what is proxy ?

Definition: proxy: In communications, a proxy is something that acts as a server, but when given requests from clients, acts itself as a client to the real servers. Analogy: Consider talking to somebody who speaks a foreign language through a translator. You talk to the translator, who receives your statements, then regenerates something else completely to the other end. The translator serves as your proxy. Key point: The communication terminates at the proxy. In other words, the proxy doesn't forward data so much as it tears it completely apart. For example, an HTTP proxy doesn't forward every request sent through it. Instead, it first examines if it already has the requested web page in its cache. If so, then it returns that page without sending another request to the destination server. Because proxies completely terminate the communication channel, they are considered a more secure firewall technology than packet filters, because they dramatically increase the isolation between the networks. Key point: You will occasionally be scanned for proxies. ISPs scan their users for proxies. Hackers scan the Internet looking for proxies they can anonymize their connections with. Certain servers (like IRC servers) scan clients for proxies in order to prevent anonymous connections. Several websites maintain lists of such proxies.

3-tier application

Courtesy : http://searchsoftwarequality.techtarget.com

A 3-tier application is an application program that is organized into three major parts, each of which is distributed to a different place or places in a network. The three parts are:
  • The workstation or presentation interface
  • The business logic
  • The database and programming related to managing it
In a typical 3-tier application, the application user's workstation contains the programming that provides the graphical user interface (GUI) and application-specific entry forms or interactive windows.
(Some data that is local or unique for the workstation user is also kept on the local hard disk.)
Business logic is located on a local area network (LAN) server or other shared computer. The business logic acts as the server for client requests from workstations. In turn, it determines what data is needed (and where it is located) and acts as a client in relation to a third tier of programming that might be located on a mainframe computer.
The third tier includes the database and a program to manage read and write access to it. While the organization of an application can be more complicated than this, the 3-tier view is a convenient way to think about the parts in a large-scale program.
A 3-tier application uses the client/server computing model. With three tiers or parts, each part can be developed concurrently by different team of programmers coding in different languages from the other tier developers. Because the programming for a tier can be changed or relocated without affecting the other tiers, the 3-tier model makes it easier for an enterprise or software packager to continually evolve an application as new needs and opportunities arise. Existing applications or critical parts can be permanently or temporarily retained and encapsulated within the new tier of which it becomes a component.
Contributor(s): Cheryl Gilbert
This was last updated in July 2000

OOPS Concept

Courtesy : http://www.java-questions.com

Q1) What is polymorphism?
Ans) Polymorphism gives us the ultimate flexibility in extensibility. The abiltiy to define more than one function with the same name is called Polymorphism. In java,c++ there are two type of polymorphism: compile time polymorphism (overloading) and runtime polymorphism (overriding).

The Best Free Online Project Management Software

By William Fenton

You're a small business looking to get organized. The technology's out there, you know that. The problem is you can't afford dedicated project management software. Or so you think. Luckily for you, I've waded through the Web to find four of the best options for small businesses on a budget. Forget cheap. It's got to be free. You have the right to remain organized whether you run OS XWindows 7, Red Hat, or some combination of the three, so I've only looked at online solutions. There will be plenty of opportunities to upgrade. Some might be worth it for your business. However, I'm interested in the top deals that don't demand a credit card.

Top 10 Open Source Web-Based Project Management Software


Project management software is not just for managing software based project. It can be used for variety of other tasks too. The web-based software must provide tools for planning, organizing and managing resources to achieve project goals and objectives. A web-based project management software can be accessed through an intranet or WAN / LAN using a web browser. You don't have to install any other software on the system. The software can be easy of use with access control features (multi-user). I use project management software for all of our projects (for e.g. building a new cluster farm) for issue / bug-tracking, calender, gantt charts, email notification and much more.

