Lecture 7 Data Compression File Structures

Previous Lecture

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

Today Lecture

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.

Outline Data Compression: how to make files smaller

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.

Using Compact Notation

Run-Length Encoding

Run-length Encoding Example

Variable-Length Codes

Huffman Code

Huffman Code Example

Huffman Tree

Irreversible Compression

Lempel-Ziv Codes

Lempel-Ziv Codes Example

Lempel-Ziv Codes Example

Lempel-Ziv Codes Example

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"

Next Lecture

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

Questions?