database management systems cs403 power point slides lecture 07
TRANSCRIPT
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DatabaseDatabaseManagement Management
SystemSystem
Lecture - 7
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Entity-Relationship Data Model
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E-R Data Model
A semantic data model, used for the graphical representation of the conceptual database design
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Major Components
Entities
Attributes
Relationships
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Entity
Term used to mean three different meanings Entity type Entity instance Entity set
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Entity TypeA name/label assigned to
items/objects that exist in an environment and that have similar properties
It could be person, place, event or even concept
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Entity TypeDistinguishable from other entity
types on the basis of properties Identified through abstraction
processDifferent from External Entity
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Entity Instance & SetA particular object belonging to
a particular entity typeEntity Type: EmployeeEntity Instance: M. SharifEntity Set: All employees
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Types of Entity Types
Entity types can be classified into regular/strong/independent ETs or weak/dependent ETs
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Weak Entity Types An entity type whose instances
cannot exist without being linked with instances of some other entity type, i.e., they cannot exist independently
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Strong Entity TypeA strong/regular entity type is the
one whose instances can exist independently, i.e., without being linked to other instances
Strong ETs have their own identity
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Naming Entity Types Singular noun recommendedOrganization specific namesWrite in capitals Abbreviations can be used,
be consistent
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SymbolsRegular Entity Type
Weak Entity Type
NAME
NAME
EMPPLOYEE DEPENDENTS
BOOK BOOKCOPY
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Attribute An attribute of an entity type is a
defining property or quality of the instances of that entity type. Entity instances of same entity type have the same attributes. (e.g. Student Identification, Student Name)
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Domain of an Attribute
Every attribute has a domainSet of possible values for an
attributeThe attributes in an entity set get
the values from the same domain
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Types of Attributes
Single vs composite
Single valued vs multi-valued
Stored vs derived
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Symbols for Attributes
Each represented as an oval, linked with an ET symbol
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Symbols for Attributes
SimpleComposite
Multi-valued
Derived
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Example
EMPLOYEE
empId empNameExperience
emp_Qual streetdateHired houseNo
address
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Thanks
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DatabaseDatabaseManagement Management
SystemSystem
Lecture - 7