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

CENG 351 Instructor: Nihan Kesim Çiçekli Office: A308 Email: nihan@ceng.metu.edu.tr 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: http://cow.ceng.metu.edu.tr Teaching Assistants: Ali Anıl Sınacı Ayşegül Yaman CENG 351

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

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

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

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

Introduction to File management CENG 351

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

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

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

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

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

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

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

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

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

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

Basic File Processing Operations Opening Closing Reading Writing Seeking CENG 351

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

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

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