Transcript 1-Introduction - COW :: Ceng

CENG 351
Introduction to Data Management
and File Structures
Nihan Kesim Çiçekli
Department of Computer Engineering
METU
CENG 351
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CENG 351-Section 2
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Instructor: Nihan Kesim Çiçekli
Office: A308
Email: [email protected]
Lecture Hours:
Tue. 9:40; Thu. 13:40,14:40 (BMB3)
• Course Web page: http://cow.ceng.metu.edu.tr
• Teaching Assistants:
Ömer Nebil Yaveroğlu
Nilgün Dağ
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References
1. Betty Salzberg, File Structures: An Analytic
Approach, Prentice Hall, 1988.
2. Raghu Ramakrishnan, Database Management
Systems (3rd. ed.), McGraw Hill, 2003.
3. Michael J. Folk, Bill Zoellick and Greg
Riccardi, File Structures, An object oriented
approach with C++, Addison-Wesley, 1998.
4. R. Elmasri, S.B. Navathe, Fundamentals of
Database Systems, 4th edition, Addison-Wesley,
2004.
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Course Outline
1. Introduction: Secondary storage devices
2. Fundamental File Structure Concepts:
Sequential Files
3. External Sorting
4. Indexed Sequential Files (B-trees)
5. Direct access (Hashing)
6. Introduction to Database Systems:
E/R modeling, relational model,
7. Query languages: Relational algebra, relational
calculus, SQL
8. Query Evaluation
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Grading
3 written HW, 3 programming assignments
Midterm Exam 1
Midterm Exam 2
Final Exam
30%
20%
20%
30%
Tentative Exam Dates:
Midterm Exam 1: Nov. 10, 2009
Midterm Exam 2: Dec. 22, 2009
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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 and programs are to be your own
work. No group projects or assignments are
allowed.
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Introduction to File management
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Motivation
 Most computers are used for data processing
(over $100 billion/year). A big growth area in
the “information age”
 This course covers data processing from a
computer science perspective:
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Storage of data
Organization of data
Access to data
Processing of data
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Data Structures vs File Structures
• Both involve:
– Representation of Data
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– Operations for accessing data
• Difference:
– Data structures: deal with data in main memory
– File structures: deal with data in secondary
storage
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Where do File Structures fit in
Computer Science?
Application
DBMS
File system
Operating System
Hardware
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Computer Architecture
data is
manipulated
here
Main Memory
(RAM)
- Semiconductors
- Fast, expensive,
volatile, small
data
transfer
data is
stored here
- disks, tape
Secondary
Storage
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- Slow,cheap,
stable, large
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Advantages
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Main memory is fast
Secondary storage is big (because it is cheap)
Secondary storage is stable (non-volatile) i.e.
data is not lost during power failures
Disadvantages
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Main memory is small. Many databases are too
large to fit in main memory (MM).
Main memory is volatile, i.e. data is lost during
power failures.
Secondary storage is slow (10,000 times slower
than MM)
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How fast is main memory?
• Typical time for getting info from:
Main memory: ~12 nanosec = 120 x 10-9 sec
Magnetic disks: ~30 milisec = 30 x 10-3 sec
• An analogy keeping same time proportion
as above:
Looking at the index of a book : 20 sec
versus
Going to the library: 58 days
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Normal Arrangement
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Secondary storage (SS) provides reliable, longterm storage for large volumes of data
At any given time, we are usually interested in
only a small portion of the data
This data is loaded temporarily into main
memory, where it can be rapidly manipulated
and processed.
As our interests shift, data is transferred
automatically between MM and SS, so the data
we are focused on is always in MM.
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Goal of the file structures
• Minimize the number of trips to the disk in
order to get desired information
• Grouping related information so that we are
likely to get everything we need with only
one trip to the disk.
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Physical Files and Logical Files
• physical file: a collection of bytes stored on a disk or
tape
• logical file: a "channel" (like a telephone line) that
connects the program to a physical file
• The program (application) sends (or receives) bytes
to (from) a file through the logical file. The program
knows nothing about where the bytes go (came from).
• The operating system is responsible for associating a
logical file in a program to a physical file in disk or
tape. Writing to or reading from a file in a program is
done through the operating system.
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Files
• The physical file has a name, for instance
myfile.txt
• The logical file has a logical name (a
varibale) inside the program.
– In C :
FILE * outfile;
– In C++:
fstream outfile;
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Basic File Processing Operations
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Opening
Closing
Reading
Writing
Seeking
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File Systems
• Data is not scattered hither and thither on
disk.
• Instead, it is organized into files.
• Files are organized into records.
• Records are organized into fields.
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Example
• A student file may be a collection of student
records, one record for each student
• Each student record may have several fields, such
as
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Name
Address
Student number
Gender
Age
GPA
• Typically, each record in a file has the same fields.
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Properties of Files
1) Persistance: Data written into a file
persists after the program stops, so the
data can be used later.
2) Sharability: Data stored in files can be
shared by many programs and users
simultaneously.
3) Size: Data files can be very large.
Typically, they cannot fit into main
memory.
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