Lempel–Ziv–Welch Compression

Lempel–Ziv–Welch (LZW) is a universal lossless data compression algorithm created by Abraham Lempel, Jacob Ziv, and Terry Welch. The algorithm is simple to implement, and has the potential for very high throughput in hardware implementations. It was the algorithm of the widely used Unix file compression utility compress, and is used in the GIF image format.Its works like index backside of our notebook.

• I am taking string pattern for elaboration to show compression.
• Make your choice that how much character you want to take, I am taking 4 character maximum for dictionary entry
  

Algorithms

Upper and Lower bound of a function

Upper Bound : Proving an upper bound means you have proven that the algorithm will use no more than some limit on a resource.

Lower Bound : Proving a lower bound means you have proven that the algorithm will use no less than some limit on a resource.


Upper and lower bounds have to do with the minimum and maximum "complexity" of an algorithm (I use that word advisedly since it has a very specific meaning in complexity analysis).

Take, for example, our old friend, the bubble sort. In an ideal case where all the data are already sorted, the time taken is f(n), a function dependent on n, the number of items in the list. That's because you only have to make one pass of the data set (with zero swaps) to ensure your list is sorted.

In a particularly bad case where the data are sorted in the opposite to the order you want, the time taken becomes f(n2). This is because each pass moves one element to the right position and you need npasses to do all elements.

Huffman Compression and Huffman Tree

Hi folks

We used ASCII code for represent character inside of computer. there are two types of ASCII 7 bit and 8bit.8bit ASCII is known as extended ASCII.

In 7 bit ASCII if represent text  following manner 

ABCDACDCAB     (Each character takes 7 bit)

Total Bit   = No. of character * 7

Total Bit   =  10*7

Total Bit   = 70

If consider frequency of character then we’ll find

Frequency of A = 3

Frequency of B = 2

Frequency of C = 3

Frequency of D = 2

In 7 bit ASCII we can represent 127 characters but it’s not always necessary that each character appeared in string as in our example string. There is only four characters which are repeated  so if we used 3 bit for code then we’ll save some bit

i.e. A=000

      B=001

      C=100

      D=101

Now total bit required 10*3 which is 30 instead of 70.

Database Key

Database is a repository of any organization data. It takes data save it and provides many types of sophisticated services for record insert, update, delete, backup and many more. Here I am interested to explain many types of key.

Database : Database is a collection of related table.

Table : A Table is a collection of related records.

Record : A record is a collection of related fields

Field : A fields or attribute is a smallest individual unit of table.

NULL : NULL is a systematic approach treat blank value which is not available current but might be appear in future.

Key : Key is use to identified a record between records set.