CENG%20352%20Database%20Management%20Systems

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CENG 352 Database Management Systems

• Instructor Nihan Kesim Çiçekli
• email nihan_at_ceng.metu.edu.tr
• URL http//www.ceng.metu.edu.tr/nihan

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CENG 352

• Instructor Nihan Kesim Çiçekli
• Office A308
• Email nihan_at_ceng.metu.edu.tr
• Lecture Hours Mon. 1440,1540 (BMB4) Thu.
  1340 (BMB2)
• Office Hours Fri. 1040-1130
• Course Web page http//www.ceng.metu.edu.tr/semr
  a/nli/ceng352
• Teaching Assistant Semra Dogandag
  (semra_at_ceng.metu.edu.tr)

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Text Books and References

1. Raghu Ramakrishnan, Database Management Systems,
   McGraw Hill, 3rd edition, 2003 (text book).
2. R. Elmasri, S.B. Navathe, Fundamentals of
   Database Systems, 4th edition, Addison-Wesley,
   2004.
3. A. Silberschatz, H.F. Korth, S. Sudarshan,
   Database System Concepts, McGraw Hill, 4th
   edition, 2002.
4. H. Garcia-Molina, J. D. Ullman, J. Widom,
   Database Systems The Complete Book, Prentice
   Hall, 2002.

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Grading

• Written assignments 15
• Project 20
• Midterm Exam 30
• Final 35
• Exam Date
• Midterm Exam 2nd week of April.

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Grading Policies

• Policy on missed midterm
• no make-up exam
• Lateness policy
• Late assignments are penalized up to 10 per day.
  
• All assignments are to be your own work. Projects
  in groups of two.

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Course Outline

• The Relational Data Model, Relational Algebra and
  Calculus, SQL
• Query Evaluation and Optimization
• Relational Database Design and Tuning
• Transaction Management, Concurrency Control and
  Crash Recovery
• Database Security and Authorization
• Parallel and Distributed Databases
• Object-Database Systems
• Information Retrieval and XML Data

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What is a Database Management System?

• A Database Management System (DBMS) is a software
  package designed to store and manage databases
• Manages very large amounts of data.
• 2. Supports efficient access to very large
  amounts of data.
• 3. Supports concurrent access to very large
  amounts of data.
• Example bank and its ATM machines.
• 4. Supports secure, atomic access to very large
  amounts of data.
• Contrast two people editing the same UNIX file
  last to write wins with the problem if two
  people deduct money from the same account via ATM
  machines at the same time new balance is wrong
  whichever writes last.

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Example Online Bookseller

• Data information on books (including
  categories, bestsellers, etc.), customers,
  pending orders, order histories, trends and
  preferences, etc.
• Massive many gigabytes at a minimum for
  medium-size bookseller, more if keep all order
  histories over all time, even more if keep images
  of book covers and sample pages
• gt Far too big for memory
• Persistent data outlives programs that operate
  on it
• Multi-user many people/programs accessing same
  database, or even same data, simultaneously
• gt Need careful controls

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Files vs. DBMS

• Application must stage large datasets between
  main memory and secondary storage (e.g.,
  buffering, page-oriented access, 32-bit
  addressing, etc.)
• Special code for different queries
• Must protect data from inconsistency due to
  multiple concurrent users
• Crash recovery
• Security and access control

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What is a Relational Database?

• Based on the relational model (tables)
• acct name balance
• 12345 Sally 1000.21
• 34567 Sue 285.48
• Today used in most DBMS's.

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The DBMS Marketplace

• Relational DBMS companies Oracle, Sybase are
  among the largest software companies in the
  world.
• IBM offers its relational DB2 system. With IMS,
  a nonrelational system, IBM is by some accounts
  the largest DBMS vendor in the world.
• Microsoft offers SQL-Server, plus Microsoft
  Access for the cheap DBMS on the desktop,
  answered by lite systems from other
  competitors.
• Relational companies also challenged by
  object-oriented DB companies.
• But countered with object-relational systems,
  which retain the relational core while allowing
  type extension as in OO systems.

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Three Aspects to Studying DBMS's

• 1. Modeling and design of databases.
• Allows exploration of issues before committing to
  an implementation.
• 2. Programming queries and DB operations like
  update.
• SQL intergalactic dataspeak.
• 3. DBMS implementation.

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Query Languages
Employee
Department
Name
Dept
Dept
Manager
SQL

• SELECT ManagerFROM Employee, DepartmentWHERE
  Employee.name "Clark Kent AND Employee.Dept
  Department.Dept
• Query Language Data definition language (DDL)
  like type defs in C or Pascal
• Data Manipulation Language (DML) Query
  (SELECT) UPDATE lt relation name gt SET
  ltattributegt lt new-valuegt WHERE ltconditiongt

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Host Languages
C, C, Java, Lisp, COBOL
Application prog.
DBMS
Calls to DB
Local Vars
(Memory)
(Storage)

• Host language is completely general (Turing
  complete)
• Query languageless general "non procedural" and
  optimizable

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Relational Model

• Relational model is good for
• Large amounts of data gt simple operations
• Navigate among small number of relations
• Difficult Applications for relational model
• VLSI Design (CAD in general)
• CASE
• Graphical Data

