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ITEC 3220A Using and Designing Database Systems. Instructor: Gordon Turpin Course Website: www.cse.yorku.ca/~gordon/itec3220S07 Office: CSEB3020. Supertypes and Subtypes. Generalization hierarchy: depicts relationships between higher-level supertype and lower-level subtype entities - PowerPoint PPT Presentation
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ITEC 3220AUsing and Designing Database Systems
Instructor: Gordon TurpinCourse Website: www.cse.yorku.ca/~gordon/itec3220S07 Office: CSEB3020
2
Supertypes and Subtypes
• Generalization hierarchy: depicts relationships between higher-level supertype and lower-level subtype entities
• Supertype:Supertype: contains the shared attributes
• Subtype:Subtype: contains the unique attributes• Inheritance:Inheritance:
– Subtype entities inherit values of all attributes of the supertype
– An instance of a subtype is also an instance of the supertype
3
Supertypes and Subtypes (Cont’d)
Supertype/ subtype relationships
SUPERTYPE
Attributes shared by all entities
SUBTYPE1
Attributes unique to subtype2
SUBTYPE2
Attributes unique to subtype1
General entity type
And so forth
Specialized version of supertype
4
Supertypes and Subtypes (Cont’d)
• Disjoint relationships– Unique subtypes– Non-overlapping– Indicated with a ‘G’
• Overlapping subtypes– An instance of the supertype
could be more than one of the subtypes
– Indicated with a ‘Gs’
5
Generalization Hierarchy with Overlapping
Subtypes
Chapter 5
Logical Database Design and Normalization of Database
Tables
7
In this chapter, you will learn:
• How to transform ERD into relations• What normalization is and what role it plays
in database design• About the normal forms 1NF, 2NF, 3NF, BCNF,
and 4NF • How normal forms can be transformed from
lower normal forms to higher normal forms• Normalization and E-R modeling are used
concurrently to produce a good database design
• Some situations require denormalization to generate information efficiently
8
Transforming ERD into Relations
• Step one: Map regular entities– Each regular entity type in an ER
diagram is transformed into a relation– The name given to the relation is
generally the same as the entity type– Each simple attribute of the entity
type becomes an attribute of the relation and the identifier of entity becomes the primary key of the corresponding relation
9
Example
Student_ID Student_Name Other_Attributes
STUDENT
10
Transforming ERD into Relations (Cont’d)
• Step two: Map weak entities– Create a new relation and include all
of the simple attributes as the attributes of this relation. Then include the primary key of the identifying relation as a foreign key attribute in this new relation. The primary key of the new relation is the combination of this primary key of the identifying relation and the partial identifier of the weak entity type.
11
Example
EMPLOYEE Has DEPENDENT
Employee_ID Employee_NameDependent_Name
Gender
Date_of_birth
Employee_ID
Employee_Name
EMPLOYEE
DEPENDENT
Dependent_Name
Employee_ID
Date_of_birth
Gender
12
Transforming ERD into Relations (Cont’d)
• Step three: Map binary relationship– Map Binary one-to-many relations
• First create a relation for each of the two entity types participating in the relationship, using the procedure described in step one.
• Next, include the primary key attribute of the entity on the one-side of the relationship as a foreign key in the relation that is on the many-side of the relationship.
13
Example
M
Order_DateOrder_ID
Customer
Customer_NameCustomer_ID
Submits Order
1
(1,1)(0,N)
Customer_ID
Customer_Name
Customer
Order
Order_ID Order_Date
Customer_ID
14
Transforming ERD into Relations (Cont’d)
• Step three: Map binary relationship (Cont’d)– Map binary one-to-one relationships
• First, two relationships are created one for each of the participating entity types.
• Second, the primary key of one of the relations is included as a foreign key in the other relation.
15
Example
LocationCentre_Name
Nurse
Nurse_NameNurse_ID
In_charge Care Centre
1
(1,1)(0,1)
1
Nurse_ID Nurse_NameNurse
Centre_Name
Location Nurse_in_charge
Care Centre
16
Transforming ERD into Relations (Cont’d)
• Step Four: Map composite Entities– First step
• Create three relations: one for each of the two participating entities, and the third for the composite entity. We refer to the relation formed from the composite entity as the composite relation
– Second step• Identifier not assigned: The default primary key
for the composite relation consists of the two primary key attributes from the other two relations.
