Understanding Databases: From Lists to Relational Database Systems and SQL, Appunti di Informatica

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The database is a collection of information organized in related tables of data and definitions of data objects. Data in a database can be easily accessed and manipulated through the computer program. The purpose of a database is:

• (^) To store data
• (^) To provide an organizational structure for data
• (^) To provide a mechanism for querying, creating, modifying and deleting data A database can store information and relationships that are more complicated than a simple list

Relational database

A relational database stores information in tables. Each informational theme is stored in its own table A relational database will break-up a list into several parts

• One part for each theme in the list

• for example, a project list might be divided

into a COSTUMER Table, a PROJECT Table and a PRPJECT_MANAGER Table

Relational database and Lists

Pros and Cons

• a relational database minimizes

data redundancy, preserves complex relationships among topics and allows for partial data

• A relational database provides a

solid foundation for creating user interface forms and reports

• A^ relational^ database^ is

more complicated than a list

Database

systems

The four components of a database system are:

• Users

• Database applications

• Database management

system (DBMS)

• Database

Users

A user of a database system will:

• Use^ a^ database^ application^ to^ keep

track of information

• Use different user interface forms to

enter, read, delete and query data

• Produce reports

Database

manageme

nt system

A database management system (DBMS) serves as an intermediary between database applications and the database The DBMS manages and controls database activities The DBMS create, processes and administers the database it controls

Functions

of a

DBMS

Create databases Create tables Create supporting structures Read database data Modify database data (insert, update, delete) Maintain database structures Enforce rules Control concurrency Provide security Perform data backup and recovery

Personal database system

Personal database systems typically:

• Support one application

• Have only a few tables

• Are simple in design

• Involve only one computer

• Support one user at a time

Enterprise-level

database systems

Enterprise-level database systems typically:

• Support several users simultaneously
• Support more than one application
• Involve multiple computers
• Are complex in design
• Have many tables
• Have^ many databases