1. Lecture 05: Relational Database Design by ER- & EER-to-Relational Mapping
Dr. Dang Tran Khanh
M.eng. Tran Minh Quang
Department of Information Systems
Faculty of Computer Science & Engineering

2. Outline Main Phases of Database Design Conceptual Database Design
Logical Database Design
ER- & EER-to-Relational Mapping
Exercises
Reading Suggestion:
[1]: Chapters 7, 12
[2]: Chapters 15, 16
Dr. Dang Tran Khanh M.eng. Tran Minh Quang

3. Main Phases of Database Design
Three main phases
Conceptual database design
Logical database design
Physical database design
Detailed discussions: see [1] (chapter 12)
Six phases
Dr. Dang Tran Khanh M.eng. Tran Minh Quang

4. A simplified diagram to illustrate the main phases of database design

5. Main Phases of Database Design
Conceptual database design
The process of constructing a model of the data used in an enterprise, independent of all physical considerations
Logical database design
The process of constructing a model of the data used in an enterprise based on a specific data model (e.g. relational), but independent of a particular DBMS and other physical considerations
Dr. Dang Tran Khanh M.eng. Tran Minh Quang

6. Main Phases of Database Design
Physical database design
The process of producing a description of the implementation of the database on secondary storage; it describes the base relations, file organizations, and indexes design used to achieve efficient access to the data, and any associated integrity constraints and security measures
Dr. Dang Tran Khanh M.eng. Tran Minh Quang

7. Conceptual Database Design Summarization
Read [1]: chapters 3, 12 for details
To build a conceptual data model of the data requirements of the enterprise
Model comprises entity types, relationship types, attributes and attribute domains, primary and alternate keys, structural and integrity constraints
Dr. Dang Tran Khanh M.eng. Tran Minh Quang

8. Conceptual Database Design Summarization
Step 1: Identify entity types
Step 2: Identify relationship types
Step 3: Identify and associate attributes with entity or relationship types
Step 4: Determine attribute domains
Step 5: Determine candidate, primary, and alternate key attributes
Step 6: Consider use of enhanced modeling concepts (optional step)
Step 7: Check model for redundancy
Step 8: Validate conceptual model against user transactions
Step 9: Review conceptual data model with user
Dr. Dang Tran Khanh M.eng. Tran Minh Quang

9. Conceptual Database Design Summarization
Step 1: Identify entity types
To identify the required entity types
Step 2: Identify relationship types
To identify the important relationships that exist between the entity types
Step 3: Identify and associate attributes with entity or relationship types
To associate attributes with the appropriate entity or relationship types and document the details of each attribute
Step 4: Determine attribute domains
To determine domains for the attributes in the data model and document the details of each domain
Dr. Dang Tran Khanh M.eng. Tran Minh Quang

10. Conceptual Database Design Summarization
Step 5: Determine candidate, primary, and alternate key attributes
To identify the candidate key(s) for each entity and if there is more than one candidate key, to choose one to be the primary key and the others as alternate keys
Step 6: Consider use of enhanced modeling concepts (optional step)
To consider the use of enhanced modeling concepts, such as specialization/generalization, categories (union types)
Step 7: Check model for redundancy
To check for the presence of any redundancy in the model and to remove any that does exist
Dr. Dang Tran Khanh M.eng. Tran Minh Quang

11. Conceptual Database Design Summarization
Step 8: Validate conceptual model against user transactions
To ensure that the conceptual model supports the required transactions
Step 9: Review conceptual data model with user
To review the conceptual data model with the user to ensure that the model is a ‘true’ representation of the data requirements of the enterprise
Check with the previous ERD exercises !!
Dr. Dang Tran Khanh M.eng. Tran Minh Quang

12. A simplified diagram to illustrate the main phases of database design

13. Logical Database Design
To translate the conceptual data model into a logical data model and then to validate this model to check that it is structurally correct using normalization and supports the required transactions
Dr. Dang Tran Khanh M.eng. Tran Minh Quang

14. Logical Database Design
Logical database design for the relational model
Step 1: Derive relations for logical data model
Step 2: Validate relations using normalization
Step 3: Validate relations against user transactions
Step 4: Define integrity constraints
Step 5: Review logical data model with user
Step 6: Merge logical data models into global model (optional step)
Step 7: Check for future growth
ER- & EER-to-Relational Mapping
Dr. Dang Tran Khanh M.eng. Tran Minh Quang

