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Jun 04, 2018

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    Database Management SystemsSeptember 2, 2008

    Lecture 3

    Sections 4.1-4.5Enhanced Entity-Relationship Diagrams

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    REVIEW

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    aka Extended Entity-Relationship Model adds Inheritance

    indicates that one entity type isan extension of another entity type

    often referred to as an IS-A relationship

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    http://www.agilemodeling.com/artifacts/classDiagram.htm

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    Inheritancedefines a subclass relationship A subclass inherits all properties (members) of the superclass

    This is the perspectiveof most modern programming languages

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    BA, C A Every B is also an A Every C is also an A

    all entities

    A

    B C

    everything true about a memberof a set is also true about anymember of its subsets.

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    PhoneID

    Name

    Major Class Dept Office

    PERSON

    IsASTUDENT PROFESSOR

    (not used in our textbook)

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    PhoneID

    Name

    Major Class Dept Office

    PERSON

    STUDENT PROFESSOR

    preferred notation: shows directionality of inheritance

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    PhoneID

    Name

    Major Class Dept Office

    PERSON

    STUDENT PROFESSOR

    The circle may be omitted when not needed.

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    Student and professor entities have allattributes defined for a person,plus additional attributes

    Keys are also inherited.

    Subtypes should not define new keys.Phone

    IDName

    Major Class Dept Office

    PERSON

    STUDENT PROFESSOR

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    Disjointness: an entity can bea member of at most one subtype

    a person may bea student or maybe a professor, butnot both

    Covering: every entity of the supertypemust also be a member of at least one subtype

    every person must be a professor ora student

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    BA, C A B C =

    all entities

    A

    B C

    no entity is in both B and C

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    BA, CA B C =

    all entities

    A

    B C

    an entity may be in both B and C

    overlapping = non-disjoint

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    BA, C A B C = A

    all entities

    B C

    every entity in A is also in B or C

    A

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    BA, CA B C = A

    all entities

    A

    B C

    some entities in A are not in B or C

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    IsA (triangle) notation:

    write disjoint and/or coveringnext to the triangle

    Subset notation,

    d in the circledisjointness

    o in the circle

    no disjointness (overlap)required participation from supertypeindicates a covering constraint

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    Every A can also be a B or a C, or both, or neither

    A

    IsA

    B C

    o

    A

    B C

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    Every A can also be a B or a C or but not both

    A

    IsA

    B C

    d

    A

    B C

    disjoint

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    Every A must be a B or a C or both

    A

    IsA

    B C

    o

    A

    B C

    covering

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    Every A must be a B or a C, but not both

    A

    IsA

    B C

    d

    A

    B C

    disjoint,

    covering

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    disjoint, covering inheritance:

    every car is a vehicleevery truck is a vehicleevery vehicle is either a car or a truckno vehicle is both a car and a truck

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    disjoint, non-covering inheritance:

    employees may be secretaries, technicians or

    engineers, but not more than one of these

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    non-disjoint, covering inheritance:

    every part is a manufactured part,or a purchased part,

    or both (a purchased, manufactured part)

    **How many attributes does a purchased, manufactured part have?** How would we model this in UML (C++ or Java)?

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    **Interpret this schema.

    ** Can you find a real-world example?

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    Multiple inheritance gives us a lattice,rather than a hierarchy

    Inheritance Lattice

    **Could we have engineering managers without defining the E_M class?

    (compare to previous example)

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    Union defines a type as the union of other types OWNER = PERSON COMPANY OWNER is called a union type or category

    OWNER is the subtype of the union of PERSON and COMPANY

    Not multiple inheritance an OWNER does not need all the

    attributes fromboth PERSON and COMPANY

    OWNER

    PERSON COMPANY

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    A

    B C

    d

    A

    B C

    B and C are subtypes of AB AB ABC A

    A is a subtype of BC

    ABC

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