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Database Application Design

Handout #8

February 25, 2000

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Course information

• Instructor: Dragomir R. Radev (radev@si.umich.edu)

• Office: 305A, West Hall

• Phone: (734) 615-5225

• Office hours: Thursdays 3-4 and Fridays 1-2

• Course page: http://www.si.umich.edu/~radev/654w00

• Class meets on Fridays, 2:30 - 5:30 PM, 311 WH

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Managing multi-user databases(cont’d)

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Concurrency control

• Lax and strict policies

• Atomic transactions (LUWs = logical units of work)– Example: customer+salesperson

• Concurrent transaction processing: interlocking

• Lost update problem

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Example

• User A:– Read item 100– Reduce by 5– Write item 100

• User B:– Read item 200– Reduce by 3– Write item 200

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Resource locking

• Locks: implicit, explicit

• Example: two users

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Example

• User A:– Lock item 100– Read item 100– Reduce by 5– Write item 100

• User B:– Lock item 100– Read item 100– Reduce by 3– Write item 100

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Example (cont’d)1. Lock item 100 for A

2. Read item 100 for A

3. Lock item 100 for B; cannot

4. Decrease 100 by 5

5. Write item 100 for A

6. Release A’s lock on 100

7. Lock item 100 for B

8. Read item 100 for B

9. Decrease item 100 by 3

10. Write 100 for B

11. Release B’s lock on 100

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Resource locking

• Serizalizable transaction– 2PL: growing phase, followed by a shrinking

phase

• COMMIT and ROLLBACK

• DEADLOCKS

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Transaction isolation levels

• Exclusive use

• Repeatable read: mix of shared and exclusive locks

• Dirty read: for reports which don’t necessarily need to contain the latest data

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Cursor types

• Forward only: changes made to earlier records are hidden

• Static: any changes are hidden

• Dynamic: all changes are visible

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Database recovery

• Reprocessing: uses database saves

• Rollback/Rollforward : uses transaction logs, before-images, and after-images

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Database security

• Users, groups, permissions, objects

• Permissions:– CONNECT: ALTER SESSION, CREATE

TABLE, CREATE VIEW

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Application security

• Usually done on the Web server

• ASP script modifies SQL statement:

SELECT *FROM EMPLOYEE<% WHERE EMPLOYEE.Name “=SESSION(“EmployeeName”)”%>

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Sharing enterprise data

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Enterprise DB architectures

• Teleprocessing systems

• Client-server systems

• File-sharing systems

• Distributed database systems: vertical and horizontal fragmentation

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Comparing distributed DB architectures

Unified database

Distributed databases

Single Nonpartitioned Nonreplicated

Partitioned Nonreplicated

Nonpartitioned Replicated

Partitioned Replicated

Increased security risk

Increased difficulty of control

Increased cost/complexity

Increased availability

Increased flexibility

Increased independence

Increased parallelism+

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Problems in downloaded databases

• Coordination

• Consistency

• Access control

• Computer crime

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On Line Analytic Processing (OLAP)

• Hypercubes, axes, dimensions, slices

• Values of a dimension are called members

• Levels: hierarchical organization: e.g., date, month, year

• CROSSJOIN ({Existing Structure, New Construction}, {California.Children, Nevada})

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OLAP SQLCREATE CUBE HousingSalesCube ( DIMENSION Time TYPE TIME, LEVEL Year TYPE YEAR, LEVEL Quarter TYPE QUARTER, LEVEL Month TYPE MONTH, DIMENSION Location, LEVEL USA TYPE ALL, LEVEL State, LEVEL City, DIMENSION HousingCategory, DIMENSION HousingType, MEASURE SalesPrice, FUNCTION AVG, MEASURE AskingPrice, FUNCTION AVG)

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KDD: Data Mining

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Association rules

• X Y

• 65% of all customers who buy beer and tomato sauce also buy pasta and chicken wings

• Support (X)

• Confidence (X Y) = Support(X+Y) / Support (X)

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Object-oriented data processing

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Introduction

• OOP objects: encapsulated structures with attributes and methods

• Interface + implementation

• Inheritance

• Polymorphism

• Transient and persistent objects

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Final project guidelines

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ChecklistIntroductionUser interviews/needs: table, reports, queries, formsInitial data modelER modelDecompositionSQL codeDocumentationEvaluation, Future workScheduleSustainabilitySnapshotsPresentationDemo

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Grading

• Project: 40%- design 10%- implementation 10%- documentation 10%- presentation+demo 10%

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Readings for next time

• Kroenke– Chapter 14: Sharing Enterprise Data

– Chapter 17: Object-Oriented Database Processing

• YRK (optional)– Chapter 14: Java and JDBC