15. The ERD for the COMPANY database

16. Result of mapping the COMPANY ER schema into a relational schema

17. ER- & EER-to-Relational Mapping
Step 1: Mapping of Regular Entity Types
Step 2: Mapping of Weak Entity Types
Step 3: Mapping of Binary 1:1 Relationship Types
Step 4: Mapping of Binary 1:N Relationship Types
Step 5: Mapping of Binary M:N Relationship Types
Step 6: Mapping of Multivalued attributes
Step 7: Mapping of N-ary Relationship Types
EER-
Step 8: Options for Mapping Specialization or Generalization.
Step 9: Mapping of Union Types (Categories)
Dr. Dang Tran Khanh M.eng. Tran Minh Quang

18. ER-to-Relational Mapping
Step 1: Mapping of Regular (strong) Entity Types
Entity --> Relation
Attribute of entity --> Attribute of relation
Primary key of entity --> Primary key of relation
Example: We create the relations EMPLOYEE, DEPARTMENT, and PROJECT in the relational schema corresponding to the regular entities in the ER diagram. SSN, DNUMBER, and PNUMBER are the primary keys for the relations EMPLOYEE, DEPARTMENT, and PROJECT as shown
Dr. Dang Tran Khanh M.eng. Tran Minh Quang

19. The ERD for the COMPANY database
Strong Entity Types

20. ER-to-Relational Mapping
Step 2: Mapping of Weak Entity Types
For each weak entity type W in the ER schema with owner entity type E, create a relation R and include all simple attributes (or simple components of composite attributes) of W as attributes of R
In addition, include as foreign key attributes of R the primary key attribute(s) of the relation(s) that correspond to the owner entity type(s)
The primary key of R is the combination of the primary key(s) of the owner(s) and the partial key of the weak entity type W, if any
Example: Create the relation DEPENDENT in this step to correspond to the weak entity type DEPENDENT. Include the primary key SSN of the EMPLOYEE relation as a foreign key attribute of DEPENDENT (renamed to ESSN)
The primary key of the DEPENDENT relation is the combination {ESSN, DEPENDENT_NAME} because DEPENDENT_NAME is the partial key of DEPENDENT
Note: CASCADE option as implemented
Dr. Dang Tran Khanh M.eng. Tran Minh Quang

21. The ERD for the COMPANY database
Owner’s PK PK
Weak Entity Types
Partial key

22. Result of mapping the COMPANY ER schema into a relational schema

23. ER-to-Relational Mapping
Step 1: Mapping of Regular Entity Types
Step 2: Mapping of Weak Entity Types
Step 3: Mapping of Binary 1:1 Relationship Types
Step 4: Mapping of Binary 1:N Relationship Types
Step 5: Mapping of Binary M:N Relationship Types
Step 6: Mapping of Multivalued attributes
Step 7: Mapping of N-ary Relationship Types
Transformation of binary relationships - depends on functionality of relationship and membership class of participating entity types
Dr. Dang Tran Khanh M.eng. Tran Minh Quang

24. ER-to-Relational Mapping
Mandatory membership class
For two entity types E1 and E2: If E2 is a mandatory member of an N:1 (or 1:1) relationship with E1, then the relation for E2 will include the prime attributes of E1 as a foreign key to represent the relationship
For a 1:1 relationship: If the membership class for E1 and E2 are both mandatory, a foreign key can be used in either relation
For an N:1 relationship: If the membership class of E2, which is at the N-side of the relationship, is optional (i.e. partial), then the above guideline is not applicable
Dr. Dang Tran Khanh M.eng. Tran Minh Quang

25. ER-to-Relational Mapping
Assume every module must be offered by a department, then the entity type MODULE is a mandatory member of the relationship OFFER. The relation for MODULE is:
MODULE(MDL-NUMBER, TITLE, TERM, ..., DNAME)
MODULE
DEPARTMENT
OFFER 1 N
Dr. Dang Tran Khanh M.eng. Tran Minh Quang

