Staffsite STMIK PPKIA Pradnya Paramita DD_5_2
Database Design
5-2
Relationship Types
Copyright © 2015, Oracle and/or its affiliates. All rights reserved.
Objectives
This lesson covers the following objectives:
• Recognize and give examples of a one-to-one relationship
• Recognize and give examples of a one-to-many relationship
• Recognize and give examples of a many-to-many relationship
• Recognize redundant relationships and remove them from
the ERD
DDS5L2
Relationship Types
Copyright © 2015, Oracle and/or its affiliates. All rights reserved.
3
Purpose
• Can one PERSON own many DVDs, or only one ?
• Can one DVD be owned by many PERSONs?
• As we refine and improve our model, we want to make sure
our entity relationships correctly model our business rules.
• Remember, you can avoid future costly mistakes by thinking
through the details early on.
DDS5L2
Relationship Types
Copyright © 2015, Oracle and/or its affiliates. All rights reserved.
4
One-to-Many (1:M) Relationships
• The various types of 1:M
relationships are most common
in an ER Model.
Relationship Types
1:M
• You have seen several examples
already.
EMPLOYEE
DEPARTMENT
assigned to
responsible for
1:M Relationship
DDS5L2
Relationship Types
Copyright © 2015, Oracle and/or its affiliates. All rights reserved.
5
Many-to-Many (M:M) Relationships
• The various types of M:M
relationships are common,
particularly in a first version of
an ER model.
Relationship Types
M:M
• In later stages of the modeling
process, all M:M relationships
will be resolved, and
disappear.
STUDENT
learns from
TEACHER
educates
M:M Relationships
DDS5L2
Relationship Types
Copyright © 2015, Oracle and/or its affiliates. All rights reserved.
6
One-to-One Relationships For Roles
Relationship Types
1:1
• Usually you will find
just a few of the
various types of 1:1
relationships in every
ER model.
• Mandatory at one end
of the 1:1 relationship
commonly occurs when
roles are modeled.
PERSON
acting as
TEACHER
role of
acting as
STUDENT
role of
1:1 Relationships
DDS5L2
Relationship Types
Copyright © 2015, Oracle and/or its affiliates. All rights reserved.
7
One-to-One Relationships For Processes
• 1:1 relationships (of all three variations) also occur when
some of the entities represent various stages in a process.
evaluated with
EXAM
ANSWER KEY
for
the basis for
RECIPE
DISH
the result
1:1 Process Relationships
DDS5L2
Relationship Types
Copyright © 2015, Oracle and/or its affiliates. All rights reserved.
8
Redundant Relationships
• A redundant relationship can be
derived from another relationship
in the model.
• In this example, you can derive
the relationship from PERSON to
COUNTRY from the other two
relationships (COUNTRY to TOWN,
TOWN to PERSON), so you should
remove the direct relationship
from COUNTRY to PERSON .
DDS5L2
Relationship Types
COUNTRY
location of
location of
located in
TOWN
hometown of
living in
living in
PERSON
Copyright © 2015, Oracle and/or its affiliates. All rights reserved.
9
Redundant Relationships
• However, be careful of
concluding that a relationship
is redundant based on the
structure alone.
• Read the relationships to
check.
• The ERD shown here does not
reflect a redundant
relationship.
COUNTRY
location of
located
in
the birthplace
of
TOWN
hometown
living
born in
PERSON
DDS5L2
Relationship Types
Copyright © 2015, Oracle and/or its affiliates. All rights reserved.
10
Terminology
Key terms used in this lesson included:
• Many-to-many (M:M)
• One-to-many (1:M)
• One-to-one (1:1)
• Redundant
DDS5L2
Relationship Types
Copyright © 2015, Oracle and/or its affiliates. All rights reserved.
11
Summary
In this lesson, you should have learned how to:
• Recognize and give examples of a one-to-one relationship
• Recognize and give examples of a one-to-many relationship
• Recognize and give examples of a many-to-many relationship
• Recognize redundant relationships and remove them from
the ERD
DDS5L2
Relationship Types
Copyright © 2015, Oracle and/or its affiliates. All rights reserved.
