1. Database Management Systems
Dr. Mohamed Khafagy

2. Overview of Database Design Process
Two main activities:
Database design
Applications design
To design the conceptual schema for a database application
Applications design focuses on the programs and interfaces that access the database

3. Overview of Database Design Process
draw the entity
Relationship diagram
converting the entity relationship
diagram into tables
executing the tables in an actual DBMS software file

4. Example COMPANY Database
We need to create a database schema design based on the following (simplified) requirements of the COMPANY Database:
The company is organized into DEPARTMENTs. Each department has a name, number and an employee who manages the department. We keep track of the start date of the department manager. A department may have several locations.
Each department controls a number of PROJECTs. Each project has a unique name, unique number and is located at a single location.

5. Example COMPANY Database (Contd.)
We store each EMPLOYEE’s social security number, address, salary, sex, and birthdate.
Each employee works for one department but may work on several projects.
We keep track of the number of hours per week that an employee currently works on each project.
We also keep track of the direct supervisor of each employee.
Each employee may have a number of DEPENDENTs.
For each dependent, we keep track of their name, sex, birthdate, and relationship to the employee.

6. ER Model Concepts Entities and Attributes
Entities are specific objects or things in the mini-world that are represented in the database.
For example the EMPLOYEE John Smith, the Research DEPARTMENT, the ProductX PROJECT
Attributes are properties used to describe an entity.
For example an EMPLOYEE entity may have the attributes Name, SSN, Address, Sex, BirthDate
A specific entity will have a value for each of its attributes.
For example a specific employee entity may have Name='John Smith', SSN=' ', Address ='731, Fondren, Houston, TX', Sex='M', BirthDate='09-JAN-55‘
Each attribute has a value set (or data type) associated with it – e.g. integer, string, subrange, enumerated type, …

7. Types of Attributes (1) Simple Composite Multi-valued
Each entity has a single atomic value for the attribute. For example, SSN or Sex.
Composite
The attribute may be composed of several components. For example:
Address(Apt#, House#, Street, City, State, ZipCode, Country), or
Name(FirstName, MiddleName, LastName).
Composition may form a hierarchy where some components are themselves composite.
Multi-valued
An entity may have multiple values for that attribute. For example, Color of a CAR or PreviousDegrees of a STUDENT.
Denoted as {Color} or {PreviousDegrees}.

8. Types of Attributes (2)
In general, composite and multi-valued attributes may be nested arbitrarily to any number of levels, although this is rare.
For example, PreviousDegrees of a STUDENT is a composite multi-valued attribute denoted by {PreviousDegrees (College, Year, Degree, Field)}
Multiple PreviousDegrees values can exist, each has four subcomponent attributes:
College, Year, Degree, Field

9. Example of a composite attribute

10. Entity Types and Key Attributes (1)
Entities with the same basic attributes are grouped or typed into an entity type.
For example, the entity type EMPLOYEE and PROJECT.
An attribute of an entity type for which each entity must have a unique value is called a key attribute of the entity type.
For example, SSN of EMPLOYEE.

11. Entity Types and Key Attributes (2)
A key attribute may be composite.
VehicleTagNumber is a key of the CAR entity type with components (Number, State).
An entity type may have more than one key.
The CAR entity type may have two keys:
VehicleIdentificationNumber (popularly called VIN)
VehicleTagNumber (Number, State), aka license plate number.
Each key is underlined

12. Keys
Let K  R
K is a superkey of R if values for K are sufficient to identify a unique tuple of each possible relation r(R)
by “possible r ” we mean a relation r that could exist in the enterprise we are modeling.
Example: {customer_name, customer_street} and {customer_name} are both superkeys of Customer, if no two customers can possibly have the same name
In real life, an attribute such as customer_id would be used instead of customer_name to uniquely identify customers, but we omit it to keep our examples small, and instead assume customer names are unique.

