6.8 Case Study:
E-R for Supplier-and-Parts Database
Unit 6 Database Design and the E-R
Model
6-1
Supplier-and-Parts Database

Supplier-and-Parts Database
<e.g.> Supplier-and-Parts Database
S
P
S# SNAME STATUS CITY
S1 Smith
20
London
S2 Jones
10
Paris
S3 Blake
30
Paris
S4 Clark
20
London
S5 Adams
30
Athens
P# PNAME
P1 Nut
P2 Bolt
P3 Screw
P4 Screw
P5 Cam
P6 Cog
Wei-Pang Yang, Information Management, NDHU
COLOR
Red
Green
Blue
Red
Blue
Red
WEIGHT CITY
12
London
17
Paris
17
Rome
14
London
12
Paris
19
London
SP
S# P# QTY
S1 P1 300
S1 P2 200
S1 P3 400
S1 P4 200
S1 P5 100
S1 P6 100
S2 P1 300
S2 P2 400
S3 P2 200
S4 P2 200
S4 P4 300
S4 P5 400
Unit 6 Database Design and the E-R
Model
6-2
Entity/Relationship Diagram
Regular
Entity
<e.g>
Weak
Entity
...
Department
Dependent
1
 Property:
Base
...
First
Department_Emp
Derived
M
Emp_Dependent
Ename
M
Multi
1
Employee
Emp#
Key
Last
MI
Composite
Salary
...
 Entity :
M
1
Proj_Work
Proj_Mngr
 Relationship:
M
M
Project
P#
Regular
Weak
total
partial
...
Part
Exp M M Imp
S#
Qty
M
M
SPJ
M
M
Sname
Supplier
Status
City
SP
Part_Struct
Qty
Qty
Wei-Pang Yang, Information Management, NDHU
Unit 6 Database Design and the E-R
Model
6-3
Semantic Concepts
 Entity: a thing which can be distinctly identified. e.g. S, P
• Weak Entities: an entity that is existence-dependent
on some other entity. e.g. Dependent
• Regular Entities: an entity that is not weak.
 Property:
• Simple or Composite Property
• key: unique value
• Single or
Multi-valued: i.e. repeating data
• Missing: unknown or not applicable.
• Base or
Derived: e.g. "total quantity"
Wei-Pang Yang, Information Management, NDHU
Unit 6 Database Design and the E-R
Model
6-4
Semantic Concepts (cont.)
 Relationship: association among entities.
• participant: the entity participates
Dependent
M
in a relationship.
e.g. Employee, Dependent
1
• degree of relationship:
number of participants.
• total participant:
every instance is used.
e.g. Dependent
• partial participant:
e.g. Employee
Employee
Employee
E1
E2
E3
E4
.
.
.
.
Dependent
.
.
.
.
Note: An E/R relationship can be one-to-one, one-tomany, many-to-one, or many-to-many.
Wei-Pang Yang, Information Management, NDHU
Unit 6 Database Design and the E-R
Model
6-5
Semantic Concepts (cont.)
 Subtype: Any given entity can be a subtype of other entity.
e.g. An example type hierarchy:
Employee
Programmer
Application
Programmer
System
Programmer
• Programmer  Employee
• Application Programmer  Programmer
Wei-Pang Yang, Information Management, NDHU
Unit 6 Database Design and the E-R
Model
6-6
Transfer E-R Diagram to SQL Definition
ER-Diagram
(1) Regular Entities  Base Relations
 e.g. Department DEPT
Employee EMP
Supplier S
Part P
Project J
 attributes: properties.
 primary key: key property.
<e.g> CREATE TABLE EMP
SQL Definition
(EMP# ......
..
.
primary key (EMP#));
..
.
(2) Properties  attributes
 multivalued property: normalized first.
Wei-Pang Yang, Information Management, NDHU
Unit 6 Database Design and the E-R
Model
6-7
Transfer E-R Diagram to SQL Definition (cont.)
(3) Many-to-Many Relationships
Base Relations
P#
S#
M
P
<e.g.> Consider
SUPP-PART SP
<e.g.> CREATE
– primary key:
(1) combination of foreign keys, or
(2) introduce a new attribute.
ID
1
2
3
...
Wei-Pang Yang, Information Management, NDHU
M
S
QTY
– foreign keys:
key attributes of the participant entity.
