ics321-20090903-ER - ICS 321 Fall 2009 Introduction to...

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09/03/2009 Lipyeow Lim -- University of Hawaii at Manoa 1 ICS 321 Fall 2009 Introduction to Database Design Asst. Prof. Lipyeow Lim Information & Computer Science Department University of Hawaii at Manoa
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09/03/2009 Lipyeow Lim -- University of Hawaii at Manoa 2 Overview of Database Design Conceptual Design Use entity-relationship (aka ER) model represented pictorially as ER diagrams Map ER model to relational schema Questions to ask yourself What are the entities and relationships in the enterprise? What information about these entities and relationships should we store in the database? What are the integrity constraints or business rules that hold?
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09/03/2009 Lipyeow Lim -- University of Hawaii at Manoa 3 ER Model Basics: Entities Entity : Real-world object distinguishable from other objects. An entity is described (in DB) using a set of attributes . Entity Set : A collection of similar entities. E.g., all employees. All entities in an entity set have the same set of attributes. (Until we consider ISA hierarchies, anyway!) Each entity set has a key . Each attribute has a domain . Employees ssn name lot
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09/03/2009 Lipyeow Lim -- University of Hawaii at Manoa 4 ER Model Basics: Relationships Relationship : Association among two or more entities. Relationship Set : Collection of similar relationships. An n-ary relationship set R relates n entity sets E1 . .. En; each relationship in R involves entities e1 E1, . .., en En Same entity set could participate in different relationship sets, or in different “roles” in same set. lot dname budget did since name Works_In Departments Employees ssn
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09/03/2009 Lipyeow Lim -- University of Hawaii at Manoa 5 Cardinality Ratios of Relationships Consider binary relationships, i.e., between two entity sets Alternate notation: 1:1, 1:M, M:1, M:N Many-to-Many 1-to-1 1-to Many Many-to-1
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09/03/2009 Lipyeow Lim - University of Hawaii at Manoa 6 Internet Book Store Example Catalog of books ISBN, title, author, qty_in_stock, price, year_published Customers CID, Name, address Orders ISBN, CID, cardnum, qty, order_date, ship_date
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09/03/2009 Lipyeow Lim -- University of Hawaii at Manoa 7 Key Constraints Consider Works_In: An employee can work in many depts; a dept can have many employees. In contrast, each dept has at most one manager,
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ics321-20090903-ER - ICS 321 Fall 2009 Introduction to...

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