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Python is the most common coding language and is widely used. It is a favourite tool along being a flexible and open-sourced language. Its massive libraries like- Numpy, Pandas, SciPy, Keras, Pytorch, Tensorflow, Scikit-Learn and e.t.c which are used for data manipulation and are very easy to learn for a beginner or for professionals who want to know.

Data Science is the broad field in which you can learn about many concepts like- Python and R programming, Statistics, Probability and other topics of Mathematics, Machine Learning Algorithms, Techniques, Data Visualization tools- Big Data, SQL, NoSQL, Apache-Spark, MongoDB, PowerBI and e.t.c.

To learn data science and their other concepts, I would suggest you CorpWin technologies Programs. Corwin is one of the best training platforms to learn data science in depth. They provide the best course curriculum in which you will get all essential concepts of data science like- Python and its massive libraries concepts, Mathematics concepts, Techniques of ML and e.t.c. 

Many students have difficulty in understanding pointers. The best way to understand pointers is through memory representation.

Whenever we declare a variable, the computer allocates some amount of memory corresponding to this particular variable. Pointers are variables that store the address of another variable

2Phase Lock in Distributed Database:

In this protocol, it is required that all the data items must be reached in a mutually independent manner, i.e. when one transaction is performing, then no other transaction should interrupt the process.

It requires both locks and unlocks being done in two phases:

• Growing Phase: Obtain locks that means when we are writing something on A and B, then we will take locks on A and B like below: W(A) and W(B)
• Shrinking Phase: Release locks, Unlock the objects in a row like unlock (A) and unlock (B)

But 2 PL won’t be able to solve other problems such as cascading rollback.

1. when we execute the java file, JVM is loaded into memory.
2. In JVM, first class loader starts which loads the class into memory, i.e. it divides the code intoRuntime Memory Area.
3. Runtime memory consists of:-

• a) Heap- All the objects in the program are stored in a heap.
• b) Stack- all the local and ref variables are in the stack.
• c) Method area- it is a permanent area. It consists of static variables, class definitions and fxns.
• d) Native code area- the code which is not a part of Java but is a part of the platform, ie., the operating system that's called native code
• e) Program counter register- holds the address of next instruction going to be executed.

4. After the class loader, execution engine (JIT) runs which translate bytecode to machine-operable code.

The software is the virtual component of the computer through which we are doing our work.

The software is classified as System software and Application Software.

System Software provides the platform for loading application software. System software is the one who controls the hardware and helps users to do their work. It is the soul of the computer system. Once the device is designed, system software is loaded to make it live.

It is similar to humans, where once the body (hardware) is built, the body attains its system software in the name of soul.

Without system software, the hardware is a dead body. And also without hardware, the software is useless.

Application software is a set of programs or commands written to do a user-specific task. Different people use different types of application software. Based on the user requirements, we load our application software on the primary system software. It is like the development of our mind and knowledge based on the situation, schooling, surroundings for a human being.

So generally hardware is the body of the computer, while system software and application software are considered as soul and mind of computer respectively.

In a computer, there are two major parts available namely hardware and software. both plays an important role in proper functioning of the computer. 

Hardware are the touchable and physical parts of the computer. Hardware are visible to the user and it is visible even to a blind man. It is like the body of computer. Hardware provides the basic skeleton to load and work with software.

Software are nothing but the imaginary parts or virtual parts of the computer. Software is more complex and unable to understand easily. It is like mind or soul of the computer. It can't be touched or damaged. After finishing the design of hardware, Software is loaded into it.

When the hardware and software are working together, it becomes a computer. Without software, computer hardware is just a electronic board with connections. Without hardware, software cannot be used and can be stored only in CD or Pen Drive.

Algorithm:

1) Create a stack to store operands (or values).

2) Scan the given expression and do following for every scanned element.

a) If the element is a number, push it into the stack.

b) If the element is a operator, pop operands for the operator from stack. Evaluate the operator and push the result back to the stack

3) When the expression is ended, the number in the stack is the final answer.

In many of the IT and Computer science formal courses, I have observed many of the topics are taught as independent unrelated threads. In order to get a deeper insight of the computer science, it is very much essential to understand how these thinking machines work and how the wisdom of many great minds have made it possible.

It is necessary to understand how such a complex machine is designed with a goal that something called software can make it do fascinating stuff. And in general, a computer system is not very much different than a human mind. Our mind stores the information what it receives via sensor organs like eye, ear, skin, tongue which are converted into electrical signals and a huge number of neuron present in brain process the information and finally take some action. Note that the language plays a very important role in the process as we think in our language and communicate with each other using a common language.