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Other Models

• Where number of "relations" is large,
  relationships are complex
• Object Data Model
• Logic Data Model
• OBJECT DATA MODEL
• 1. Complex Objects Nested Structure (pointers
  or references)
• 2. Encapsulation, set of Methods/Access functions
• 3. Object Identity
• 4. Inheritance Defining new classes like old
  classes
• Object model usually find objects via explicit
  navigation
• Also query language in some systems

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Other Models

• LOGIC (Horn Clause) DATA MODEL
• Prolog, Datalog
• if A1 and A2 then B
• B- A1 and A2
• Functions s(5) 6 (successor)
• Predicates with Arguments sum(X,Y,Z) ? X Y
  Z
• sum(X,0,X) means X 0 X (always true for all
  X)
• sum(X,s(Y),s(Z))-sum(X,Y,Z) means X(Y1)
  (Z1) if X Y Z
• More powerful than relational
• Can Compute Transitive Closure
• edge(X,Y).
• path(X,Y) - edge(X,Y).
• path(X,Z) - path(X,Y) edge(Y,Z).

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Data Models
60s 70's 80's 90s now
Hierarchical
Network
Relational
Choice for most new applications
Object Bases
Knowledge Bases
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Why Use a DBMS?

• Data independence and efficient access.
• Reduced application development time.
• Data integrity and security.
• Uniform data administration.
• Concurrent access, recovery from crashes.

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Data Independence

• Applications insulated from how data is
  structured and stored.
• Logical data independence Protection from
  changes in logical structure of data.
• Physical data independence Protection from
  changes in physical structure of data.

• One of the most important benefits of using a
  DBMS!

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Levels of Abstraction

• Many views, single conceptual (logical) schema
  and physical schema.
• Views describe how users see the data.
  
• Conceptual schema defines logical structure
• Physical schema describes the files and indexes
  used.

View 1
View 2
View 3
Conceptual Schema
Physical Schema

• Schemas are defined using DDL data is
  modified/queried using DML.

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Concurrency Control

• Concurrent execution of user programs is
  essential for good DBMS performance.
• Because disk accesses are frequent, and
  relatively slow, it is important to keep the cpu
  humming by working on several user programs
  concurrently.
• Interleaving actions of different user programs
  can lead to inconsistency e.g., check is cleared
  while account balance is being computed.
• DBMS ensures such problems dont arise users
  can pretend they are using a single-user system.

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Transaction An Execution of a DB Program

• Key concept is transaction, which is an atomic
  sequence of database actions (reads/writes).
• Each transaction, executed completely, must leave
  the DB in a consistent state if DB is consistent
  when the transaction begins.
• Users can specify some simple integrity
  constraints on the data, and the DBMS will
  enforce these constraints.
• Beyond this, the DBMS does not really understand
  the semantics of the data. (e.g., it does not
  understand how the interest on a bank account is
  computed).
• Thus, ensuring that a transaction (run alone)
  preserves consistency is ultimately the users
  responsibility!

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Scheduling Concurrent Transactions

• DBMS ensures that execution of T1, ... , Tn is
  equivalent to some serial execution T1 ... Tn.
• Before reading/writing an object, a transaction
  requests a lock on the object, and waits till the
  DBMS gives it the lock. All locks are released
  at the end of the transaction. (Strict 2PL
  locking protocol.)
• Idea If an action of Ti (say, writing X) affects
  Tj (which perhaps reads X), one of them, say Ti,
  will obtain the lock on X first and Tj is forced
  to wait until Ti completes this effectively
  orders the transactions.
• What if Tj already has a lock on Y and Ti later
  requests a lock on Y? (Deadlock!) Ti or Tj is
  aborted and restarted!

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Ensuring Atomicity

• DBMS ensures atomicity (all-or-nothing property)
  even if system crashes in the middle of a Xact.
• Idea Keep a log (history) of all actions carried
  out by the DBMS while executing a set of Xacts
• Before a change is made to the database, the
  corresponding log entry is forced to a safe
  location. (WAL protocol OS support for this is
  often inadequate.)
• After a crash, the effects of partially executed
  transactions are undone using the log. (Thanks to
  WAL, if log entry wasnt saved before the crash,
  corresponding change was not applied to database!)

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The Log

• The following actions are recorded in the log
• Ti writes an object The old value and the new
  value.
• Log record must go to disk before the changed
  page!
• Ti commits/aborts A log record indicating this
  action.
• Log records chained together by Xact id, so its
  easy to undo a specific Xact (e.g., to resolve a
  deadlock).
• Log is often duplexed and archived on stable
  storage.
• All log related activities (and in fact, all CC
  related activities such as lock/unlock, dealing
  with deadlocks etc.) are handled transparently by
  the DBMS.

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Databases make these folks happy

• End users and DBMS vendors
• DB application programmers
• e.g., smart webmasters
• Database administrator (DBA)
• Designs logical /physical schemas
• Handles security and authorization
• Data availability, crash recovery
• Database tuning as needs evolve

Must understand how a DBMS works!
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Structure of a DBMS
These layers must consider concurrency control
and recovery

• A typical DBMS has a layered architecture.
• The figure does not show the concurrency control
  and recovery components.
• This is one of several possible architectures
  each system has its own variations.

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Summary

• DBMS used to maintain, query large datasets.
• Benefits include recovery from system crashes,
  concurrent access, quick application development,
  data integrity and security.
• Levels of abstraction give data independence.
• A DBMS typically has a layered architecture.
• DBAs hold responsible jobs
  and are well-paid! ?
• DBMS RD is one of the broadest,
  most exciting areas
  in CS.