– attributes:
primary key  foreign keys
properties
SP
S#
P#
QTY
TABLE SP
( S#, ...,
P#, ...,
Qty, ...,
FOREIGN KEY (S#) REFERENCES S
NULL NOT ALLOWED
DELETE OF S RESTRICTED
UPDATE OF S.S# CASCADES
FOREIGN KEY (P#) REFERENCES P
......
PRIMARY KEY (S#, P#) )
Unit 6 Database Design and the E-R
Model
6-8
Transfer E-R Diagram to SQL Definition (cont.)
(4) Many-to-One or
One-to-Many or
One-to-One Relationships
→ 不用給Base-Relation, 但….
DEPT#
e.g. Consider
DEPT_EMP(Department_Employee)
DEPT_EMP
1° no any new relation is necessary.
2° Introduce a foreign key in "many" side relation
(eg. EMP) that reference the "one" side
relation (eg. DEPT).
Department
(DEPT)
1
M
EMP#
Employee
(EMP)
DEPT#
CREATE TABLE EMP
( EMP#, ...
DEPT#, ...
......
FOREIGN KEY (DEPT#) REFERENCES DEPT
......
);
Wei-Pang Yang, Information Management, NDHU
Unit 6 Database Design and the E-R
Model
6-9
Transfer E-R Diagram to SQL Definition (cont.)
(5) Weak Entities  Base Relation + Foreign Key
• foreign key: key property of its dependent entity
e.g. EMP#
• primary key:
e.g. name
name
(1) combination of foreign key and its own primary key
EMP#
(2) introduce a new attribute
e.g. CREATE
TABLE DEPENDENT
Dependent
M
( EMP#, …
1
name,
EMP
......
EMP#
FOREIGN KEY (EMP#) REFERENCES EMP
NULL NOT ALLOWED
DELETE OF EMP CASCADES
UPDATE OF EMP.EMP# CASCADES
PRIMARY KEY ( EMP#, DEPENDENT_NAME ) );
Wei-Pang Yang, Information Management, NDHU
Unit 6 Database Design and the E-R
Model
6-10
Transfer E-R Diagram to SQL Definition (cont.)
(6) Supertypes and SubtypesBase Relation + Foreign Key
<e.g.> CREATE TABLE EMP
( EMP#, ...
DEPT#, ...
SALARY, ...
......
PRIMARY KEY (EMP#), ...);
EMP
PGMR
CREATE TABLE PGMR
( EMP#, ...
LANG#, ...
SALARY, ...
......
PRIMARY KEY (EMP#)
FOREIGN KEY (EMP#) REFERENCES EMP
......);
Wei-Pang Yang, Information Management, NDHU
Unit 6 Database Design and the E-R
Model
6-11
17.7 The Entity/Relationship Model
 Proposed by Peter Pin-Shan Chen. “The Entity-
Relationship Model,” in ACM Trans. on Database
System Vol. 1, No. 1, pp.9-36, 1976.
 E-R Model contains:
• Semantic Concepts and
• E/R Diagram.
17-12
Entity/Relationship Diagram
Regular
Entity
<e.g>
Weak
Entity
...
Department
Dependent
1
 Property:
Base
...
First
Department_Emp
Derived
M
Emp_Dependent
Ename
M
Multi
1
Employee
Emp#
Key
Last
MI
Composite
Salary
...
 Entity :
M
1
Proj_Work
Proj_Mngr
 Relationship:
M
M
Project
Regular
Weak
total
partial
P#
...
Part
Exp M M Imp
S#
Qty
M
M
SPJ
M
M
Sname
Supplier
Status
City
SP
Part_Struct
Qty
Qty
Wei-Pang Yang, Information Management, NDHU
17-13
Semantic Concepts
 Entity: a thing which can be distinctly identified. e.g. S, P
• Weak Entities: an entity that is existence-dependent
on some other entity. e.g. Dependent
• Regular Entities: an entity that is not weak.
 Property:
• Simple or Composite Property
• key: unique value
• Single or
Multi-valued: i.e. repeating data
• Missing: unknown or not applicable.
• Base or
Derived: e.g. "total quantity"
Wei-Pang Yang, Information Management, NDHU
17-14
Semantic Concepts (cont.)
 Relationship: association among entities.
• participant: the entity participates
Dependent
M
in a relationship.
e.g. Employee, Dependent
1
• degree of relationship:
number of participants.
• total participant:
every instance is used.
e.g. Dependent
• partial participant:
e.g. Employee
Employee
Employee
E1
E2
E3
E4
.
.
.
.
Dependent
.
.
