Entity Relationship Diagram2

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    Entity Relationship Diagram2 - Presentation Transcript

    1. ENTITY RELATIONSHIP DIAGRAM BY MEER SADAF NAEEM
    2. Part-1 Understanding the Fundamentals
    3. BASIC CONCEPTS
    4. WHAT IS ENTITY?
      • Person
    5. WHAT IS ENTITY?
      • Place
    6. WHAT IS ENTITY?
      • Object
    7. WHAT IS ENTITY?
      • Event
    8. ATTRIBUTES Descriptive properties possessed by each member of an entity set. Student Name Address Class Roll number Percentage
    9. ENTITY SET/TYPE: Student A Student B Student C Student D ENTITY SET : STUDENT
      • Set of entities of the same type that share the same attributes.
    10. STUDENT A STUDENT B STUDENT C STUDENT D Mr. A Mr.D Mr. C Mr. B ENTITY SET : STUDENT ENTITY SET : TEACHER
    11. What is relationship?
      • Meaningful association among several entities.
    12. RELATIONSHIP SET/TYPE: A set of relationships of the same type.
    13. Student A Student C Student B Mr. C Mr. B Mr. A ENTITY SET : STUDENT ENTITY SET : TEACHER RELATIONSHIP SET : SUBJECT
    14. DEGREE OF RELATIONSHIP SET The number of entity sets that participate in a relationship set.
    15. Student A Student C Student B Mr. C Mr. B Mr. A ENTITY SET : STUDENT ENTITY SET : TEACHER RELATIONSHIP SET : SUBJECT
    16. TYPES OF ATTRIBUTES
      • Single and composite:
          • roll number is an example of single attribute as it can not be divided further.
          • Name can be divided further into 3 parts consisting of first name , middle name , last name so it is an example of composite attribute .
    17. TYPES OF ATTRIBUTES
      • Single valued and multivalued:
            • The attributes which have single value are single valued attributes such roll number.
            • The attributes which has a set of values are called multivalued attributes . Such as any student can have more than 1 telephone number .
    18. TYPES OF ATTRIBUTES
      • Derived attribute:
            • These attributes are derived from the existing attributes of entities.
            • The value of a derived attribute is not stored , but computed when required.
    19. Student Name Address Class Roll number Date-of-birth
    20. TYPES OF ATTRIBUTES
      • Descriptive attribute:
            • The attribute of the relationship is called descriptive attribute.
    21. Cardinality
      • One to many
      • Many to one
      • One to one
      • Many to many
      • It expresses the number of entities to which another entity can be associated via a relationship set.
    22. ONE TO MANY A B a1 a4 a2 a3 b4 b3 b2 b1
    23. MANY TO ONE A B b2 a1 a2 a5 b3 b2 b1 a3 a4
    24. ONE TO ONE A B a1 a2 a3 a4 b4 b3 b2 b1
    25. MANY TO MANY A B a1 a3 a2 b4 b3 b2 b1 a4
    26. ROLE
      • Not specified when entity sets that participate in a relationship set are distinct.
      • Clarification is needed only when the entity sets of a relationship set are not distinct.
      The function that an entity plays in a relationship is called that entity’s role.
    27. RECURSIVE RELATIONSHIP
      • When entities are self-linked then such a relationship is called a recursive relationship.
    28. TOTAL PARTICIPATION
      • The participation of an entity set E in a relationship set R is said to be TOTAL if every entity in E participates in at least one relationship in R.
    29. Student A Student C Student B Mr. C Mr. B Mr. A ENTITY SET : STUDENT ENTITY SET : TEACHER RELATIONSHIP SET : SUBJECT
    30. PARTIAL PARTICIPATION
      • The participation an entity set E in a relationship set R is said to be PARTIAL if only some entities in E participate in relationships in R.
    31. MR.A MR.C MR.D MR.B CALCULUS JAVA DBMS FACULTY COURSES RELATIONSHIP SET:COURSE
    32. Design issues
      • Example : should location be an entity or attribute?
      • Can a project be in more than one location?
      • Does location need to be described in more detail?
    33. Weak entity set
      • Existence of weak entity set depends on the existence of a strong entity set which is called the identifying entity set.
      • The relationship is always many-to-one from weak to identifying.
      • Participation of the weak entity set in the relationship must be total.
      An entity set that does not have sufficient attributes to form a primary key is referred to as a weak entity set.
    34. Part-2 Introducing to Identifiers
    35. Identifiers
      • Candidate Key
        • All available unique , required identifiers of an entity
      • Primary Key
        • A unique, required identifier of an entity
        • The best one of candidate keys
      • Foreign Key
        • A reference key to another entity
        • This key is the primary key of another entity
    36. Primary Key
      • Natural primary key:
      • A natural primary key is one that exists in the data itself.
      • Surrogate primary key:
      • The primary key that you have created where non existed before.
      • Primary key requires the consideration not just of the current data, but of possible future data as well.
    37. Why is it important to identify primary key?
      • The primary key is the main “Handle” that the database server uses to grab the information in which you are interested.
      • By identifying a primary key, you are telling the server which information you want to work with at the moment.
    38. Foreign Key
      • A primary key of one table that is included in another table.
      • Links the records in one database table to another table.
    39.  

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