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Basic Database Concepts

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Basic Database Concepts
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Basic Database Concepts

What is data ?

• Data is raw, unorganized facts that need to be processed

Example :• Each student's grade score is one piece of

data.

What is Information?

• When data is processed, organized, structured or presented in a given context so as to make it useful, it is called information.

Example: • GPA or CGPA of a student.

What is database?

• A database is a collection of information that is organized so that it can easily be accessed, managed, and updated.

Databases

• Bank accounts• Stock control• Personnel systems• Product catalogues• Telephone directories• Credit card details• Student records• Stock market prices• Discussion boards

Database Users

• End users – Use the database system to achieve some goal

• Application developers – Write software to allow end users to interface

with the database system

• Database Administrator (DBA)– Designs & manages the database system

• Database systems programmer– Writes the database software itself

Database Management Systems

• A database is a collection of information• A database management system (DBMS) is the

software than controls that information

• Examples:– Oracle– DB2 (IBM)– MS SQL Server– MS Access– Ingres– PostgreSQL– MySQL

What the DBMS does

• Provides users with

– Data definition language (DDL)– Data manipulation language (DML)– Data control language (DCL)

• DBMS provides

– Persistence– Concurrency– Integrity– Security– Data independence

• Data Dictionary

– Describes the database itself

Data Dictionary - Metadata

• The dictionary stores information about the database itself

• This is data about data or ‘metadata’• Almost every aspect of the DBMS uses the

dictionary

Metadata

• The dictionary holds– Descriptions of database objects (tables, users,

rules, views, indexes,…)– Information about who is using which data (locks)– Schemas and mappings

File Based Systems

• File based systems– Data is stored in files– Each file has a specific format– Programs that use these files depend on

knowledge about that format

• Problems:– No standards– Data duplication– Data dependence– No way to generate ad hoc queries– No provision for security, recovery, concurrency,

etc.

Relational Systems

• Information is stored as tuples or records in relations or tables• There is a sound mathematical theory of relations• Most modern DBMS are based on the relational model

• The relational model covers 3 areas:– Data structure– Data integrity– Data manipulation

• More details in the next lecture…

Tables

• Relational databases views all data in the form of tables• Each column represents an attribute, e.g. the Customer table

has attributes ID, Name, Address..etc.• Relationships between entities are represented by values

stored in columns of the corresponding tables, e.g. Customer_ID is an attribute of both the Customer table and the Order table. This makes it easy to link an order with its customer.

Fig. (b) Product and Customer tables

Fig. (a) Order and Order_Line tables

The range ofdatabase applications

• Personal Database PCs/PDAs, Cell phones• Workgroup Database. Designed to support collaboration in a

small team (less than 25 people)• Department Database typically larger than a workgroup (25-

100 people) and more diverse range of functions – e.g. personnel database

• Enterprise Database – scope of the whole organization. May be more than one, as a single database for a large organization may be impractical due to performance difficulties for large databases, diverse needs of user groups, and difficulty of achieving common definition of data (metadata) for all users.


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