26. The ERD for the COMPANY database
N:1 Relationships

27. Result of mapping the COMPANY ER schema into a relational schema

28. ER-to-Relational Mapping
Optional membership classes
If entity type E2 is an optional member of the N:1 relationship with entity type E1 (i.e. E2 is at the N-side of the relationship), then the relationship is usually represented by a new relation containing the prime attributes of E1 and E2, together with any attributes of the relationship. The key of the entity type at the N-side (i.e. E2) will become the key of the new relation
If both entity types in a 1:1 relationship have the optional membership, a new relation is created which contains the prime attributes of both entity types, together with any attributes of the relationship. The prime attribute(s) of either entity type will be the key of the new relation
Dr. Dang Tran Khanh M.eng. Tran Minh Quang

29. ER-to-Relational Mapping
One possible representation of the relationship:
BORROWER(BNUMBER, NAME, ADDRESS, ...)
BOOK(ISBN, TITLE, ..., BNUMBER)
A better alternative:
BOOK(ISBN, TITLE, ...)
ON_LOAN(ISBN, BNUMBER)
Dr. Dang Tran Khanh M.eng. Tran Minh Quang

30. The ERD for the COMPANY database
1:N (both optional)

31. Result of mapping the COMPANY ER schema into a relational schema
???
[1]: Step 4, p. 195, chapter 7

32. ER-to-Relational Mapping
N:M binary relationships:
An N:M relationship is always represented by a new relation which consists of the prime attributes of both participating entity types together with any attributes of the relationship
The combination of the prime attributes will form the primary key of the new relation
Example: ENROL is an M:N relationship between STUDENT and MODULE. To represent the relationship, we have a new relation:
ENROL(SNUMBER, MDL-NUMBER, DATE)
Dr. Dang Tran Khanh M.eng. Tran Minh Quang

33. The ERD for the COMPANY database
M:N

34. Result of mapping the COMPANY ER schema into a relational schema

35. ER-to-Relational Mapping
Step 1: Mapping of Regular Entity Types
Step 2: Mapping of Weak Entity Types
Step 3: Mapping of Binary 1:1 Relationship Types
Step 4: Mapping of Binary 1:N Relationship Types
Step 5: Mapping of Binary M:N Relationship Types
Step 6: Mapping of Multivalued attributes
Step 7: Mapping of N-ary Relationship Types
Dr. Dang Tran Khanh M.eng. Tran Minh Quang

36. ER-to-Relational Mapping
Transformation of recursive/involuted relationships
Relationship among different instances of the same entity
The name(s) of the prime attribute(s) needs to be changed to reflect the role each entity plays in the relationship

37. ER-to-Relational Mapping
Example 1: 1:1 involuted relationship, in which the memberships for both entities are optional
PERSON(ID, NAME, ADDRESS, ...)
MARRY(HUSBAND-ID, WIFE_ID, DATE_OF_MARRIAGE)
Dr. Dang Tran Khanh M.eng. Tran Minh Quang

38. ER-to-Relational Mapping
Example 2: 1:M involuted relationship.
If the relationship is mandatory or almost mandatory:
EMPLOYEE(ID, ENAME, ..., SUPERVISOR_ID)
If the relationship is optional:
EMPLOYEE(ID, ENAME, ...)
SUPERVISE(ID, START_DATE, ..., SUPERVISOR_ID)
Example 3: N:M involuted relationship
PART(PNUMBER, DESCRIPTION, ...)
COMPRISE( MAJOR-PNUMBER, MINOR-PNUMBER, QUANTITY)
Dr. Dang Tran Khanh M.eng. Tran Minh Quang

39. ER- & EER-to-Relational Mapping
Step 1: Mapping of Regular Entity Types
Step 2: Mapping of Weak Entity Types
Step 3: Mapping of Binary 1:1 Relationship Types
Step 4: Mapping of Binary 1:N Relationship Types
Step 5: Mapping of Binary M:N Relationship Types
Step 6: Mapping of Multivalued attributes
Step 7: Mapping of N-ary Relationship Types
EER-
Step 8: Options for Mapping Specialization or Generalization.
Step 9: Mapping of Union Types (Categories)
Dr. Dang Tran Khanh M.eng. Tran Minh Quang