In the same way, a computer system also has something equivalent to human mind which is known as a microprocessor and which has its own language in which it thinks and takes actions. Again important thing to note is that the unlike mind it does not decide what to do but it knows if someone has given a set of instructions or command to it along with data then it can execute those commands or instructions on the given dataset and generate the desired results. These instructions can be entered to the microprocessor using its sensors like keyboard, mouse etc and it has just like human brain storage devices to keep information in persistent storage like hard disks, USB devices, SSD etc.

From above it can be related that the instructions given to microprocessor(think Intel x86, AMD) are in the language of the microprocessor and they are known as instruction set of that microprocessor. The simple instructions are like add, subtract, multiply, divide, load, store, move etc but these are only a fraction of the whole set and can be downloaded from the web to understand it at a deeper level. These instructions are nothing but series of bytes(8-bit) and the different bit patterns indicate the role of the instruction which microprocessor understand and then accordingly perform the given tasks, for example, add two numbers.

The software at a very high level is nothing but a collection of these instructions and the order of these instructions is the program logic which a programmer writes using high-level languages like C++, Java, C etc. The instructions are specific to a particular microprocessor and cannot be understood by other microprocessors.

The other interpretation of the above sentence is that any software written in any programming language is finally converted to the sequence of instructions for that processor where it is about to be run. This conversion of a high-level language program to the instruction set of target microprocessor is done by another software called "compiler". The task of the compiler is to first understand the program written in high-level programming language and convert it into the language of the machine i.e. machine instructions. These machine instructions are also provided in a human-readable form known as "Assembly Language". Assembly language is nothing but the sequence of human-readable English characters like add, sub, multiply etc and either compiler or another program known as assembler can convert these English characters to binary bytes or machine instructions. And finally, these binary interactions are given to microprocessor to execute the program logic. Always note that finally on the processor it is always the machine instructions which are binary eg. 11001010 and other than that it does not understand anything.

My next posts will start going deep on how microprocessor work and how it communicates with surroundings like RAM, HDD. Then we will go over the operating system, virtual memory etc in order to understand how a complete system finally work as we operate it using GUI based display units.

I. Hashing:

1. Hash Table Representation:

• Hash table is a data structure used for storing and retrieving data very quickly. Insertion of data in the hash table is based on the key value. Hence every entry in the hash table is associated with some key.
• Using the hash key the required piece of data can be searched in the hash table by few or more key comparisons. The searching time depends on the size of the hash table.
• The effective representation of dictionary can be done using hash table. We can place the dictionary entries in the hash table using hash function.

2. Hash Function:                                               

• Hash function is a function which is used to put the data in the hash table. Hence one can use the same hash function to retrieve the data from the hash table. Thus hash function is used to implement the hash table.
• An integer value is returned by the hash function, called hash key.

Example:

Consider that we want place some employee records in the hash table The record of employee is placed with the help of key: employee ID. The employee ID is a 7 digit number for placing the record in the hash table. To place the record 7 digit number is converted into 3 digits by taking only last three digits of the key.

If the key is 496700 it can be stored at 0^th position. The second key 8421002, the record of those key is placed at 2^nd position in the array.

Hence the hash function will be:

                                   H (key) = key%1000

Where key%1000 is a hash function and key obtained by hash function is called hash key.

• Bucket and Home bucket: The hash function H(key) is used to map several dictionary entries in the hash table. Each position of the hash table is called bucket.

The function H(key) is home bucket for the dictionary with pair whose value is key.

3. Types of Hashing Functions:

There are various types of hash functions that are used to place the record in the hash table:

i. Division or Modulus Method:

• The hash function depends upon the remainder of division.

• Typically the divisor is table length.

Example: If the record 54, 72, 89, 37 is placed in the hash table and if the table size is 10 then

h(key) = record % table size                                                                                                      

             4 = 54%10                                                                                

             2 = 72%10

             9 = 89%10

             7 = 37%10

ii. Mid Square:

In the mid square method, the key is squared and the middle or mid part of the result is used as the index.

If the key is a string, it has to be preprocessed to produce a number.

The formula for computing the hash key is:

h(key) = (key)² =è and Result = middle digits of squared number or key

Example: Consider that if we want to place a record 3111 then:

(3111)² = 9678321

For the hash table of size 1000

h(3111) = 783 (the middle 3 digits)

iii. Multiplicative hash function:

The given record is multiplied by some constant value. The formula for computing the hash key is-

h(key) = floor(p *(fractional part of key*A))

Where, p is an integer constant, and A is constant number.

