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Transcript of Database Terms t DBMS –Database Management System. A software used to organise, analyse, store,...
![Page 1: Database Terms t DBMS –Database Management System. A software used to organise, analyse, store, retrieve, and edit information. –e.g., Visual FoxPro, Access.](https://reader035.fdocuments.us/reader035/viewer/2022062409/5697bff31a28abf838cbc8a3/html5/thumbnails/1.jpg)
Database Terms
DBMS– Database Management System. A software use
d to organise, analyse, store, retrieve, and edit information.
– e.g., Visual FoxPro, Access
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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.
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Database Terms
Record– a unit of storage in a database. In relational
database, the rows of table represent records.
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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”.
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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
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Database
namestud_id dob
WinnieF00111 {02/14/83}
AmyF00112 {03/16/82}
SteveF00007 {10/28/83}
AmyF00246 {08/25/82}
Field
Record
Key
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Database Design
Aims– to keep data integrity (correctness and
completeness) with the least for
• space• data duplication• updating efforts
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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
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Sample Address Book
Name:
Tele:
Address:
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Sample Address Book
Name
Tele
Field name
Char.
Char.
Data type
158
Width
ADDRBOOK.DBF
Address Char. 40
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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
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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
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Sample Student Report
SREPORT(stud_id, name, class,
sub_code, sub_desc, marks, ave_mk)
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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
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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
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Database Terms
Data Integrity (數據完整性 )– refers to the correctness and completeness o
f information in the database.
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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.
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Data Normalisation
First Normal Form (1NF)
Second Normal Form (2NF)
Third Normal Form (3NF)
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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.
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Sample Student Report
SREPORT(stud_id, name, class,
(sub_code, sub_desc, marks), ave_mk)
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Data Normalisation
Deriving 1NF
SREPORT(stud_id, name, class, ave_mk)
MARKS(stud_id, sub_code,
sub_desc, marks)
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Data Normalisation
Second Normal Form (2NF)– it is already in 1NF and if each non-key attribute
depends fully upon the key.
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Data Normalisation
SREPORT(stud_id, name, class, ave_mk)
MARKS(stud_id, sub_code,
sub_desc, marks)
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Data Normalisation
Deriving 2NF
SREPORT(stud_id, name, class, ave_mk)
MARKS(stud_id, sub_code, marks)
SUBJECT(sub_code, sub_desc)
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Data Normalisation
Third Normal Form (3NF)– it is already in 2NF and if there is no dependency
between non-key attribute.
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Data Normalisation
Deriving 3NF
SREPORT(stud_id, name, class, ave_mk)
MARKS(stud_id, sub_code, marks)
SUBJECT(sub_code, sub_desc)
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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
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Data Normalisation
Invoice(Inv_no, Cust_no, Cust_Addr,
Inv_date, (Item_code, Item_desc,
Item_price, Qty, Price), Total)
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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)
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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)
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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)
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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.
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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.
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Database Terms
Data Independence– refers to the data in a database which is
separated from the application programs that manipulate it.