CHAPTER 3 Entity Relationship Modelling

CHAPTER 3 Entity Relationship Modelling

1. 2.0 Entity Relationship Model Concept

   • 3 Basic Concepts E-R model
     • 2.1. Entity Type
       • Is an object or concept that is identified by an organization where its existence is independence
       • entity
         • represent the object or concept being model uniquely
         • 2 types of entity
           • strong entity
             • whose existence is independent
           • weak entity
             • whose existence is dependent on some other entity
     • 2.2 Attributes
       • represent the properties of an entity or a relationship type
       • attribute domain
         • nilai yg represent satu satu entity
       • candidate key
         • attribute yg unik dicalonkan menjadi kunci
       • primary key
         • kena pilih drpd candidate key. bila dah confirm pilih so dia jadi PK.
         • kena yg unik
       • alternate key
         • yg tk terpilih dlm PK akan jadi AK
       • composite key
         • a candidate key that consist of two or more attributes
       • foreign key
         • ex: entity yg hubungan one, kena pinjamkan key
       • super key
         • mcm composite key
       • attributes categories
         • simple attribute
           • single component with an independent existence
             • ex: attribute tu tkleh pecah dah mcm StaffNo
         • composite attribute
           • multiple component, with independent existence
             • ex: dlm satu entity boleh ada bnyk pecahan ex StaffAddress
         • single-valued attribute
           • an attribute holds a single value for a single entity
             • ex dia tak ada dua nama. ada satu je la nilai
         • multi-valued attribute
           • holds multiple value for a single entity
             • ex: sorang tu ada bnyk no fon
         • derived attribute
           • value yang kita tak key in
           • datang drpd attribute yg lain. kamu x boleh isi
             • ex: maklumat 'age' tahu drpd 'birthday'
     • 3. Relationship Type
       • a meaningful association among entity types
       • Relationship Types
         • strong
         • weak
       • Degree of Relationship
         • it is a number of entities in relation
           • binary 2
           • unary 1
           • ternary 3
           • quaternary 4
       • Recursive Relationship
         • the same entity participates more than once in different roles
           • 1 entity tapi ada peranan berbeza
             • ulang balik pada diri sendiri

2. 3.0 Structural Constraints

   • 2 Types
     • Cardinality Constraint
       • determine the number of possible relationship for each ratio
         • 1:1
         • 1:M
         • M:M
     • Participation Constraint
       • whether the existence