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Motivation for usin 1 g a database

Motivation for usin 1 g a database. Why Use a Database. Data Management Example. Scenario You are a DVD store owner. You are a DVD store owner. Customers rent DVDs of movies. Several copies of each movie. Needs Which DVDs has a customer rented? Are any DVD overdue?

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Motivation for usin 1 g a database

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  1. Motivation for usin1g a database Why Use a Database --Motivation for using a database--

  2. Data Management Example • Scenario You are a DVD store owner. • You are a DVD store owner. • Customers rent DVDs of movies. • Several copies of each movie. • Needs • Which DVDs has a customer rented? • Are any DVD overdue? • When will a DVD become available? --Motivation for using a database--

  3. Solution: A File-based System • Edit rented.txt file Customer: Cindy Liu, Rented: Harry Potter, Due: Set. 19, 2007 . . . • Advantages • Text editors are easy to use • Simple to insert a record • Simple to delete a record --Motivation for using a database--

  4. Complication: Queries • Does not address needs Query: What movies has Cindy Liu rented? Execute (not quite right): Search for ‘Cindy Liu’. Search for ‘^\s+Customer:\s*Cindy\s+Liu\s*,\s+Rented:’. Query: Are any DVDs overdue? Execute: ??? • Requirements • Robust, sophisticated query language • Clear separation between data organization (schema) and data --Motivation for using a database--

  5. Complication: Queries • Lacks data integrity, consistency • Clerk misspells value/field Customer: Cindy Lui, Rented: Harry Potter, Deu: Sep. 19, 2007 • Inputs improper value, same value differently Customer: Cindy Liu, Rented: Harry Potter2, Due: Sep. 29, 2007 • Forgets/adds/reorders field Terms: weekly special Due: Sep. 19, 2007, Rented: Harry Potter • Requirements • Enforce constraints to permit only valid information to be input. --Motivation for using a database--

  6. Complication: Update • Add/delete/update fields in every record • Record store location. Customer: JD, Rented: Babe, Due: Sep. 19, 2007, Store: Bry • Modify customer to first and surname. First: Joe, Surname: Doe, Rented: Babe, Due: Sep. 29, 2004 • Add/delete/update new information collections • customer.txt file to record information Customer: Jane Doe, Phone: 5575 3344 • Requirements • Ability to manipulate the way data is organized. --Motivation for using a database--

  7. Complication: Multiple Users • Two clerks edit rented.txt file at the same time. 1) Ben starts to edit rented.txt, reads it into memory. 2) Sarah starts to edit rented.txt. 3) Ben adds a record. 4) Ben saves rented.txt to disk. 5) Sarah saves rented.txt to disk. Ben’s added record disappears! • Requirements • Must support multiple readers and writers. • Updates to data must (appear to) occur in serial order. --Motivation for using a database--

  8. Complication: Crashes • Crash during update may lead to inconsistent state. • Ben makes 250 of 500 edits to change Jane Doe to her preferred name Jan Doe. • Before he saves it, Windows crashes! • Requirements • Must update on all or none basis. • Implemented by commit or rollback if necessary. --Motivation for using a database--

  9. Complication: Data Physically Separate • Wants • Want to advise Austin Power’s fans about new A P’s movie. • Method • customer.txt contains addresses of customers. • Must merge with rented.txt to create mailing list. • Problems • Text editors incapable of such a merge (write a program) • Several Joe Jenkins • Requirements • Uniquely identify each customer. --Motivation for using a database--

  10. Complication: Security • Customers want to know how many times a movie has been rented. • Provide access to rented.txt, but not to customer field, how to I do that in an editor? • Underage clerks should not see history of R-rated rentals. • Keep two lists of rentals? • Requirements • Ability to control who has access to what information. --Motivation for using a database--

  11. Complication: Efficiency • All DVD store owners in Dublin get together • rented.txt file gets huge (gigabytes of data). • Slow to edit. • Slow to query for customer information. • Requirements • New data structures to improve query performance. • System automatically modifies queries to improve speed. • Ability of system to scale to handle huge datasets. --Motivation for using a database--

  12. Complication: New Needs • All DVD store owners in Dublin get together. • What pairs of movies are often rented together? • Calculate probability of movie combinations. • Do we need more copies of the Austin Powers movie anywhere? • Plot rental history of Austin Powers by store area. • Requirements • Collect and analyse summary data. • Use computer to mine for interesting trends. • Support access to data by sophisticated programs. --Motivation for using a database--

  13. File-based Systems - Overview • A DVD store owner develops a system based on files. DVD rental checkin program new DVD ordering program customer mailing program rented DVD file customer file inventory master file --Motivation for using a database--

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