Basic Concepts of Database

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Database definition

• In general, a database is anything that stores data– Example, a phone book which store name &

phone number• In computer, a database refers to

– collection of organized data to be accessed, retrieved and used

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Function of a database in general

• Allow anyone to:– store (add)– delete (remove)– organize– use– present data

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Example: data in Access database

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What is a DBMS?

• Database Management System is a software that store and manage database

• It allows to:• create databases• insert, update and delete data• sort and query data• create forms and reports

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Examples of DBMS

•Microsoft Access, MySQL, PostgreSQL, SQL Server, Oracle, dBASE, Clipper and FoxPro

• Examples of DBMS applications: Automated teller machineComputerized Library SystemFlight Reservation SystemStaff Information SystemStudents System

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DBMS Models

• DBMS Model describe:– rules and standards on how database organize data– defines how users view organization of data

• Common models include: (remember)– Hierarchical model– Network model – Object-oriented model – Relational model

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Hierarchical Model

• organizes data in a tree structure• all access to data starts at the top of the hierarchy

and moves downward– for example, from customer to orders, vendor to

purchases, etc• there is a hierarchy of parent and child data

segments• support one to many relationship

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Network Model• Similar like hierarchical model but

– permit more than one parent per child– thus permit the modeling of many-to-many relationships in data

• Organizes data using two fundamental constructs, called records and sets

• Records contain fields , sets define one-to-many relationships between records: one owner, many members

• Very flexible• Not widely use

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Object Oriented Model• based on a collection of objects• an object contains:

– values stored in instance variables within the object– bodies of code called methods that operate on the object

• for example, consider an object representing a bank account– The object contains instance variables number and balance.– The object contains a method pay-interest which adds interest to the balance.– Under most data models, changing the interest rate entails changing code in

application programs.– In the object-oriented model, this only entails a change within the pay-

interest method.• Diverse structures• Can execute complex analytical and data manipulation operations

to search and transform multimedia and other complex objects

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Relational Model• Data is stored in two-dimensional tables (rows and

columns)• Widely used• Example, Microsoft Access and MySQL

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Data Hierarchy

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Database File

Table

Record

Database File: Physical file stored in a storage media. Example: StudentDB.accdb

Table: Contain information on a specific subject / topic. Example: Student, Courses

Record: Contain information on single data item in a table. Example: information about a student. Also known as row in a table.

Field: Contain a specific piece of information within a record. Example: Student Name, Student IC. Also known as column in a table.

Definition- systematic organization of data, often in a hierarchical form

Field

Example of an Access table

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fields

records

Relational database

• stores data in tables• tables are organized into columns, and each

column stores one type of data• data for a single “instance” of a table is stored as a

row

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What is RDBMS?• RDBMS is a DBMS which manages a relational

database– Example, Microsoft Access and MySQL

• Data is structured in tables, records and fields• Each table consists of rows (records)• Each table row consists of one or more fields

(columns)• RDBMS store the data into collection of tables,

which might be related by common fields15

Advantages of RDBMS• Minimum data redundancy• Data consistency - less likelihood of incorrect or

incomplete data being stored or used• Integrated data – data is organized in logical relationship

thus making it easy to relate data items• Data sharing – allows users from different department

to share data• Data accessibility – allows users to access or retrieve in a

flexible manner• Uniform security, privacy and integrity control – db

administrator can establish control for accessing, updating and protecting the data

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Categories of RDBMS

• Personal database– Best in single-user environment (up to 10 users)– Example: Microsoft Access

• Client/Server database– Support multiple users in a network environment– Run in a server, client can request data from the server &

query, update & report locally– Example: SQL Server

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Master table

• Contains a primary key (must be unique as a password)

• Normally is a table that lists the properties of things that have some permanence and used many times in other tables

• Example customers, teachers, students and subjects offered

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Transaction table• Records some kind of interaction or event between master

tables• Transaction tables are typically used in posting operations

or as lookup tables• Example,

– In Student Information System, the actual classes taken by students are transactions because they record specific interactions between students and teachers

– In an eCommerce software the shopping cart tables are all transaction tables, they record the purchase of items by customers

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Primary Key

• Field, or fields, which by itself, or together uniquely identify each row in a table

• Used to match up records in different tables• Usually indexed• Help to define the relationships between tables

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Primary Key• Requirement: must be unique and cannot be

empty or null• Functions:

• Used to associate data from multiple tables• Prevent duplicate record• Control the order of records• Faster to locate records

• Possible to have 2 or more fields as primary key in a table –this is called composite key

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Foreign Key

• Same data field and type which is linked to a primary key in a corresponding table

• Example:– In SalesTransaction table below, CustomerID would be the

Foreign Key field– The Foreign Key is used to look up the CustomerID in the

Customer table where the CustomerID is the primary key

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Customer table

CustomerID (PRIMARY KEY)

CustomerName

SalesTransaction table

SalesID

SalesDate

CustomerID (FOREIGN KEY)

Relationships• Relationships establishes the association between

common fields in two tables• Common field links two tables to each other, thus

ensuring connection between the data in the tables within the same database

• REMEMBER: Access uses related tables - one table can find and use data in another table

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What will we learn in this subject?

• Access objects – Table, Query, Form, Report, Macro

• Switchboard (is also a form)• SQL

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