.
.
Note: An E/R relationship can be one-to-one, one-tomany, many-to-one, or many-to-many.
Wei-Pang Yang, Information Management, NDHU
17-15
Semantic Concepts (cont.)
 Subtype: Any given entity can be a subtype of other entity.
e.g. An example type hierarchy:
Employee
Programmer
Application
Programmer
System
Programmer
• Programmer  Employee
• Application Programmer  Programmer
Wei-Pang Yang, Information Management, NDHU
17-16
Transfer E-R Diagram to SQL Definition
ER-Diagram
(1) Regular Entities  Base Relations
 e.g. Department DEPT
Employee EMP
Supplier S
Part P
Project J
 attributes: properties.
 primary key: key property.
<e.g> CREATE TABLE EMP
SQL Definition
(EMP# ......
..
.
primary key (EMP#));
..
.
(2) Properties  attributes
 multivalued property: normalized first.
Wei-Pang Yang, Information Management, NDHU
17-17
Transfer E-R Diagram to SQL Definition (cont.)
(3) Many-to-Many Relationships
Base Relations
P#
S#
M
P
<e.g.> Consider
SUPP-PART SP
<e.g.> CREATE
– primary key:
(1) combination of foreign keys, or
(2) introduce a new attribute.
ID
1
2
3
...
Wei-Pang Yang, Information Management, NDHU
M
S
QTY
– foreign keys:
key attributes of the participant entity.
– attributes:
primary key  foreign keys
properties
SP
S#
P#
QTY
TABLE SP
( S#, ...,
P#, ...,
Qty, ...,
FOREIGN KEY (S#) REFERENCES S
NULL NOT ALLOWED
DELETE OF S RESTRICTED
UPDATE OF S.S# CASCADES
FOREIGN KEY (P#) REFERENCES P
......
PRIMARY KEY (S#, P#) )
17-18
Transfer E-R Diagram to SQL Definition (cont.)
(4) Many-to-One or
One-to-Many or
One-to-One Relationships
→ 不用給Base-Relation, 但….
DEPT#
e.g. Consider
DEPT_EMP(Department_Employee)
DEPT_EMP
1° no any new relation is necessary.
2° Introduce a foreign key in "many" side relation
(eg. EMP) that reference the "one" side
relation (eg. DEPT).
Department
(DEPT)
1
M
EMP#
Employee
(EMP)
DEPT#
CREATE TABLE EMP
( EMP#, ...
DEPT#, ...
......
FOREIGN KEY (DEPT#) REFERENCES DEPT
......
);
Wei-Pang Yang, Information Management, NDHU
17-19
Transfer E-R Diagram to SQL Definition (cont.)
(5) Weak Entities  Base Relation + Foreign Key
• foreign key: key property of its dependent entity
• primary key:
e.g. EMP#
e.g. name
name
(1) combination of foreign key and its own primary key
(2) introduce a new attribute
EMP#
Dependent
e.g. CREATE
TABLE DEPENDENT
M
( EMP#, …
name,
1
......
EMP
EMP#
FOREIGN KEY (EMP#) REFERENCES EMP
NULL NOT ALLOWED
DELETE OF EMP CASCADES
UPDATE OF EMP.EMP# CASCADES
PRIMARY KEY ( EMP#, DEPENDENT_NAME ) );
Wei-Pang Yang, Information Management, NDHU
17-20
Transfer E-R Diagram to SQL Definition (cont.)
(6) Supertypes and SubtypesBase Relation + Foreign Key
<e.g.> CREATE TABLE EMP
( EMP#, ...
DEPT#, ...
SALARY, ...
......
PRIMARY KEY (EMP#), ...);
EMP
PGMR
CREATE TABLE PGMR
( EMP#, ...
LANG#, ...
SALARY, ...
......
PRIMARY KEY (EMP#)
FOREIGN KEY (EMP#) REFERENCES EMP
......);
Wei-Pang Yang, Information Management, NDHU
17-21
Home Work: Term Project

Design and implementation an useful, complete, and “real”
database system.

Steps:
 Take any data you are familiar with. (from your work or ?)
 System Analysis represented by flow chart
 By using the E-R model to analysis and describe your data.
 Design logical database, user interface, and more
 Design the database system as “complete and real” as possible.

Due:
 Demo and
 A Comprehensive Report
Wei-Pang Yang, Information Management, NDHU
17-22
end of unit 17
Wei-Pang Yang, Information Management, NDHU