40. ER-to-Relational Mapping
Step 6: Mapping of Multivalued attributes
For each multivalued attribute A, create a new relation R. This relation R will include an attribute corresponding to A, plus the primary key attribute K-as a foreign key in R-of the relation that represents the entity type or relationship type that has A as an attribute
The primary key of R is the combination of A and K. If the multivalued attribute is composite, we include its simple components
Example: The relation DEPT_LOCATIONS is created. The attribute DLOCATION represents the multivalued attribute LOCATIONS of DEPARTMENT, while DNUMBER-as foreign key-represents the primary key of the DEPARTMENT relation. The primary key of R is the combination of {DNUMBER, DLOCATION}
Dr. Dang Tran Khanh M.eng. Tran Minh Quang

41. The ERD for the COMPANY database
Multivalued Attr.

42. Result of mapping the COMPANY ER schema into a relational schema

43. ER-to-Relational Mapping
Step 7: Mapping of N-ary Relationship Types
For each n-ary relationship type R, where n>2, create a new relationship S to represent R
Include as foreign key attributes in S the primary keys of the relations that represent the participating entity types
Also include any simple attributes of the n-ary relationship type (or simple components of composite attributes) as attributes of S
Example: The relationship type SUPPY in the ER below. This can be mapped to the relation SUPPLY shown in the relational schema, whose primary key is the combination of the three foreign keys {SNAME, PARTNO, PROJNAME}
Dr. Dang Tran Khanh M.eng. Tran Minh Quang

44. ER-to-Relational Mapping FIGURE 4
ER-to-Relational Mapping FIGURE 4.11 Ternary relationship types (a) The SUPPLY relationship
Note: if the cardinality constraint on any of the entity types E participating in the relationship is 1, the PK should not include the FK attributes that reference the relation E’ corresponding to E (see section 4.7 [1])

45. ER-to-Relational Mapping Summary of Mapping Constructs & Constraints
Correspondence between ER and Relational Models
ER Model Relational Model
Entity type “Entity” relation
1:1 or 1:N relationship type Foreign key (or “relationship” relation)
M:N relationship type “Relationship” relation and two foreign keys
n-ary relationship type “Relationship” relation and n foreign keys
Simple attribute Attribute
Composite attribute Set of simple component attributes
Multivalued attribute Relation and foreign key
Value set Domain
Key attribute Primary (or secondary) key
Dr. Dang Tran Khanh M.eng. Tran Minh Quang

46. ER- & EER-to-Relational Mapping
Step 1: Mapping of Regular Entity Types
Step 2: Mapping of Weak Entity Types
Step 3: Mapping of Binary 1:1 Relationship Types
Step 4: Mapping of Binary 1:N Relationship Types
Step 5: Mapping of Binary M:N Relationship Types
Step 6: Mapping of Multivalued attributes
Step 7: Mapping of N-ary Relationship Types
EER-
Step 8: Options for Mapping Specialization or Generalization.
Step 9: Mapping of Union Types (Categories)
Dr. Dang Tran Khanh M.eng. Tran Minh Quang

47. EER-to-Relational Mapping
Step8: Options for Mapping Specialization or Generalization.
Convert each specialization with m subclasses {S1, S2,….,Sm} and generalized superclass C, where the attributes of C are {k,a1,…an} and k is the (primary) key, into relational schemas using one of the four following options:
Option 8A: Multiple relations-Superclass and subclasses.
Create a relation L for C with attributes Attrs(L) = {k,a1,…an} and PK(L) = k. Create a relation Li for each subclass Si, 1 <= i <= m, with the attributesAttrs(Li) = {k} U {attributes of Si} and PK(Li)=k. This option works for any specialization (total or partial, disjoint of over-lapping).
Option 8B: Multiple relations-Subclass relations only
Create a relation Li for each subclass Si, 1 <= i <= m, with the attributes Attr(Li) = {attributes of Si} U {k,a1…,an} and PK(Li) = k. This option only works for a specialization whose subclasses are total (every entity in the superclass must belong to (at least) one of the subclasses)
Dr. Dang Tran Khanh M.eng. Tran Minh Quang

