Hi,Today Oracle is one of the most used language around the world of database.While studying about oracle,we must know about oracle DDBMS (Distributed Database Management System).

Here i am going to share some points about oracle DDBMS.

Oracle DDBMS does not support fragmentation transparency , but it can support location transparency. The funtionality of oracle DDBMS contains many elements like,

* Connectivity ( Connection between to destinations )

* Global Database names ( Database names around the world )

* Database links ( Link to access database quickly )

* Transactions ( Transfer of Data )

* Referential Integrity

* Distributed Query Optimization

Eventhough there are  many database tools like MS Access,PHP, are available , but still oracle is one of the outstanding tool for database management.

I think oracle will be the king of database tool in the future.

 

We have all downloaded files from the internet.You must have noticed that almost always, they are in .rar or .zip format i.e. they are compressed.Compression allows us to reduce the size of a file by up to 75%.

Now,the question that arises is, HOW IS IT DONE? Let me explain.

There are 2 types of compression:

1. Lossless Compresssion: In lossless compression,as the nae suggests,there is no loss i.e. the data is fully                 recovered on decompression. Eg. winRAR files,WinZip files.

2. Lossy Compresion: In lossy compression,there is a loss in the data while compression i.e. thecompressed file is never exactly equal to the original file. But, the loss is generally not noticable.Eg. MP3 files, JPEG pictures.

How does Lossless compression work?

The answer is just one word "redundancy" i.e. repetition of the same data again and again.

Let us consider an example:

"Democracy is government of the people,by the people,for te people".

If we consider a charater to occupy 2 bytes in the memory,then the sentence occupes 138 bytes. You might notice that the words "the" and "people" are reapeated 3 times. So, we create a dictionary by assigning a number to these words. Now we can use the numbers in place of these words. So the sentence becomes:

"democracy is government of 1 2, by 1 2,for 1 2."

The dictionary contains:---1: "the" ,  2: "people" .

Now,the sentence along with the dictionary occupies only 124 bytes. But, the compression program doesn't see this sentence as a group of words.It sees this as a collection of characters.So, its doesn't see which words are repeated. Instead,it sees which combination of charascters are repeated. So, it may take " the people" as a single unit. So ,the dictionary may contain "1 : the people".

Now the sentence becomes :

"Democracy is government of 1, by 1, for 1".

Now, the sentence along with the dictionary occupies only 104 bytes.Thus, we have achieved about 25% compression.And this is just one sentence! Imagine the compression in an entire article,chapter or even the entire book!.

The compression is much more in the programs written in programming languages like C++,java,visual basic,etc. where some keywords are repeated again and again. This was the simplest compression algorithm. There are many others like HoffMann coding and LZW algorithm.

Now,if you are really interested ,try compression this sentence:

"Ask not what your country can do for you,ask what you can do for your country".

This was about lossless compression.

Lossy compession works by removing informatin in such a way that it isn't noticeable. I may write about itnext time.

Just for information ,this article's size is 2842 bytes in .txt format and 1,143 bytes in .rar format(60% compression).

--Atul Barapatre

 

 

Java Developer Kit

 

It is a collection of tools and necessary documents for making Java applications and applets.

 

The JDK consists of :

1.the Java compiler javac.exe to convert Java program into bytecodes.

2.the Java interpreter java.exe to translate bytecodes into program action to be executed by the JVM.

3.the Java debugger jdb.exe to death Java programs.

4.the Java disassembler javap.exe to display certain specific interfaces.

5.the Java header file generator javah.exe.

6.the Java documentation javaDoc.exe.

7.applet viewer

 

I have noticed that many persons do not have the proper idea of what is done usually in software or IT companies. Even some of the students studying Information Technology also have doubts about it. To clarify the entire thing we need a brief discussion about this.

Most of the software companies do not involve themselves in creating public software like Photoshop, browsers, media players etc. They involve themselves in making software  for industrial use, e.g. Hotel Automation Software, Library Management Software, Banking software etc. Their work is contract based. When a company (such as a hotel) wants to automate their work, they contacts a software company and tells them about their requirements. In this step the software analyst  interviews the customer about their requirements and then removes all kinds of redundancies omissions and inconsistencies in that requirements. After all these have been done the entire thing is written in a document called SRS document.

Next, software building is started according to this document and after the entire software is built, the software is tested to check if it is working or not. After the customers approval the software product is sent to the customer.

Though the software building is complete, one phase continues for a long time - it is the longest phase of software development, called the maintenance. It concerns with improvement, error correction etc.

Thus in case of software engineering, no actual or physical product but a virtual product is built.