• Identifier assigned: The primary key for the composite relation is the identifier. The primary keys for the two participating entity types are included as foreign keys in the composite relation.
17
Example
1
Order
Order Line
Order_DateOrder_ID
Quantity
Product Price
Description
Product_ID
(1,N)
M
M
1
(1,1)
(1,1)
(0,N)
18
Example
Order_ID Order_Date
Product_ID
Description
Standard_Price
Product_ID
Order_ID Quantity
Order
Order Line
Product
19
Example
Customer_ID Customer_NameCustomer
Shipment_No
Vendor_ID
Customer_ID
Date
Amount
Shipment
Vendor Vendor_ID
Address
M
AddressVendor_ID
Customer
NameCustomer_ID
Shipment Vendor
Shipment_No Amount
Date
1 M 1
20
Transforming ERD into Relations (Cont’d)
• Step Five: Map unary relationship– Map unary one-to-many relationship
• The entity type in the unary relationship is mapped to a relation using the procedure described in Step one. Then a foreign key attribute is added within the same relation that references the primary key values. A recursive foreign key is a foreign key in a relation that references the primary key values of that same relation.
21
Example
Manages
Employee_ID BirthdateName
Employee
1
M (1,1)
(0,N)
Employee_ID
Name
Birthdate
Manager_ID
Employee
22
Transforming ERD into Relations (Cont’d)
• Step six: Map ternary relationship– Convert a ternary relationship to a
composite entity– To map a composite entity that links
three regular entities, we create a new composite relation. The default primary key of their relation consists of the three primary key attributes for the participating entities. Any attributes of the composite entity become attributes of the new relation
23
Example
1 1
(1,1)
(0,N)
(1,1)(0,N)
(0,N)
(1,1)M
M
1
Treatment
Physician Patient
Physician_ID Physician_NamePatient_ID Patient_Name
DescriptionTreatment_
Code
Patient Treatment
Time
Date
Results
M
24
Example
Patient_ID Patient_Name
Treatment_Code
Description
Physician_ID
Physician_Name
Patient_ID
Physician_ID
Treatment_Code
Date Time Result
Patient
Physician
Treatment
Patient Treatment
25
Transforming ERD into Relations (Cont’d)
• Step seven: Map supertype/subtype relationships1. Create a separate relation for the supertype
and for each of its subtype2. Assign to the relation created for the
supertype the attributes that are common to all members of the supertype, including the primary key
3. Assign to the relation for each subtype the primary key of the supertype, and only those attributes that are unique to that subtype
4. Assign one attribute of the supertype to function as the subtype discriminator
26
Example
Employee_Name
Address
Date_HiredEmployeeEmployee_Number
Employee_Type
SalariedEmployee
HourlyEmployee
Gs
Hourly_Rate Stock_OptionAnnual_Salary
27
Example
Employee_Number
Employee_Name
Address
Employee_Type
Date_Hired
S_Employee_Number
Annual_Salary
Stock_Option
H_Employee_Number
Hourly_Rate
Employee
Hourly_Employee
Salaried_Employee
28
Database Tables and Normalization
• Table is the basic building block in database design
• Normalization is the process for assigning attributes to entities– Reduces data redundancies– Helps eliminate data anomalies– Produces controlled redundancies to link tables
• Normalization stages– 1NF - First normal form– 2NF - Second normal form– 3NF - Third normal form– 4NF - Fourth normal form
29
Need for Normalization
30
Anomalies In the Table
• PRO_NUM intended to be primary key
• Table displays data anomalies– Update
• Modifying JOB_CLASS
– Insertion• New employee must be assigned project
– Deletion• If employee deleted, other vital data lost
31
Conversion to 1NF
• Step 1: Eliminate the Repeating Groups– Present data in a tabular format,
where each cell has a single value and there are no repeating groups
