Relational Algebra - Selection, Projection, Joins etc

The relational algebra defines a set of operations on relations, paralleling the usual algebraic operations such as addition, subtraction etc which operate on numbers.The relational algebra operations take one or two relations (tables) as input and return a relation as output. This post we discuss the following relational operations:

1. Selection (σ)
2. Projection (π)
3. Cartesian product
4. Joins

Selection Operation (σ)

Diagonalisation Principle as Proving Technique - Tutorial with Examples

Diagonalisation principle is a mathematical method of proof. It is included in Theory of computation as a proving technique. The following is a download link to a PDF tutorial of Diagonalization principle.

Click here to download tutuorial as PDF

Storage Classes for Variables in C Programming Language

Every variable in C programming language has two properties; type and storage class. 'Type' refers to the data type of the variable such as integer, character, floating point values etc. It also deals with the size of the variable ( in bytes). 'Storage class' determines the part of memory where storage is allocated for the variable and how long the storage allocation continues to exist. It also determines the scope which specifies the part of the program over which a variable name is visible, i.e. the variable is accessible by name. The scope restriction can be overrode by making use of pointers. Whatever, in short, storage class is the property that determines the part of memory where storage is allocated, the lifetime of variable and the scope of the variable.

There are for storage classes in C programming:

• Automatic
• Register
• External
• Static

How to Connect PC or Laptop to Internet Using Android Phone

The Android operating system supports usage of Android phones as an Internet modem for Personal computer or laptops. This facility of sharing the Internet connection of Android phone with a laptop or PC through a USB cable is called USB tethering. It supports most of major operating systems.

In Linux:

In Linux you just have to enable 'packet data' in phone first, connect phone with PC or laptop through USB data cable and check the option 'USB tethering' in Settings. It is somewhere within USB settings or Wifi and network settings. The place of this option may vary from phone to phone.In my phone (Ssmsung Galaxy S Advance, GT-I9070) , it is found as follows: Settings-> Wireless and Neetwork->Tethering and Portable Hotspot-> USB tethering. Check the option 'USB Tethering'. When 'USB tethering' is enabled, your Linux OS will automatically install the 'Remote NDIS based Internet sharing' driver. and your computer will automatically connect to internet within a few minutes.

Windows XP:

How to Connect Windows 8 or 8.1 Compuer to Internet by USB Tethering Android Phone

Let me tell you first that USB tethering is the process of sharing the internet connection of your Android phone with your PC or laptop through USB connection. In Windows 7, Windows Vista and Linux, USB tethering works so easily that we just have to enable packet data, connect phone through USB and enable 'USB tethering' in Settings. Above mentioned operating systems automatically install the required drivers. And within few minutes, the system will connect to Internet through your USB connected Android phone. But it is not that much easy in Windows 8 or Windows 8.1. We have to manually install the driver for the Android device to enable USB tethering. In this post, I will show you how to enable USB tethering in Windows 8 and Windows 8.1.