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CSE 344 -- Spring 2011
Lecture 13:   Conceptual Design

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Goal: design the right schema for a database that will persist for a
      long period of time.

ENTITY-RELATIONSHIP DIAGRAMS

   Entity Sets  = (draw box...)
   Attribute    = (draw oval...)
   Relationship = (draw diamond...)

Example: Online Event Database

*** In class:
   Entity sets: Users, Events, Response..

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Multiplicities of Binary E/R Relationships

   -- one-to-one
   -- one-to-many
   -- many-to-many

*** Question: which type of relationship is naturally represented in
    XML ?


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Multiway relationships

    Response: 
        - a relationship between User, User, Event
        - attribute Date


Converting a multiway relationship into binary relationships.


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Subclasses in E/R Diagrams

   E.g.  Organizer ISA User
         Invitee   ISA User


*** In class: show union types using subclasses

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Constraints in E/R Diagrams  = are statements that must always hold on
the data.  In E/R diagrams we have very limited constraints:

-- Keys
-- Referential integrity constraints
-- Degree Constraints

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Weak Entity Sets = when the key includes the key of some other entity
set