– Eliminate repeating groups by eliminating nulls, making sure that each repeating group attribute contains an appropriate data value
• Step 2: Identify the Primary Key– Primary key must uniquely identify
attribute value
32
Dependency Diagram (1NF)
33
1NF Summarized
• All key attributes defined• No repeating groups in table• All attributes dependent on
primary key• All relational tables satisfy 1NF
requirements
34
Conversion to 2NF
• Start with 1NF form:• Write each key component on
separate line• Write original key on last line• Each component is new table• Write dependent attributes after
each keyPROJECT (PROJ_NUM, PROJ_NAME)EMPLOYEE (EMP_NUM, EMP_NAME, JOB_CLASS, CHG_HOUR)ASSIGN (PROJ_NUM, EMP_NUM, HOURS)
35
2NF Conversion Results
36
2NF Summarized
• In 1NF
• Includes no partial dependencies– No attribute dependent on a portion
of primary key
• Still possible to exhibit transitive dependency– Attributes may be functionally
dependent on nonkey attributes
37
Conversion to 3NF
• Create separate table(s) to eliminate transitive functional dependencies – For every transitive dependency, write its
determinant as a PK for a new table– Identify the Dependent Attributes
PROJECT (PROJ_NUM, PROJ_NAME)ASSIGN (PROJ_NUM, EMP_NUM, HOURS)EMPLOYEE (EMP_NUM, EMP_NAME, JOB_CLASS)JOB (JOB_CLASS, CHG_HOUR)
38
3NF Summarized
• In 2NF
• Contains no transitive dependencies
39
Boyce-Codd Normal Form (BCNF)
• Every determinant in the table is a candidate key– Determinant is an attribute
whose value determines other values within a row
– 3NF table with one candidate key is already in BCNF
40
3NF Table Not in BCNF
41
Decomposition of Table Structure to Meet BCNF
42
Decomposition into BCNF
43
An Example
GRADE( Student_ID, Student_Name, Address, Major, Course_ID, Course_Title, Instructor_Name, Instructor_Office, Grade)
44
Normalization and Database Design
• Normalization should be part of the design process
• E-R Diagram provides macro view• Normalization provides micro view of
entities– Focuses on characteristics of specific entities– May yield additional entities
• Difficult to separate normalization from E-R diagramming
• Business rules must be determined
45
Higher-Level Normal Forms
• Fourth Normal Form (4NF)
– Table is in 3NF
– Has no multiple sets of multivalued dependencies
46
Conversion to 4NF
Stud-ID Course Service
1126 1212F Red Cross
1126 1620F United Way
1126 1320F
Stud-ID Course Service
1126 1212F
1126 1620F
1126 1320F
1126 Red Cross
1126 United Way
Stud-ID Course Service
1126 1212F Red Cross
1126 1620F United Way
1126 1320F
Multivalued Dependencies
Set of Tables in 4NF
Stud-ID Course
1126 1212F
1126 1620F
1126 1320F
Stud-ID Service
1126 Red Cross
1126 United Way
47
Denormalization
• Normalization is one of many database design goals
• Normalized table requires – Additional processing– Loss of system speed
• Normalization purity is difficult to sustain due to conflict in:– Design efficiency– Information requirements– Processing
48
Exercise
Part_No
Description Vendor_Name
Address Unit_Cost
1234 Logic Chips Fast ChipsSmart Chips
Cupertino
Phoenix
10.00
8.00
5678 Memory Chips
Fast Chips
Quality ChipsSmart Chips
Cupertino
Austin
Phoenix
3.00
2.00
5.00
Part Supplier Data
49
Exercise(Cont’d)
• Convert the table to a relation in first normal form (Named Part Supplier)
• List the functional dependency in the Part Supplier and identify a candidate key
• For the relation Part Supplier, identify the followings: an insert anomaly, a delete anomaly, and a modification anomaly.
• Draw a relation schema and show the functional dependencies
• Develop a set of 3NF relations from Part Supplier
50
Chapter 5 Review
• How to transform ERD into relations
• Definitions: 1NF, 2NF, 3NF, BCNF, and 4NF
• How normal forms can be transformed from lower normal forms to higher normal forms