Portable application is a different form of a normal software.The difference is that we dont have to install it like normal software inorder to use it,but can run it and use it like a installed software.Now most of the softwares are releasing their portable version.

Usually we install a software in order to use it.In portable application of that software a compressed zip file will be the installation file.When you click on the zip and unzip it the software will be temporarily installed in the computer.You can do all the functions of that software and once you close the window no trace will be left by the software in the system.Even registry entry will be erased.

for example lets take a file recovery software RECUVA

http://www.piriform.com/recuva/builds

we can see different kinds of installation file like

INSTALLER

PORTABLE

Download the portable version and put in a pen drive and carry it.

Suppose your friend is crying for a lost file because of accidental deletion.You can come as a rescuer.You will put your pen-drive on his/her system,run the portable application.Recover file and close the program!!

Thus for people who dont know about a recovery software your action will be like a magic!.They wont understand what you have done and no traces of that software will be in that system.now thats cool!!

There are many such portable applications.Even browsers like mozilla firefox are available in portable form.When you browse from Internet cafe you can use it.

for more portable application visit  http://portableapps.com

We know that we cannot directly download video from YouTube.But we can easily download it by other ways.Here i am teaching you how to download YouTube video in 3 different ways.I start with easy method first and then tough ones.

1.DOWNLOAD FROM A WEBSITE

This is a very easy method.

1.Go to youtube and take your video

2.Copy the URL of that video from address bar of browser.(.for example www.youtube.com/watch?v=9DkLLB2EEKA)

3.go to http://keepvid.com

4.Paste the URL and click "Download"

5.You will be asked which format you like.whether .flv or .mp4.Click on the desired option and download it.

*if this window doesnt appear just refresh the browser.It will come.Thus its a very simple method.But please keep in mind you must have a flv or mp4 player in your system.VLC player is the best.you can download from http://www.filehippo.com/download_vlc

2.DOWNLOAD USING A SOFTWARE

This is also a very easy method.All you need is a software using which you can download the video.There are many software available for this purpose.One such is Orbit Downloader.You can download it from filehippo.com .Once you install it, a plug-in will appear in the browser using which you can download directly from browser,or you can open the software and download.

*just make sure that the video buffering is complete.ie the video is completed in the browser.ie.we know that a pale red color bar will move ahead of the dark red.just let that pale red be completed.It means that the whole video is temporarily downloaded in the system.

3.DOWNLOAD WITHOUT ANY SOFTWARE

This is little more lengthy step.To do this first you must know the concept.Just as i said in the second step using a software,when you click on the YouTube video that video is actually getting downloaded temporarily in the system,and once you close the browser its cleaned or deleted.So in this step what we are going to do is to get that temporarily downloaded file and save it in our system forever!!

lets see how to do it

1.You must have Mozilla FireFox in your system

2.In firefox go to TOOLS>>Clear Recent History>>Clear now(select everything)

2.Play the YouTube video in firefox and let the pale red complete.Its not necessary that you have to watch that video full.All that is needed is that pale red bar is complete.

3.Without closing the window open a new tab or a new window of firefox.

4.Type in the address bar  about:cache and press ENTER

5.In the page that appears Copy the location of Cache directory ( example C:\Documents and settings\...)

*offline cache is not needed

6.go to START>>RUN>>and paste the location you copied in it and click OK

7.A window appears with many unknown file.Now our video file is in it somewhere!!1.The best way to know which is the video file is to look the size.So right click on the window and select Arrange Icons By>>size

8.Look for the last file which is usually the larget size (will be of MB size) and copy it

9.Paste on some other location.say desktop itself

10.right click on the file and select rename and rename it into a file like name.flv

*make sure the file extension is .flv

YES!!!...THIS IS OUR VIDEO FILE.Now IF you have a flv player like VLC media player you can enjoy your favorite video.

This is a little lengthy method.The same principle is used by other softwares also!ie.getting the temporary downlaoded file

anywas you get your video

ENJOY

Abstraction means giving on overall view of the system without bothering for intricacies of system within. A database abstraction is an abstraction for the user such that user is able to handle the same without going into the details of the database system. Database abstraction, this way, in an application programming interface (API) that establishes communication between a user-oriented computer application and databases. Examples of such API are MySQL, PostgreSQL, Oracle, SQLite etc. Database vendors supply their own interface compatible with their products. To make it compatible with other database application programmers develop code for other database interfaces that is to be supported. This form layers that reduce burden for users, by providing an API and hide database internal behind this interface. As far as possible, user is kept free from bothering about the internals of the database.

Numerous abstraction layer are created with different interface is different programming languages. Oriented database system (ODBS) is an examples of a database abstraction layer for language. It is a database abstraction layer which is platform-independent. The user is required to install a particular drive- software, enabling ODBC to communicate with a database or set or databases. Thus program can also increase as statements are to be transformed into constructs understood by the target database.

Data in DBMS has three levels of abstraction. These are conceptual, physical and external schemas. A data definition language (DDL) defines the external schemas.

Data abstraction hides the complexity by creating an intermediates structure, called middleware, which is better organized. This creates an application that makes requests for data in well- organized an logical formate and thus user is made free from the burden of knowing its actual physical layout. This is like a person going to purchase few medicine with a list without bothering about how it is kept physically in the store. Similarly a user handling an application may request fir a customers record from the data abstraction layers and it fetches data from various data sources and transforms these is an agreed logical structure and then returns to the calling application.

Recovery Control in distributed database is based on the two-phase commit protocol. The two phase commit protocol is the transaction protocol duo to which all nodes and databases agree with each other to commit a transaction. This protocol is required in an environment where single transaction can interact with multiple independent resource managers as in case of distributed databases. It also support data integrity by ensuring that modifications made to transactions are either committed by all the databases involved in teh distributed system or rolled back by all the databases.

The two phases commit protocol works in two phases. The first phase is called the prepare phase during which the updates are recorded in a transaction log file, and the resource through a resource manager indicates that it is ready to make the changes. Resources can vote either to commit phase depend on the vote of resources. If all resources vote to commit then, all the resources participating in the transaction are updated whereas if one or more of the resources vote to roll back, then, all the resources are rolled back to their previous state.

Consider an example, in which an interaction between a coordinator at a local site and a participant at a remote site takes place and a transaction has requested the commit operation. In the first phase, the coordinator instructs the participants to get ready and sends the get ready message at time. Participants make an entry in it log and send the ok message as acknowledgement to  the coordinator. The coordinator then, writes an entry in the log, takes a final decision and sends it to the participants.