13. Keys (Cont.)
K is a candidate key if K is minimal Example: {customer_name} is a candidate key for Customer, since it is a superkey and no subset of it is a superkey.
Primary key: a candidate key chosen as the principal means of identifying tuples within a relation
Should choose an attribute whose value never, or very rarely, changes.
E.g. address is unique, but may change

14. Foreign Keys
A relation schema may have an attribute that corresponds to the primary key of another relation. The attribute is called a foreign key.
E.g. customer_name and account_number attributes of depositor are foreign keys to customer and account respectively.
Only values occurring in the primary key attribute of the referenced relation may occur in the foreign key attribute of the referencing relation.
Schema diagram

15. Displaying an Entity type
In ER diagrams, an entity type is displayed in a rectangular box
Attributes are displayed in ovals
Each attribute is connected to its entity type
Components of a composite attribute are connected to the oval representing the composite attribute
Each key attribute is underlined
Multivalued attributes displayed in double ovals
See CAR example on next slide

16. Entity Type CAR with two keys and a corresponding Entity Set

17. Initial Design of Entity Types for the COMPANY Database Schema
Based on the requirements, we can identify four initial entity types in the COMPANY database:
DEPARTMENT
PROJECT
EMPLOYEE
DEPENDENT
Their initial design is shown on the following slide
The initial attributes shown are derived from the requirements description

18. Initial Design of Entity Types: EMPLOYEE, DEPARTMENT, PROJECT, DEPENDENT

19. Refining the initial design by introducing relationships
The initial design is typically not complete
Some aspects in the requirements will be represented as relationships
ER model has three main concepts:
Entities (and their entity types and entity sets)
Attributes (simple, composite, multivalued)
Relationships (and their relationship types and relationship sets)
We introduce relationship concepts next

20. Relationships and Relationship Types (1)
A relationship relates two or more distinct entities with a specific meaning.
For example, EMPLOYEE John Smith works on the ProductX PROJECT, or EMPLOYEE Franklin Wong manages the Research DEPARTMENT.
Relationships of the same type are grouped or typed into a relationship type.
For example, the WORKS_ON relationship type in which EMPLOYEEs and PROJECTs participate, or the MANAGES relationship type in which EMPLOYEEs and DEPARTMENTs participate.
The degree of a relationship type is the number of participating entity types.
Both MANAGES and WORKS_ON are binary relationships.

21. Relationship instances of the WORKS_FOR N:1 relationship between EMPLOYEE and DEPARTMENT

22. Relationship instances of the M:N WORKS_ON relationship between EMPLOYEE and PROJECT

23. Relationship type vs. relationship set (1)
Is the schema description of a relationship
Identifies the relationship name and the participating entity types
Also identifies certain relationship constraints
Relationship Set:
The current set of relationship instances represented in the database
The current state of a relationship type

24. Relationship type vs. relationship set (2)
Previous figures displayed the relationship sets
Each instance in the set relates individual participating entities – one from each participating entity type
In ER diagrams, we represent the relationship type as follows:
Diamond-shaped box is used to display a relationship type
Connected to the participating entity types via straight lines

25. Refining the COMPANY database schema by introducing relationships
By examining the requirements, six relationship types are identified
All are binary relationships( degree 2)
Listed below with their participating entity types:
WORKS_FOR (between EMPLOYEE, DEPARTMENT)
MANAGES (also between EMPLOYEE, DEPARTMENT)
CONTROLS (between DEPARTMENT, PROJECT)
WORKS_ON (between EMPLOYEE, PROJECT)
SUPERVISION (between EMPLOYEE (as subordinate), EMPLOYEE (as supervisor))
DEPENDENTS_OF (between EMPLOYEE, DEPENDENT)

26. ER DIAGRAM – Relationship Types are: WORKS_FOR, MANAGES, WORKS_ON, CONTROLS, SUPERVISION, DEPENDENTS_OF

27. Recursive Relationship Type
A relationship type with the same participating entity type in distinct roles
Example: the SUPERVISION relationship
EMPLOYEE participates twice in two distinct roles:
supervisor (or boss) role
supervisee (or subordinate) role
Each relationship instance relates two distinct EMPLOYEE entities:
One employee in supervisor role
One employee in supervisee role

28. Weak Entity Types An entity that does not have a key attribute
A weak entity must participate in an identifying relationship type with an owner or identifying entity type
Entities are identified by the combination of:
A partial key of the weak entity type
The particular entity they are related to in the identifying entity type
Example:
A DEPENDENT entity is identified by the dependent’s first name, and the specific EMPLOYEE with whom the dependent is related
Name of DEPENDENT is the partial key
DEPENDENT is a weak entity type
EMPLOYEE is its identifying entity type via the identifying relationship type DEPENDENT_OF

29. Many-to-one (N:1) Relationship

30. Many-to-many (M:N) Relationship

31. Displaying a recursive relationship
In a recursive relationship type.
Both participations are same entity type in different roles.
For example, SUPERVISION relationships between EMPLOYEE (in role of supervisor or boss) and (another) EMPLOYEE (in role of subordinate or worker).
In following figure, first role participation labeled with 1 and second role participation labeled with 2.
In ER diagram, need to display role names to distinguish participations.

