Skip to main content

ER Diagrams 1

The overall logical structure of a database can be expressed graphically by an ER diagram . It consists of
rectangles - which represents entity sets ,
ellipses - which represents attributes,
diamonds - which represents relationship among entity sets and
lines which links attributes to entity sets, attributes to relationship sets and entity sets to relationship. Each component is labeled with the entity or relationship or attribute it represents.
To distinguish among the four types of mapping cardinalities type, we shall draw either a directed or undirected line segment between the relationship set and the entity set.


Comments

Post a Comment

Popular posts from this blog

Writing a Bash Shell Script

What Are Shell Scripts? In the simplest terms, a shell script is a file containing a series of commands. The shell reads this file and carries out the commands as though they have been entered directly on the command line. The shell is somewhat unique, in that it is both a powerful command line interface to the system and a scripting language interpreter. As we will see, most of the things that can be done on the command line can be done in scripts, and most of the things that can be done in scripts can be done on the command line. Writing Your First Script And Getting It To Work To successfully write a shell script, you have to do three things: Write a script Give the shell permission to execute it Put it somewhere the shell can find it Writing A Script A shell script is a file that contains ASCII text. To create a shell script, you use a text editor . A text editor is a program, like a word processor, that reads and writes ASCII text files. There are...
Post a Comment
Read more

Basic Linux Commands For Beginner's

Basic Linux Commands for Beginners Linux is an Operating System’s Kernel. You might have heard of UNIX. Well, Linux is a UNIX clone. But it was actually created by Linus Torvalds from Scratch. Linux is free and open-source, that means that you can simply change anything in Linux and redistribute it in your own name! There are several Linux Distributions, commonly called “distros”. A few of them are: Mint Ubuntu Linux Red Hat Enterprise Linux Debian Fedora Kali Linux is Mainly used in Servers. About 90% of the Internet is powered by Linux Servers. This is because Linux is fast, secure, and free! The main problem of using Windows Servers are their cost. This is solved by using Linux Servers. Forgot to mention, the OS that runs in about 80% of the Smartphones in the World, Android, is also made from the Linux Kernel. Yes, Linux is amazing! A simple example of its security is that most of the viruses in the world run on Windows, but not on Linux...
4 comments
Read more

Shell

Definition of the Shell Shell is an interactive environment which provides an interface to an Operating System. It gathers input from user and execute the commands. Bourne shell(sh)- 1977 The Bourne shell was introduced. The Bourne shell(sh), by Stephen Bourne at AT&T Bell Labs for V7 UNIX, remains a useful shell today (in some cases, as the default root shell). The Bourne shell was developed after working on an ALGOL68 compiler, so its grammar is more along the lines of Algorithmic Language (ALGOL) than other shells. The source code was developed in C. The Bourne shell served two primary goals: Executing UNIX/Linux commands for the operating system,i.e, command line interpreter Writing reusable scripts that could be invoked through the shell,i.e, scripting In addition to replacing the Thompson shell, the Bourne shell offered many other advantages over its predecessors such as control flows, loops, and variables into scripts, providing a more functional language to...
Post a Comment
Read more