Database Terms

DBMS– Database Management System. A software use

d to organise, analyse, store, retrieve, and edit information.

– e.g., Visual FoxPro, Access

Database Terms

Database– collection of data organised for storage in a co

mputer memory. In relational database, information are stored in the form of table.

Database Terms

Record– a unit of storage in a database. In relational

database, the rows of table represent records.

Database Terms

Field– a data unit in a record. In relational database,

the columns of table represent fields. Since fields have different characteristics (numeric, character, date, etc.), they are also called “attributes”.

Database Terms

Key– a KEY is used to uniquely identify a record in

the database.

– a KEY can be a single field or combination of fields

Database

namestud_id dob

WinnieF00111 {02/14/83}

AmyF00112 {03/16/82}

SteveF00007 {10/28/83}

AmyF00246 {08/25/82}

Field

Record

Key

Database Design

Aims– to keep data integrity (correctness and

completeness) with the least for

• space• data duplication• updating efforts

Database Design

Basic design– there must exist a KEY that uniquely determines

the entire record

– e.g., student identity that uniquely determines a student record

Sample Address Book

Name:

Tele:

Address:

Sample Address Book

Name

Tele

Field name

Char.

Char.

Data type

158

Width

ADDRBOOK.DBF

Address Char. 40

Sample Student Report

Student ID: f99007 Student Name: Wong Siu Fu

Average Mark: 60.25

Subject Code Subject Description. Marks

C01

E01

Chinese

English 62.00

64.00

M01 Mathematics...

86.00...

.

.

.

Class: 6F

Sample Student Report

stud_id

name

sub_code

sub_descmarks

ave_mk

Field name

Char.

Char.

Char.

Char.

Numeric

Numeric

Data type

6

25

3

15

3

6 (2 d.p.)

Width

SREPORT.DBF

class Char. 2

Sample Student Report

SREPORT(stud_id, name, class,

sub_code, sub_desc, marks, ave_mk)

Sample Student Report

Student ID: f99008 Student Name: Po King Wan

Average Mark: 60.25

Subject Code Subject Description. Marks

C01

E01

Chinese

English 60.00

66.00

M01 Mathematics...

72.00...

.

.

.

Class: 6F

Database Terms

Data Redundancy (冗餘數據 )– same data item exists in one or more databases.

– Disadvantage:• duplication causes wasted storage space• efforts to maintain common data up-to-date

Database Terms

Data Integrity (數據完整性 )– refers to the correctness and completeness o

f information in the database.

Data Normalisation

a step-by-step process that is used to decompose a database into two or more databases

in order to avoid side effects during the operation of a database involving insertion, deletion and updating records.

Data Normalisation

First Normal Form (1NF)

Second Normal Form (2NF)

Third Normal Form (3NF)

Data Normalisation

First Normal Form (1NF)– if every attribute is based upon a simple, unique

value, i.e., there are no repeating groups of attribute types.

Sample Student Report

SREPORT(stud_id, name, class,

(sub_code, sub_desc, marks), ave_mk)

Data Normalisation

Deriving 1NF

SREPORT(stud_id, name, class, ave_mk)

MARKS(stud_id, sub_code,

sub_desc, marks)

Data Normalisation

Second Normal Form (2NF)– it is already in 1NF and if each non-key attribute

depends fully upon the key.

Data Normalisation

SREPORT(stud_id, name, class, ave_mk)

MARKS(stud_id, sub_code,

sub_desc, marks)

Data Normalisation

Deriving 2NF

SREPORT(stud_id, name, class, ave_mk)

MARKS(stud_id, sub_code, marks)

SUBJECT(sub_code, sub_desc)

Data Normalisation

Third Normal Form (3NF)– it is already in 2NF and if there is no dependency

between non-key attribute.

Data Normalisation

Deriving 3NF

SREPORT(stud_id, name, class, ave_mk)

MARKS(stud_id, sub_code, marks)

SUBJECT(sub_code, sub_desc)

Sample Invoice

INVOICE NUMBER: 100486-300

Customer Number: C12345Customer Address: Hang Shin LinkInvoice Date: 04/01/99

Item Code Item Desc. Item Price Quantity Price

Total:

1123

1246

Chocolate

Coke

8.00

5.00

2

12 60.00

16.00

76.00

Data Normalisation

Invoice(Inv_no, Cust_no, Cust_Addr,

Inv_date, (Item_code, Item_desc,

Item_price, Qty, Price), Total)

Data Normalisation

Deriving 1NF

Invoice(Inv_no, Cust_no, Cust_Addr,

Inv_date, Total)

ItemDetails(Inv_no, Item_code, Item_desc,

Item_price, Qty, Price)

Data Normalisation

Deriving 2NF

Invoice(Inv_no, Cust_no, Cust_Addr,

Inv_date, Total)

ItemDetails(Inv_no, Item_code, Qty, Price)

Items(Item_code, Item_desc, Item_price)

Data Normalisation

Deriving 3NF

Invoice(Inv_no, Cust_no, Inv_date, Total)

Customer(Cust_no, Cust_Addr)

ItemDetails(Inv_no, Item_code, Qty, Price)

Items(Item_code, Item_desc, Item_price)

Partial Dependence

ItemDetails(Inv_no, Item_code,

Item_desc, Item_price, Qty, Price)

The non-key fields “Item_desc” and “Item_price” is dependent partly on the key, i.e., “Item_code”. This is known as partial dependence.

Transitive Dependence

Invoice(Inv_no, Cust_no, Cust_Addr,

Inv_date, Total)

The non-key field “Cust_Addr” is dependent on the non-key field “Cust_no”, this is known as transitive dependence.

Database Terms

Data Independence– refers to the data in a database which is

separated from the application programs that manipulate it.