10 things you can do to boost PC performance

September 9, 2011, 2:17 PM PDT
Courtesy : Techrepublic.com

1: Get rid of malware

New machines shouldn’t have malware on them. But one of the most common causes of the “my PC used to be fast, and now it isn’t!” complaint is actually the presence of malware. Malware can sneak onto a computer in a zillion different ways and quite often it sits in the background slowing your machine to as it sends out spam emails, searches for other computers to infect, works on cracking cryptography, or any number of the other nefarious tasks that hackers like to use their botnet slaves for. There’s a good chance that the malware brought even more friends with it (that’s often how you see computers with thousands of viruses on them not long after the initial infection), and the infection may be bad enough to justify a wipe and reload. My first step in investigating a slow system is usually a virus scan.

Grid computing

Courtesy : Wikipedia

Grid computing is a term referring to the combination of computer resources from multiple administrative domains to reach a common goal. The grid can be thought of as a distributed system with non-interactive workloads that involve a large number of files. What distinguishes grid computing from conventional high performance computing systems such as cluster computing is that grids tend to be more loosely coupled, heterogeneous, and geographically dispersed. Although a grid can be dedicated to a specialized application, it is more common that a single grid will be used for a variety of different purposes. Grids are often constructed with the aid of general-purpose grid software libraries known as middleware.

Grid size can vary by a considerable amount. Grids are a form of distributed computing whereby a “super virtual computer” is composed of many networked loosely coupled computers acting together to perform very large tasks. Furthermore, “distributed” or “grid” computing, in general, is a special type of parallel computing that relies on complete computers (with onboard CPUs, storage, power supplies, network interfaces, etc.) connected to a network (private, public or the Internet) by a conventional network interface, such as Ethernet. This is in contrast to the traditional notion of a supercomputer, which has many processors connected by a local high-speed computer bus.

What is an IMEI number?

The IMEI (International Mobile Equipment Identity) is a unique 17 or 15 digit code used to identify an individual mobile station to a GSM or UMTS network. The IMEI number provides an important function; it uniquely identifies a specific mobile phone being used on a mobile network. The IMEI is a useful tool to prevent a stolen handset from accessing a network and being used to place calls. Mobile phone owners who have their phones stolen can contact their mobile network provider and ask them disable a phone using its IMEI number. With an IMEI number, the phone can be blocked from the network quickly and easily.

Read more: http://wiki.answers.com/Q/What_is_an_imei_number#ixzz167FGjwyY

Know about 3G

when mobiles ist came into existence they were referred to as 1G,then after some more elaborate and distinctive features the technology came to be known as 2g,and now with more wonderful features on the list,with a certain full movie download facility it is well said to be 3G.

Tell me more about 3G technology.

3G is the next generation mobile technology offering higher speeds on both uplink (up to 5.7 Mbps) and downlink (up to 28 Mbps). It will enable a host of rich multimedia services such as video calling, video on demand, and provide a richer experience for existing services such as mobile internet, mobile TV and MMS.
3G networks operate on technology called High Speed Downlink Packet Access (HSPA). Data is transmitted many times faster than earlier 2G networks. This basically means that in addition to the earlier audio, graphics, and text, you can now send and receive video content too — provided you have a 3G-enabled handset or USB datacard and are in 3G coverage areas.

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Uniq entry from a table in sql

The SQL DISTINCT clause is used together with the SQL SELECT keyword, to return a dataset with unique entries for certain database table column.


SELECT DISTINCT(id_email), email_name, email FROM emails LEFT JOIN emails_lists ON emails.id_email = emails_lists.fk_email WHERE email_valid = 1 AND fk_list IN ($fk_list)

Here's a handy query for finding duplicates in a table. Suppose you want to find all email addresses in a table that exist more than once:
SELECT email, 
 COUNT(email) AS NumOccurrences
FROM users
GROUP BY email
HAVING ( COUNT(email) > 1 )
You could also use this technique to find rows that occur exactly once:
SELECT email
FROM users
GROUP BY email
HAVING ( COUNT(email) = 1 )

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