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section 1 - CS4320 Sections Fall 2011 Sections o Monday...

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Database Management Systems, R. Ramakrishnan and J. Gehrke 1 CS4320 Sections Fall 2011 ! Sections : o Monday, 7:30-8:20pm, Upson 315 (Section lead: Wenlei Xie) o Tuesday, 11:15-12:05pm; Upson 315 (Section lead: Tuan Cao) o Friday, 1:25-2:15pm; Upson 315 (Section lead: Ben Sowell) ! Instructor : Johannes Gehrke o Office hours: Fridays, 1:15-2:15pm, 4105B Upson Hall or by appointment. ! TAs : Tuan Cao, Qiming Fang, Keonseo Park, Ben Sowell, Wenlei Xie o Office hours: Mondays and Wednesdays, 5-6pm in 328B Upson Hall. o Please do not send emails to the TAs directly; you can contact the TAs by sending email to “cs4320-fall2011-tas-l at cornell.edu”.
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Database Management Systems, R. Ramakrishnan and J. Gehrke 2 Outline ! Review ER diagram modeling ! Do some ER diagram exercises e.g. Exercise 2.3 in the text book ! Finish up the Relational Algebra lecture ! Do some Relational Algebra and Calculus exercises e.g. Exercise 3.13 and Exercise 4.3 in the text book
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Database Management Systems, R. Ramakrishnan and J. Gehrke 3 Conceptual Design Using the ER Model ! Design choices: Should a concept be modeled as an entity or an attribute? Should a concept be modeled as an entity or a relationship? Identifying relationships: Binary or ternary? Aggregation? ! Constraints in the ER Model: A lot of data semantics can (and should) be captured. But some constraints cannot be captured in ER diagrams.
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Database Management Systems, R. Ramakrishnan and J. Gehrke 4 Entity vs. Attribute " Consider address information to the Employees entity set. " Should address be an attribute of Employees or an entity (connected to Employees by a relationship)? name Employees ssn lot
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Database Management Systems, R. Ramakrishnan and J. Gehrke 5 Entity vs. Attribute ! Depends upon the use and the semantics of the data: " Address as an attribute: - If we record only one address per employee. " Address as an entity: - If we have several addresses per employee, - If the structure (city, street, etc.) is important, e.g., we want to retrieve employees in a given city.
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Database Management Systems, R. Ramakrishnan and J. Gehrke 6 Entity vs. Attribute (Contd.) name Employees ssn lot Works_In4 from to dname budget did Departments Attributes “ from ” and “ to ” are used to record the interval during which an employee works for a department.
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Database Management Systems, R. Ramakrishnan and J. Gehrke
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