1. Chapter -2- Data Modeling Using the Entity-Relationship Model
Database Design
Chapter -2- Data Modeling Using the Entity-Relationship Model
References:
Prof. Mona Mursi Lecture notes

2. Database Design
Steps in building a database for an application: 1. Understand real-world domain being captured 2. Specify it using a database conceptual model (E/R,OO) 3. Translate specification to model of DBMS (relational) 4. Create schema using DBMS commands (DDL) 5. Load data (DML)
خطوات تصميم قواعد البيانات اتطبيق معين (بنك مثلا):
تحليل الاحتياج ودراسة الواقع.
تحديد المواصفات بواسطة نموذج تصوري (ER model).
ترجمة المواصفات لنموذج قاعدة بيانات.
عمل مخطط لتركيبة قاعدة البيانات (schema).
إنشاء النظام وتحميل البيانات.
Real-world
domain
Conceptual
model
DBMS data
model
Create
Schema
(DDL)
Load data
(DML)

3. Database Design Process
Requirement Analysis
Conceptual Design
Logical Design
Physical Design
مراحل تصميم قواعد البيانات:
تحليل الاحتياج
التصميم المفاهيمي ER (يشرح الكينونات للنظام والعلاقات بينها)
التصميم المنطقي (schema)
التصميم الفعلي (يتعلق بكيفية تخزين البيانات ومسارات الوصول إليها)

4. Entity Relationship Data Model
ER model was first developed by Peter Chen in1976.
It is a high-level conceptual data model.
ER model describes the users data requirements as relationships among a group of entities.
It represent the logical structure of databases.
Special graphical symbols are used to present entities and the relationships between them.

5. Entity Relationship Modeling
Identifying the entities.
Define the relationships among these entities.
Define the attributes and keys for each entity.
The ER diagram.

6. Entity-Relationship Model (E/R)
The Entity-Relationship model (ER) is a high-level description of the structure of the DB The Entity-Relationship Diagram (ERD) is a graphical model for representing the conceptual model for the data A E/R models the DB using three element types: - Entities - Attributes - Relationships

7. ERD Example

8. Entities
Entity:
The basic object that the ER model represent is an entity which is a thing in the real world.
Physical existence : like a person, employee, cars .
Conceptual existence : like job, course.
Entity type: Entities sharing the same attribute set.
It is described by its name and attributes.
Entities of the same entity type are called entity set.
الكينونة:
كائنات تمثل أشياء في الواقع
ممكن أن تكون موجودة بشكل حقيقي مثل الموظف
أو بشكل تصوري مثل المقرر

9. The particular properties that describes the entity.
Attributes
Attribute:
The particular properties that describes the entity.
e.g.: an employee is described by : name, age, address, salary , job.
* An entity will have a value for each of its attributes.
السمات (الخواص):
خواص مميزة تصف الكينونة
مثل:
الكينونة: الموظف.
السمات: الاسم، العمر،العنوان، الراتب، الوظيفة.
كل كينونة لها قيم خواصها

10. Entities & Attributes STUDENT COURSE STUDENT COURSE name DOB name
St_no
Tel_no
hours
number
STUDENT
COURSE

11. Attributes Attribute types :- Composite and Simple.
Single Valued and Multi valued.
Stored and Derived Attributes.
أنواع الخواص (السمات):
مركبة أو بسيطة.
وحيدة القيمة أو متعددة القيم
مخزنة أو مستمدة من خواص أخرى

12. Attribute Types Composite vs Simple
Composite attributes: divided into smaller subparts e.g. name divided into first, initial ,last.
Simple attributes: attributes that are not divisible e.g. salary.
Name
FirstName
MiddleName
LastName
SALARY
initial
FName
LName
الخواص المركبة
الخواص البسيطة
Area_cd
DOB
name no
St_no
Tel_no EX
STUDENT

13. Single Valued vs Multivalued
Single value : most attributes are of this type. E.g. age
Multivalued: set of values for the same Attribute . E.g. car colors, previous degrees.
Color
initial
FName
LName
الخواص ذات القيمة الوحيدة
الخواص ذات القيم المتعددة
Area_cd
DOB
name no
St_no
Tel_no EX
Mobile
STUDENT

14. Stored vs Derived Attributes
Stored attributes: regular attributes.
Derived attributes: are calculated from attributes of one or several related entities.
E.g. calculating the salary from the hours worked and number of hours.
BDate
Age
الخواص المخزنة
الخواص المستمدة
name
DOB
St_no
Tel_no
age
STUDENT

15. More Attribute Types
Null values: some entities may not have an applicable values for an attribute => a special value is created called Null. E.g. in the employee information the field of mobile number can have a null value because some employees do not have mobile phones.
Complex attributes: composite and multivalued attributes can be nested.
{} represents multivalued.
() represents composite attributes.
E.g. a person may have many certificate, each certificate has the subfields name, year and level. Therefore it is represented this way : {certificate (name, year, level)}
الخواص الخالية
الخواص المركبة

16. Example of Entity & Attributes
Name
Fname
Lname
Address
Street
City
Zip
Degree Id
STUDENT
Ssn
Age
Gpa
STUDENT id, (Fname,Lname), {degree},(street, city, zip), age, gpa, ssn