12
5-2
Relationship Types
Copyright © 2015, Oracle and/or its affiliates. All rights reserved.
Objectives
This lesson covers the following objectives:
• Recognize and give examples of a one-to-one relationship
• Recognize and give examples of a one-to-many relationship
• Recognize and give examples of a many-to-many relationship
• Recognize redundant relationships and remove them from
the ERD
DDS5L2
Relationship Types
Copyright © 2015, Oracle and/or its affiliates. All rights reserved.
3
Purpose
• Can one PERSON own many DVDs, or only one ?
• Can one DVD be owned by many PERSONs?
• As we refine and improve our model, we want to make sure
our entity relationships correctly model our business rules.
• Remember, you can avoid future costly mistakes by thinking
through the details early on.
DDS5L2
Relationship Types
Copyright © 2015, Oracle and/or its affiliates. All rights reserved.
4
One-to-Many (1:M) Relationships
• The various types of 1:M
relationships are most common
in an ER Model.
Relationship Types
1:M
• You have seen several examples
already.
EMPLOYEE
DEPARTMENT
assigned to
responsible for
1:M Relationship
DDS5L2
Relationship Types
Copyright © 2015, Oracle and/or its affiliates. All rights reserved.
5
Many-to-Many (M:M) Relationships
• The various types of M:M
relationships are common,
particularly in a first version of
an ER model.
Relationship Types
M:M
• In later stages of the modeling
process, all M:M relationships
will be resolved, and
disappear.
STUDENT
learns from
TEACHER
educates
M:M Relationships
DDS5L2
Relationship Types
Copyright © 2015, Oracle and/or its affiliates. All rights reserved.
6
One-to-One Relationships For Roles
Relationship Types
1:1
• Usually you will find
just a few of the
various types of 1:1
relationships in every
ER model.
• Mandatory at one end
of the 1:1 relationship
commonly occurs when
roles are modeled.
PERSON
acting as
TEACHER
role of
acting as
STUDENT
role of
1:1 Relationships
DDS5L2
Relationship Types
Copyright © 2015, Oracle and/or its affiliates. All rights reserved.
7
One-to-One Relationships For Processes
• 1:1 relationships (of all three variations) also occur when
some of the entities represent various stages in a process.
evaluated with
EXAM
ANSWER KEY
for
the basis for
RECIPE
DISH
the result
1:1 Process Relationships
DDS5L2
Relationship Types
Copyright © 2015, Oracle and/or its affiliates. All rights reserved.
8
Redundant Relationships
• A redundant relationship can be
derived from another relationship
in the model.
• In this example, you can derive
the relationship from PERSON to
COUNTRY from the other two
relationships (COUNTRY to TOWN,
TOWN to PERSON), so you should
remove the direct relationship
from COUNTRY to PERSON .
DDS5L2
Relationship Types
COUNTRY
location of
location of
located in
TOWN
hometown of
living in
living in
PERSON
Copyright © 2015, Oracle and/or its affiliates. All rights reserved.
9
Redundant Relationships
• However, be careful of
concluding that a relationship
is redundant based on the
structure alone.
• Read the relationships to
check.
• The ERD shown here does not
reflect a redundant
relationship.
COUNTRY
location of
located
in
the birthplace
of
TOWN
hometown
living
born in
PERSON
DDS5L2
Relationship Types
Copyright © 2015, Oracle and/or its affiliates. All rights reserved.
10
Terminology
Key terms used in this lesson included:
• Many-to-many (M:M)
• One-to-many (1:M)
• One-to-one (1:1)
• Redundant
DDS5L2
Relationship Types
Copyright © 2015, Oracle and/or its affiliates. All rights reserved.
11
Summary
In this lesson, you should have learned how to:
• Recognize and give examples of a one-to-one relationship
• Recognize and give examples of a one-to-many relationship
• Recognize and give examples of a many-to-many relationship
• Recognize redundant relationships and remove them from
the ERD
DDS5L2
Relationship Types
Copyright © 2015, Oracle and/or its affiliates. All rights reserved.
12