Donald Knuth suggested to use constant A = 0.61803398987

Example: If key 107 and p = 50 then,

h(key) = floor(50*(107*0.61803398987))

                                = floor(3306.4818458045)

                                = 3306

At 3306 location in the hash table the record 107 will be placed.

iv. Digit Folding:

The key is divided into separate parts and using some simple operation these parts are combined to produce the hash key.

The formula for computing the hash key is:

h(key) = h(k1) +h(K2) +----

Where, h(k1), h(k2),… are separate parts used for computing key.

Example:

Consider a record 12365412 then it is divided into separate parts as 123, 654, 12 and these are added together

H(key) = 123+654+12

             = 789

The record will be placed at location 789.

v. Digit Analysis:

The digit analysis is used in a situation when all the identifiers are known in advance. We first transform the identifiers into numbers using some radix, r. Then examine the digits of each identifier. Some digits having most skewed distributions are deleted. This deleting of digits is continued until the number of remaining digits is small enough to give an address in the range of the hash table. Then these digits are used to calculate the hash address.

4. Collisions In Hash Table:

The hash function is a function that returns the key value using which the record can be placed in the hash table. Thus this function helps us in placing the record in the hash table at appropriate position and due to this we can retrieve the record directly from that location. This function need to be designed very carefully and it should not return the same hash key address for two different records. This is an undesirable situation in hashing.

Definition: The situation in which the hash function returns the same hash key (home bucket) for more than one record is called collision and two same hash keys returned for different records is called synonym.

Similarly when there is no room for a new pair in the hash table then such a situation is called overflow. Sometimes when we handle collision it may lead to overflow conditions. Collision and overflow show the poor hash functions.

For example,

Consider a hash function.

h(key) = recordkey%10 having the hash table size of 10

The record keys to be placed are:

131, 44, 43, 78, 19, 36, 57 and 77

Now if we try to place 77 in the hash table then we get the hash key to be 7 and at index 7 already the record key 57 is placed. This situation is called collision. From the index 7 if we look for next vacant position at subsequent indices 8,9 then we find that there is no room to place 77 in the hash table. This situation is called overflow.

5. Collision Resolution Techniques:

If collision occurs then it should be handled by applying some techniques. Such a technique is called collision handling technique.

There are two methods for detecting collisions and overflows in the hash table:

1. Chaining
2. Open addressing (linear probing)

The two more difficult collision handling techniques are:

1. Quadratic probing
2. Double hashing

II. CHAINING:

In collision handling method chaining is a concept which introduces an additional field with data i.e. chain. A separate chain table is maintained for colliding data. When collision occurs then a linked list(chain) is maintained at the home bucket.

Example:

Consider the keys to be placed in their home buckets are:

131, 3, 4, 21, 61, 7, 97, 8, 9

Then we will apply a hash function as  H(key) = key % D

Where, D is the size of table. The hash table will be:

Here D = 10

0

1

2

3

4

5                                                                                                                                                                    

6

7

8

9

A chain is maintained for colliding elements. For instance 131 have a home bucket (key) 1. Similarly key 21 and 61 demand for home bucket 1. Hence a chain is maintained at index 1.

III. OPEN ADDRESSING :

i. LINEAR PROBING:

• This is the easiest method of handling collision. When collision occurs i.e. when two records demand for the same home bucket in the hash table then collision can be solved by placing the second record linearly down whenever the empty bucket is found.
• When use linear probing (open addressing), the hash table is represented as a one-dimensional array with indices that range from 0 to the desired table size-1.
• Before inserting any elements into this table, we must initialize the table to represent the situation where all slots are empty.
• This allows us to detect overflows and collisions when we inset elements into the table. Then using some suitable hash function the element can be inserted into the hash table.

For example:

Consider that following keys are to be inserted in the hash table:

131, 4, 8, 7, 21, 5, 9, 29

Initially, we will put the following keys in the hash table.

We will use Division hash function. That means the keys are placed using the formula:

H(key) = key % table-size

H(key) = key % 10

For instance the element 131 can be placed at

H(key) = 131 % 10

             = 1

Index 1 will be the home bucket for 131. Continuing in this fashion we will place 4, 8, 7.

Index	Hash key
0
1	131
2
3
4	4
5
6
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