1. CENG 351 Introduction to Data Management and File Structures
Nihan Kesim Çiçekli
Department of Computer Engineering
METU
CENG 351

2. CENG 351 Instructor: Nihan Kesim Çiçekli Office: A308
Lecture Hours:
Section 1: Mon. 13:40, 14:40 (BMB4); Thu. 10:40 (BMB4)
Section 2: Wed. 9:40, 10:40 (BMB4); Thu. 11:40 (BMB3)
Course Web page:
Teaching Assistants: Ali Anıl Sınacı Ayşegül Yaman
CENG 351

3. References
Betty Salzberg, File Structures: An Analytic Approach, Prentice Hall, 1988.
Raghu Ramakrishnan, Database Management Systems (3rd. ed.), McGraw Hill, 2003.
Michael J. Folk, Bill Zoellick and Greg Riccardi, File Structures, An object oriented approach with C++, Addison-Wesley, 1998.
R. Elmasri, S.B. Navathe, Fundamentals of Database Systems, 4th edition, Addison-Wesley, 2004.
CENG 351

4. Course Outline Introduction: Secondary storage devices
Fundamental File Structure Concepts: Sequential Files
External Sorting
Indexed Sequential Files (B+trees)
Direct access (Hashing)
Introduction to Database Systems: E/R modeling, relational model,
Query languages: Relational algebra, relational calculus, SQL
Query Evaluation
CENG 351

5. Grading 3 written HWs, 3 programming assignments 30%
Midterm Exam 1 20%
Midterm Exam 2 20%
Final Exam 30%
Tentative Exam Dates:
Midterm Exam 1: Nov. 11, 2010
Midterm Exam 2: Dec. 23, 2010
CENG 351

6. Grading Policies Policy on missed midterm: Lateness policy:
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.
CENG 351

7. Introduction to File management
CENG 351

8. Motivation
Most computers are used for data processing. A big growth area in the “information age”
This course covers data processing from a computer science perspective:
Storage of data
Organization of data
Access to data
Processing of data
CENG 351

9. Data Structures vs File Structures
Both involve:
Representation of Data +
Operations for accessing data
Difference:
Data structures: deal with data in main memory
File structures: deal with data in secondary storage
CENG 351

10. Where do File Structures fit in Computer Science?
Application
DBMS
File system
Operating System
Hardware
CENG 351

11. Computer Architecture
data is manipulated here
- Semiconductors
- Fast, expensive, volatile, small
Main Memory (RAM)
data transfer
Secondary
Storage
- disks, tape
- Slow,cheap, stable, large
data is stored here
CENG 351

12. Advantages Disadvantages
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
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)
CENG 351

13. 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
CENG 351

14. Normal Arrangement
Secondary storage (SS) provides reliable, long-term 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.
CENG 351

15. 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.
CENG 351

16. 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.
CENG 351

17. 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;
CENG 351

18. Basic File Processing Operations
Opening
Closing
Reading
Writing
Seeking
CENG 351

19. 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.
CENG 351

20. 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
Name
Address
Student number
Gender
Age
GPA
Typically, each record in a file has the same fields.
CENG 351

21. Properties of Files
Persistance: Data written into a file persists after the program stops, so the data can be used later.
Sharability: Data stored in files can be shared by many programs and users simultaneously.
Size: Data files can be very large. Typically, they cannot fit into main memory.
CENG 351