32. A Recursive Relationship Supervision`

33. Recursive Relationship Type is: SUPERVISION (participation role names are shown)

34. Attributes of Relationship types
A relationship type can have attributes:
For example, HoursPerWeek of WORKS_ON
Its value for each relationship instance describes the number of hours per week that an EMPLOYEE works on a PROJECT.
A value of HoursPerWeek depends on a particular (employee, project) combination
Most relationship attributes are used with M:N relationships
In 1:N relationships, they can be transferred to the entity type on the N-side of the relationship

35. Example Attribute of a Relationship Type: Hours of WORKS_ON

36. Alternative (min, max) notation for relationship structural constraints:
Specified on each participation of an entity type E in a relationship type R
Specifies that each entity e in E participates in at least min and at most max relationship instances in R
Default(no constraint): min=0, max=n (signifying no limit)
Must have minmax, min0, max 1
Derived from the knowledge of mini-world constraints
Examples:
A department has exactly one manager and an employee can manage at most one department.
Specify (0,1) for participation of EMPLOYEE in MANAGES
Specify (1,1) for participation of DEPARTMENT in MANAGES
An employee can work for exactly one department but a department can have any number of employees.
Specify (1,1) for participation of EMPLOYEE in WORKS_FOR
Specify (0,n) for participation of DEPARTMENT in WORKS_FOR
Database Systems
Data Models

37. The (min,max) notation for relationship constraints
Read the min,max numbers next to the entity type and looking away from the entity type