17. Entities
Entity Type: is a collection of occurrences of entities that have common properties. E.g. employees.
Entity Instance: is a single occurrence of an entity type. E.g. the student named Nora.
Entity Set: a collection of all entities of a particular entity type in the database at any point in time. E.g. Employee .
Employee refers to both the type of entity + the current set of all employees entity in the database.
مثلا الكينونه الموظفين هذه تسمى
entity type
هذه الكينونه فيها اكثر من خاصيه مثلا الأسم و العنوان و الراتب
الموظف احمد يسمى entity instant
مجموعه البيانات المدخله في جدول الموظفين من اسماء و عنواين و رواتب لكل الموظفين تسمى
Entity set
الموظف احمد راتبه و عنوانه مع بعض يسمى entity وهي نفس السجل record في الجدول

18. Entity Must have many instants in DB. Must have many attribute .
Represented as a rectangle box inside it the entity type name .
الكينونات:
يجب أن يكون لها حالات
يجب أن يكون لها خواص مميزة
تمثل برسم مستطيل

19. Entity
Doctor Ahmed manage a heart clinic in a hospital . Where is the entities types and relationships ?
Doctor , hospital  entity
Ahmad  instant
Manage  relationship
الكينونة
الدكتور أحمد يدير عيادة القلب في المستشفى
Doctor
Manage
hospital

20. Key Attributes of an Entity Type
Key attribute: is a key that identifies each entity uniquely, and has a distinct value . E.g. the name attribute in the company entity is unique.
primary key: The primary key uniquely identifies each record in the table
Candidate Key (CK): a set of attributes that uniquely identify an instance of an entity. E.g. Students can be identified by SSN or ID.
Composite Key: is a key made from more than one attribute. E.g. the flight can be uniquely identified by flight number and flight date.
Alternate Key (AK): is a candidate key that is NOT selected to be the primary key.
مفتاح الكينونة:
الفتاح الأساسي
المفتاح المرشح
المفتاح المركب
المفتاح البديل

21. Keys Example Student Birth date Student name Student _ id
المفتاح البسيط
Example of Simple key

22. Composite Key in ERD CLASS FLIGHT name Section_no hours crs_code
المفتاح المركب
FlightNo
Date
FLIGHT

23. Primary Key Attribute (PK)
Can be a single attribute or composite attribute.
Can be called identifier.
Weak entity may have no key.
Has the following criteria:
Should not change its value
Not null
خصائص المفتاح الأساسي:
يمكن أن يكون أحادي أو مركب
يسمى معرف (Identifier)
الكينونات الضعيفة قد لا يكون لها مفتاح- سنشرح ذلك لاحقا
المفتاح الأساسي لا يمكن تغيير قيمته ولا يمكن أن يكون خاليا

24. Strong & Weak Entity Types
A strong entity type is NOT existence-dependent on some other entity type. It has a PK. A weak entity type is an entity type that is existence-dependent on some other entity type. It does not have a PK.
الكينونات القوية والكينونات الضعيفة
الكينونات القوية لا يعتمد وجودها على وجود كينونات أخرى ولها مفتاح أساسي
الكينونات الضعيفة يعتمد وجودها على وجود كينونات أخرى وليس لها مفتاح أساسي

25. Weak Entity Type
The existence of a weak entity type depends on the existence of a strong entity set; it must relate to the strong entity type via a relationship type called identifying relationship.
The PK of a weak entity set is formed by the PK of its strong entity type, plus a weak entity type discriminator attribute (Partial key).
الكائنات الضعيفة يجب أن تعتمد على وجود علاقة لها مع كائنات قوية
المفتاح الأساسي للكائن الضعيف هو عبارة عن المفتاح الأساسي للكائن القوي ذا العلاقة معه مضافا إليه خاصية مميزة من الكائن لضعيف
LName
FName
gender
NAME
emp_no
DOB
has
EMPLOYEE
DEPENDENT

26. Values Sets (Domains) of Attributes
Domain: the set of values that might be assigned to the attribute for each individual entity.
e.g. ages of employees can be ( 16-70)
e.g. names is a set of alphabetical characters only
Not displayed in ER diagram.
المجال: مجموعة القيم الممكنة لكائن معين.
مثال: القيم الممكنة لعمر الموظف مثلا (16-70)
مثال: القيم الممكنة لاسم الموظف هي حروف فقط.
لا تظهر على رسم ER

27. Relationships Constrains on relationship type: Cardinality ratios:
The max number of relationships instance an entity can participate in.
The values of Cardinality ratios:
One to one(1:1).
One to many (1:N) many to one (N:1).
Many to many (M:N).
A student is enrolled in one or more courses and a course has many students in it. M N
STUDENT
Registers
COURSE N 1
TEACHER
Works-in
DEPARTMENT

28. Relationships Participation constrains:
The min number of relationships instance an entity can participate in.
Tow types of participation:
Total (every entity in the entity type must participate in the relationship).
Partial (some entities in the entity type participate in the relationship).
Every course must have a teacher but not every teacher must teach a course.
Teaches
Total
TEACHER
Partial
COURSE

29. Relationship ( min, max) constrains:
There used to replace both cardinality & Participation
Min value is minimum number of entity participation in a relationship.
0 : partial participation.
1 and more : total participation.
Max value is maximum number of entity participation in a relationship must have max >=1.
Teaches
TEACHER
COURSE
Is equivalent to:
(0,n)
(1,n)
Teaches
TEACHER
COURSE