where Unit = 5
5. Project SQL Project Operation format select from attribute-list RELATION-NAME Project (Example)
select from No, Unit COURSES 6. Join SQL Join Operation format
select attribute-list from RELATION NO1, RELATION NO2 where criteria Join (Example) select No, Course-Name, Unit, Professor from COURSES, TAUGHT-BY where COURSES.No = TAUGHT-BY.No;
7. Union SQL Union Operation format select from union select from
* RELATION NO1 * RELATION NO2 Union (Example) select from
union select from * CIS15-Roster * CIS52-Roster;
8. Intersection SQL Intersection Operation format select * from RELATION NO1 intersection select * from RELATION NO2 Intersection (Example)
select * from CIS15-Roster intersection select * from CIS52-Roster; 9. Difference SQL Difference Operation format
select from minus select from * RELATION NO1 *
RELATION NO2 Intersection (Example) select from minus select from
* CIS15-Roster * CIS52-Roster; OTHER DATABASE MODELS
Distributed Databases Based on the relational model Data are stored in several computers that communicate through the internet Data are either (1) fragmented or (2) replicated 1. Fragmented Distributed Databases
Data are localized; data are stored on local site Data can be accessed from different sites as well as the local site Although each site has complete control over its local data, there is global control through the internet 2. Replicated Distributed Database Each site holds an exact replica of another site
Any modification in one site is repeated at every site If the system fails in one site, the users at this site can access data at another site The levels of Data Database One or more tables
Table (relation) A collection of Records Record A group of related fields
Field One or more character Character At least 8 bits
Bit 0 or 1 Types of Database Program Are software tools used to create database. Examples of database programs are: 1.File Management Programs 2.Database Management System
Advanced Databases Data Warehouses and Data Mining A combination of smaller database that belong to the corporation Client/Server Database Systems Software programs used to respond to remote users request for information over the LAN. Server software runs on the server. Client software connects the user to server. The front end of the software is the part that interact with users. The back end refers to
the program code. To request information query language is used. Web-database integration Enables customers to proceed enquires over the net. Users dont have to use SQL. The web server accept the request and translates it to a query that is sent to the database over the internet 5 Characteristics of Good Database Data Integrity
Ensuring data is valid Data Independence Data is separated from software Avoiding data Redundancy
Repetition of input data is avoided Data Security Data is not accessible to unauthorized users Data Maintenance
Set procedures for adding ,deleting records for the purpose of optimization
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