38. COMPANY ER Schema Diagram using (min, max) notation

39. Subclasses and Superclasses (1)
An entity type may have additional meaningful subgroupings of its entities
Example: EMPLOYEE may be further grouped into:
SECRETARY, ENGINEER, TECHNICIAN, …
Based on the EMPLOYEE’s Job
MANAGER
EMPLOYEEs who are managers
SALARIED_EMPLOYEE, HOURLY_EMPLOYEE
Based on the EMPLOYEE’s method of pay
EER diagrams extend ER diagrams to represent these additional subgroupings, called subclasses or subtypes
Database Systems
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40. Subclasses and Superclasses
Database Systems
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41. Subclasses and Superclasses (2)
Each of these subgroupings is a subset of EMPLOYEE entities
Each is called a subclass of EMPLOYEE
EMPLOYEE is the superclass for each of these subclasses
These are called superclass/subclass relationships:
EMPLOYEE/SECRETARY
EMPLOYEE/TECHNICIAN
EMPLOYEE/MANAGER …
Database Systems
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42. Subclasses and Superclasses (3)
These are also called IS-A relationships
SECRETARY IS-A EMPLOYEE, TECHNICIAN IS-A EMPLOYEE, ….
Note: An entity that is member of a subclass represents the same real-world entity as some member of the superclass:
The subclass member is the same entity in a distinct specific role
An entity cannot exist in the database merely by being a member of a subclass; it must also be a member of the superclass
A member of the superclass can be optionally included as a member of any number of its subclasses
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43. Subclasses and Superclasses (4)
Examples:
A salaried employee who is also an engineer belongs to the two subclasses:
ENGINEER, and
SALARIED_EMPLOYEE
A salaried employee who is also an engineering manager belongs to the three subclasses:
MANAGER,
It is not necessary that every entity in a superclass be a member of some subclass
Database Systems
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44. Representing Specialization in EER Diagrams
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45. Attribute Inheritance in Superclass / Subclass Relationships
An entity that is member of a subclass inherits
All attributes of the entity as a member of the superclass
All relationships of the entity as a member of the superclass
Example:
In the previous slide, SECRETARY (as well as TECHNICIAN and ENGINEER) inherit the attributes Name, SSN, …, from EMPLOYEE
Every SECRETARY entity will have values for the inherited attributes
Database Systems
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46. Specialization (1)
Specialization is the process of defining a set of subclasses of a superclass
The set of subclasses is based upon some distinguishing characteristics of the entities in the superclass
Example: {SECRETARY, ENGINEER, TECHNICIAN} is a specialization of EMPLOYEE based upon job type.
May have several specializations of the same superclass
Database Systems
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47. Specialization (2)
Example: Another specialization of EMPLOYEE based on method of pay is {SALARIED_EMPLOYEE, HOURLY_EMPLOYEE}.
Superclass/subclass relationships and specialization can be diagrammatically represented in EER diagrams
Attributes of a subclass are called specific or local attributes.
For example, the attribute TypingSpeed of SECRETARY
The subclass can also participate in specific relationship types.
For example, a relationship BELONGS_TO of HOURLY_EMPLOYEE
Database Systems
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48. Specialization (3)
Database Systems
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49. Generalization
Generalization is the reverse of the specialization process
Several classes with common features are generalized into a superclass;
original classes become its subclasses
Example: CAR, TRUCK generalized into VEHICLE;
both CAR, TRUCK become subclasses of the superclass VEHICLE.
We can view {CAR, TRUCK} as a specialization of VEHICLE
Alternatively, we can view VEHICLE as a generalization of CAR and TRUCK
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50. Generalization (2)
Database Systems
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51. Generalization and Specialization (1)
Diagrammatic notation are sometimes used to distinguish between generalization and specialization
Arrow pointing to the generalized superclass represents a generalization
Arrows pointing to the specialized subclasses represent a specialization
We do not use this notation because it is often subjective as to which process is more appropriate for a particular situation
We advocate not drawing any arrows
Database Systems
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52. Generalization and Specialization (2)
Data Modeling with Specialization and Generalization
A superclass or subclass represents a collection (or set or grouping) of entities
It also represents a particular type of entity
Shown in rectangles in EER diagrams (as are entity types)
We can call all entity types (and their corresponding collections) classes, whether they are entity types, superclasses, or subclasses
Database Systems
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53. Constraints on Specialization and Generalization (1)
If we can determine exactly those entities that will become members of each subclass by a condition, the subclasses are called predicate-defined (or condition- defined) subclasses
Condition is a constraint that determines subclass members
Display a predicate-defined subclass by writing the predicate condition next to the line attaching the subclass to its superclass
Database Systems
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54. Constraints on Specialization and Generalization (2)
If all subclasses in a specialization have membership condition on same attribute of the superclass, specialization is called an attribute-defined specialization
Attribute is called the defining attribute of the specialization
Example: JobType is the defining attribute of the specialization {SECRETARY, TECHNICIAN, ENGINEER} of EMPLOYEE
If no condition determines membership, the subclass is called user- defined
Membership in a subclass is determined by the database users by applying an operation to add an entity to the subclass
Membership in the subclass is specified individually for each entity in the superclass by the user
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55. Displaying an attribute-defined specialization in EER diagrams
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56. Constraints on Specialization/Generalization
Specialization may consists of multiple subclasses (circle notation) or a single subclass (no circle notation).
Disjointness Constraint.
Entity must be a member of at most one of the subclasses. It uses (d) notation.
Overlap Constraint.
Entity may be a member of more than one subclass. It uses (o) notation.
Total Specialization.
Every entity in the superclass MUST be a member of some subclass. It uses double line notation.
Partial Specialization.
Entity does not have to belong to any of the subclasses. Employee does not belong to secretary, engineer, technician.
Database Systems
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57. Specialization/Generalization Constraints Types
Hence, we have four types of specialization/generalization:
Disjoint, total
Disjoint, partial
Overlapping, total
Overlapping, partial
Note: Generalization usually is total because the superclass is derived from the subclasses.
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58. Example of disjoint partial Specialization
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59. Example of overlapping total Specialization
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60. Specialization/Generalization Hierarchies and Lattices
Specialization Hierarchy.
A subclass participates as a subclass in only one class/subclass relationship.
Specialization Lattice.
A subclass can be a subclass in more than one class/subclass relationship.
Leaf Node.
Class that has no subclass of its own.
Shared Subclass.
Subclass with more than one superclass (Figure next slide).
Multiple Inheritance
Entity inherits attributes and relationships from multiple classes.
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61. Shared Subclass “Engineering_Manager”
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62. Utilizing Specialization and Generalization in Conceptual Data Modeling
A top down conceptual refinement process
In specialization, start with an entity type and then define subclasses of the entity type by successive specialization
A bottom up conceptual synthesis process
In generalization, start with many entity types and generalize those that have common properties
In practice, a combination of both processes is usually employed
Database Systems
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63. Specialization / Generalization Lattice Example (UNIVERSITY)
Database Systems
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64. Categories (UNION TYPES) (1)
All of the superclass/subclass relationships we have seen thus far have a single superclass
A shared subclass is a subclass in:
more than one distinct superclass/subclass relationships
each relationships has a single superclass
shared subclass leads to multiple inheritance
In some cases, we need to model a single superclass/subclass relationship with more than one superclass
Superclasses can represent different entity types
Such a subclass is called a category or UNION TYPE
Database Systems
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65. Categories (UNION TYPES) (2)
Example: In a database for vehicle registration, a vehicle owner can be a PERSON, a BANK (holding a lien on a vehicle) or a COMPANY.
A category (UNION type) called OWNER is created to represent a subset of the union of the three superclasses COMPANY, BANK, and PERSON
A category member must exist in at least one of its superclasses
Difference from shared subclass, which is a:
subset of the intersection of its superclasses
shared subclass member must exist in all of its superclasses
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66. Two categories (UNION types): OWNER, REGISTERED_VEHICLE
Database Systems
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67. Alternative diagrammatic notations
ER/EER diagrams are a specific notation for displaying the concepts of the model diagrammatically
DB design tools use many alternative notations for the same or similar concepts
One popular alternative notation uses UML class diagrams
see next slides for UML class diagrams and other alternative notations
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68. UML Example for Displaying Specialization / Generalization
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69. Conceptual Object Modeling Using UML Class Diagrams
EER
UML
Entity
Class
Week Entity
Qualified association/Qualified aggregation)
Composite attribute
Structured domain
Multivalue attribute
Separate class
Relationship
Associations
(min, max)
Multiplicities
Database Systems
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70. Alternative Diagrammatic Notations
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71. Relational Database Domain
Integrity Constraints : ( PK, UK, NN, FK, Check)
Data types