48. EER-to-Relational Mapping
Option 8C: Single relation with one type attribute
Create a single relation L with attributes Attrs(L) = {k,a1,…an} U {attributes of S1} U…U {attributes of Sm} U {t} and PK(L) = k. The attribute t is called a type (or discriminating) attribute that indicates the subclass to which each tuple belongs
Option 8D: Single relation with multiple type attributes
Create a single relation schema L with attributes Attrs(L) = {k,a1,…an} U {attributes of S1} U…U {attributes of Sm} U {t1, t2,…,tm} and PK(L) = k. Each ti, 1 <= i <= m, is a Boolean type attribute indicating whether a tuple belongs to the subclass Si
Option 8A is preferred !!
Dr. Dang Tran Khanh M.eng. Tran Minh Quang

49. Example: Option 8A

50. Example: Option 8B
Tonnage

51. Serving as the type attribute
Example: Option 8C
EngType
Serving as the type attribute

52. Boolean type attributes
Example: Option 8D
Boolean type attributes

53. EER-to-Relational Mapping
Mapping of Shared Subclasses (Multiple Inheritance)
A shared subclass, such as STUDENT_ASSISTANT, is a subclass of several classes, indicating multiple inheritance. These classes must all have the same key attribute; otherwise, the shared subclass would be modeled as a category.
We can apply any of the options discussed in Step 8 to a shared subclass, subject to the restriction discussed in Step 8 of the mapping algorithm. Below both 8C and 8D are used for the shared class STUDENT_ASSISTANT
Dr. Dang Tran Khanh M.eng. Tran Minh Quang

54. Example: Mapping of Shared Subclasses

55. Example: Mapping of Shared Subclasses
Major
Course

56. EER-to-Relational Mapping
Step 9: Mapping of Union Types (Categories).
For mapping a category whose defining superclasses have different keys, it is customary to specify a new key attribute, called a surrogate key, when creating a relation to correspond to the category.
In the example below we can create a relation OWNER to correspond to the OWNER category and include any attributes of the category in this relation. The primary key of the OWNER relation is the surrogate key, which we called OwnerId
We also include the surrogate key attribute OwnerId as FK in each relation corresponding to a superclass of the category in order to specify the correspondence in values between the surrogate key and the PK of each superclass
Dr. Dang Tran Khanh M.eng. Tran Minh Quang

57. Example
OwnerId
CYear

58. Exercises (in-class) Map the above ERD into relational schemas.
Justify your choice of mapping options.

59. Summary 3 Main Phases of Database Design: An Overview
Conceptual Database Design: A Summarization
Logical Database Design
ER- & EER-to-Relational Mapping
Exercises & homework
Reading Suggestion & homework: do not forget !!
Next Lecture: (students’ presentation)
Relational Algebra & Relational Calculus
[1]: Chapter 6
Dr. Dang Tran Khanh M.eng. Tran Minh Quang

60. Exercises Homework: [1]: Exercise 7.5, p. 204
Map all ERDs of the previous exercises to corresponding relational database schemas
Dr. Dang Tran Khanh M.eng. Tran Minh Quang

61. Exercises Give a database scheme of a company as Homework:
customer(C-Id, name, addr, city)
product(P-Id, name, unit, description)
buying(C-id, P-id, date, quantity, price)
selling(C-id, P-id, date, quantity, price)
Answer following questions using SQL
Dr. Dang Tran Khanh M.eng. Tran Minh Quang

62. Exercises Homework: Display all customers
Display all customers but the information to be displayed are customer id and customer name only
Similar to question 2 but customers to be selected are in HCM city only
Display all the products sold on 10/03/2007
Display all the customers who supplied product P01 on 10/03/2007
Similar to question 5 but the information to be displayed includes C-id, C-name, P-id, P-name.
Dr. Dang Tran Khanh M.eng. Tran Minh Quang

63. Exercises
Homework:
7. Display customers who buy the products supplied by customer whose name is “Intel”
8. Display product which are concurrently bought and sold on 10/03/2007
9. Display customers who paid the greatest amount of money for buying product on 10/03/2007
10. Display customers who got the greatest amount of money by selling product to the company in the year 2006
Dr. Dang Tran Khanh M.eng. Tran Minh Quang

64. Q&A
Questions ??
Dr. Dang Tran Khanh M.eng. Tran Minh Quang