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Relational Data Model

Relational Data Model. Ervi Bongso Alan Fernando CS157A. Outline. Sect. 6.4, Intro to Relational Algebra Comprise of: Unary Operations:  (selection) and  (projection) Binary Operations:  (union), - (difference),  (intersection), x (cartesian product) Natural Join: * and Join: ⋈

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Relational Data Model

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  1. Relational Data Model Ervi Bongso Alan Fernando CS157A

  2. Outline • Sect. 6.4, Intro to Relational Algebra Comprise of: • Unary Operations:  (selection) and  (projection) • Binary Operations:  (union), - (difference),  (intersection), x (cartesian product) • Natural Join: * and Join: ⋈ • Sect. 6.5, Views and Materialized Views • Sect. 6.6, Info of Preservation Issue

  3. Unary:  (selection) Extract a horizontal subset of tuples from a relation that matches specified search criteria. Age≥34(Person) Person Age=Weight(Person)

  4. Unary:  (projection) Extract a vertical subset of columns from a relation. Employee ∏name(Employee)

  5.  (selection),  (projection) Employee ∏name(бSalary>80,000(Employee))

  6. Binary:  (union) Adds the tuples from 1 relation to those from a second relation to produce a third relation. Student Professor Student  Professor

  7. Binary: - (difference) Contains the tuples from the first relation that are not in the second relation. Student Professor Professor - Student Student - Professor

  8. Binary:  (intersection) Contains tuples common to the two relations. Student Professor Student  Professor

  9. Binary: x (cartesian product) • Does not have to be union compatible. • Produces a new element by combining every tuple from one set with every tuple from the other set. R×S = R(A1,A2,...,An) × S(B1,B2,...Bm) = Q(A1,A2,...,An,B1,B2,...Bm) with degree n + m attributes

  10. Join: ⋈ • Used to combine related tuples from two relations into single tuples. • Allows us to process relationships among relations. • Example: to retrieve the name of the manager of each department: Step1) Dept_mgr ← Dept ⋈ Mgr_Ssn=SsnEmployee Step2) Result ← πDname, Lname, Fnamer(Dept_mgr)

  11. Example  Join: ⋈

  12. Natural Join: * • Created to get rid of the second attribute. • Requires that the two join attributes have the same name. • If not, renaming must first be applied. • Example: DEPT_LOCS ← DEPARTMENT * DEPT_LOCATIONS

  13. Example  Natural Join: *

  14. Views and Materialized Views • Views • Allows the same data to be seen by different users in different ways at the same time. • Provides security • Hides data complexity from the user. • Growth and Restructuring • Growth is expansion of existing relation schema. • Restructuring is changes other than growth.

  15. Views and Materialized Views (cont.) • Materialized Views (Snapshot) • Stored in the database. • Refreshed when updates occur. • Used to freeze data. • Deleted when it is not used for a period of time.

  16. Issue of Info Reservation

  17. References • Elamstri and Navathe, Fundamentals of  Database Systems, 5th ed., Addison-Wesley, 2008 • Umanath and Scamell, Data Modeling and Database Design, Thomson 2007 • http://www.cs.sjsu.edu/faculty/lee/cs157/cs157a.html

  18. Thank You!

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