72. ER-to-Relational Mapping Tables
Step 1: Mapping of Regular Entity Types
Step 2: Mapping of Weak Entity Types
Step 3: Mapping of Binary 1:1 Relation Types
Step 4: Mapping of Binary 1:N Relationship Types.
Step 5: Mapping of Binary M:N Relationship Types.
Step 6: Mapping of Multi-valued attributes.
Step 7: Mapping of N-ary Relationship Types.

73. Step 1: Mapping of Regular Entity Types
Create table for each entity type
Choose one of key attributes to be the primary key

74. Step 2: Mapping of Weak Entity Types
Create table for each weak entity.
Add foreign key that correspond to the owner entity type.
Choose the primary key : ( FK + weak entity Partial PK if any)

75. Step 3: Mapping of Binary 1:1 Relation Types
Merged two tables if both sides are Mandatory.
Add FK into table with the total participation relationship to represent optional side.
Create third table if both sides are optional.

76. Step 4: Mapping of Binary 1:N Relationship Types.
Add FK to N-side table
Add any simple attributes of relationship as column to N-side table.

77. Step 5: Mapping of Binary M:N Relationship Types.
Create a new third table
Add FKs to the new table for both parent tables
Add simple attributes of relationship to the new table if any .

78. Step 6: Mapping of Multi-valued attributes.
Create new table for each multi-valued attribute
Table will include two columns.
one for multi-valued attribute + FK column.

79. Step 7: Mapping of N-ary Relationship Types.
If n > 2 then :
Create a new third table
Add FKs to the new table for all parent tables
Add simple attributes of relationship to the new table if any .

