1. Lecture 7 Data Compression
File Structures

2. Previous Lecture

3. Field and record organization Sequential search and direct access
Lecture 6 Fundamental File Structure Concepts Managing Files of Records
Field and record organization
Sequential search and direct access
Seeking

4. Today Lecture

5. Overview
In this lecture, we continue to focus on file organization, but with a different motivation.
This time we look at ways to organize or re-organize files in order to improve performance.

6. Outline
Data Compression: how to make files smaller

7. Data Compression An Overview
Data Compression: Encoding the information in a file in such a way that it takes less space
Question: Why do we want to make files smaller?
Answer:
To use less storage, i.e., saving costs
To transmit these files faster, decreasing access time or using the same access time, but with a lower and cheaper bandwidth
To process the file sequentially faster.

8. Using Compact Notation

9. Run-Length Encoding

10. Run-length Encoding Example

11. Variable-Length Codes

12. Huffman Code

13. Huffman Code Example

14. Huffman Tree

15. Irreversible Compression

16. Lempel-Ziv Codes

17. Lempel-Ziv Codes Example

18. Lempel-Ziv Codes Example

19. Lempel-Ziv Codes Example

20. Assignment "aaabbcbcdddeab" "I AM SAM, SAM I AM"
Encode using Lempel-Ziv the file containing the following characters, drawing the corresponding digital tree
"aaabbcbcdddeab"
"I AM SAM, SAM I AM"

21. Next Lecture

22. Organizing Files for Performance
Reclaiming space in files
Sorting and Binary Searching

23. Questions?