81. Mapping Result

82. ERD Case Study
An organization makes many models of cars, where a model is characterized by a unique name and a suffix (such as GL or XL) and an engine size.
Each model is made up from many parts and Each part has a description , an id code, production year, and many images.
each part may be used in the manufacturing of more than one model

83. ERD Case Study
Each model must be produced at just one of the firm's factories, which are located in London, Birmingham, Bristol, Wolverhampton and Manchester - one in each city. Each factory has number of machines, capacity, and computer system used ( OS , DBMS, Internet).
A factory produces many models of cars and many types of parts. Although the parts and model produced in the same factory.
although each type of part is produced at one factory only and the model is produced in the same factory.
Discuss Ternary relationship.

84. Ternary Relationship

85. ERD Case Study 2
A country bus company owns a number of buses. A bus is characterized by number, No. of Chairs, Options ( AC , Automatic, PS) , and brand-name
Each bus is allocated to a particular route, although some routes may have several buses . Each route is described by KM, start point, end point and the duration.

86. ERD Case Study 2 Each route can passes through a number of towns.
A town may be situated along several routes. We keep track of unique name and station name in each town.
One or more drivers are allocated to one route during a period of time. The system keep information about the driver name , mobile number , hire date, basic salary , job grade.
The system keep information about any changes in the allocations of the drivers to the routes and the last route assigned to each driver.
Oute

87. ERD Narrative
A database for a banking system is used to control withdrawal, deposit and loan transactions with customers.
Banks which use this system have many branches; each branch has a unique name, unique address and phone.
The system stores information about customers as unique customer ID, name, address, and phones.

88. ERD Narrative ( Cont’d)
Each customer has one Account identified by unique Account number, amount, last transaction date (Day, Month and Year).
The system records Transaction number, Transaction type, Transaction date, Transaction amount and time. The system records the branch name where the transaction occurred.
A Customer can make any type of transactions (Withdrawal or Deposit) from any branch of the bank.

89. An Example
A company is organized into departments. Each department has a unique name, a unique number, and a particular employee who manages the department. A department may have several locations.
A department may control a number of projects, each of which has a unique name, a unique number, and a single location. A project must controlled by department

90. An Example (Cont’d)
We store employee’s name, social security number, address, salary, gender and birth date. An employee must be assigned to one department and must work on one or more projects, which are not necessarily controlled by the same department. We keep track of the number of hours per week that an employee works on each project. We also keep track of the direct supervisor of each employee.
We want to keep track of the dependents of each employee for insurance purposes. We keep each dependent’s first name, gender, birth date and relationship to that employee.

92. ERD Case Study
An organization makes many models of cars, where a model is characterized by a unique name and a suffix (such as GL or XL) and an engine size.
Each model is made up from many parts and Each part has a description , an id code, production year, and many images.
each part may be used in the manufacturing of more than one model

93. ERD Case Study
Each model must be produced at just one of the firm's factories, which are located in London, Birmingham, Bristol, Wolverhampton and Manchester - one in each city. Each factory has number of machines, capacity, and computer system used ( OS , DBMS, Internet).
A factory produces many models of cars and many types of parts.
although each type of part is produced at one factory only and the model is produced in the same factory.

94. ERD Case Study 2
A country bus company owns a number of buses. A bus is characterized by number, No. of Chairs, Options ( AC , Automatic, PS) , and brand-name
Each bus is allocated to a particular route, although some routes may have several buses . Each route is described by KM, start point, end point and the duration.

95. ERD Case Study 2 Each route can passes through a number of towns.
A town may be situated along several routes. We keep track of unique name and station names in each town.
One or more drivers are allocated to one route during a period of time. The system keep information about the driver name , mobile number , hire date, basic salary , job grade.
The system keep information about any changes in the allocations of the drivers to the routes.

96. ERD Narrative: Lab
A database for a banking system is used to control withdrawal, deposit and loan transactions with customers.
Banks which use this system have many branches; each branch has a unique name, unique address and phone.
The system stores information about customers as unique customer ID, name, address, and phones.

97. ERD Narrative ( Cont’d)
Each customer has one Account identified by unique Account number, amount, last transaction date (Day, Month and Year).
The system records Transaction number, Transaction type, Transaction date, Transaction amount and time. The system records the branch name where the transaction occurred.
A Customer can make any type of transactions (Withdrawal or Deposit) from any branch of the bank.