Database Definition and DBMS

                                      EVERYTHING ABOUT INTERNET

1.Internet:

It is a global network connecting millions of computers.

More than 190 countries are linked into exchanges of data, news, and opinions.

According to Internet Live stats as of DEC 30 2014 there are 3,037,608,300 Internet users worldwide

We generally connect internet through Internet Service Provider [ISP].

Who Owns the Internet?

No single person or organization controls the Internet in its entirely. The Internet is more of a concept than an actual tangible entity, and it relies on a physical infrastructure that connects networks to other networks.

Is Web and Internet the Same?

The Internet is not synonymous with World Wide Web. The Internet is a massive network of networks, a networking infrastructure. It connects millions of computers together globally, forming a network in which any computer can communicate with any other computer as long as they are both connected to the Internet.

The World Wide Web, or simply Web, is a way of accessing information over the medium of the Internet. It is an information-sharing model that is built on top of the Internet.

2. World Wide Web:Tim Berners-Lee invented the World Wide Web in 1989
He founded and Directs the World Wide Consortium (W3C) the forum for technical development of the Web.

The World Wide Web is  system of Internet servers that supportspecially formatted documents. The documents are formatted in a markup language called HTML (HyperText Markup Language) that supports links to other documents, as well as graphics, audio, and video files. This means you can jump from one document to another simply by clicking on hot spots. Not all Internet servers are part of the World Wide Web.

There are several applications called web browsers that make it easy to access the World Wide Web.

The web is a way of accessing information over the medium of the internet. It is an information-sharing model that is built on top of the internet.

The web uses HTTP protocol, only one of the languages spoken over the internet, to transmit data.

Web services , which use HTTP to allow applications to communicate in order to exchange business logic , use the web to share information.

The web also utilizes browsers, such as Internet Explorer or Firefox, to access Web documents called web pages that are linked to each other via hyperlinks. Web documents also contain graphics , sounds, text and video.

The web is just one of the  ways that information can be disseminated over the internet. The internet not the web , is also used for e-mail , which relies on SMTP, usenet news groups, instant messaging and FTP. So the web is a portion of internet.

There are many organizations, corporations, governments, schools, private citizens and service providers that all own pieces of the infrastructure, but there is no one body that owns it all.

There are, however, organizations that oversee and standardize what happens on the Internet and assign IP addresses and domain names, such as the National Science Foundation, the Internet Engineering Task Force, ICANN, InterNIC and the Internet Architecture Board.

3. How to access documents?

With URL.

Abbreviation of Uniform Resource Locator (URL) it is the globaladdress of documents and other resources on the World Wide Web.

The first part of the URL is called a protocol identifier and it indicates what protocol to use, and the second part is called a resource name and it specifies the IP address or the domain name where the resource is located. The protocol identifier and the resource name are separated by a colon and two forward slashes.

For example, the two URLs below point to two different files at the domain pcwebopedia.com. The first specifies an executable file that should be fetched using the FTP protocol; the second specifies aWeb page that should be fetched using the HTTP protocol:

ftp://www.pcwebopedia.com/stuff.exe 
http://www.pcwebopedia.com/index.html

A URL is one type of Uniform Resource Identifier (URI); the generic term for all types of names and addresses that refer to objects on the World Wide Web.

The term "Web address" is a synonym for a URL that uses the HTTP / HTTPS protocol.

The Uniform Resource Locator (URL) was developed by Tim Berners-Lee in 1994 and the Internet Engineering Task Force (IETF) URI working group. The URL format is specified in RFC 1738 Uniform Resource Locators (URL).

4. IP address:

Internet protocol address.

An IP address is an identifier for a computer or device on a TCP/IPnetwork. Networks using the TCP/IP protocol route messages based on the IP address of the destination.

The Format of an IP Address

The format of an IP address is a 32-bit numeric address written as four numbers separated by periods. Each number can be zero to 255. For example, 1.160.10.240 could be an IP address.

Within an isolated network, you can assign IP addresses at random as long as each one is unique. However, connecting a private network to the Internet requires using registered IP addresses (called Internet addresses) to avoid duplicates.

An IP address can be static or dynamic. A static IP address will never change and it is a permanent Internet address. A dynamic IP address is a temporary address that is assigned each time a computer or device accesses the Internet

The four numbers in an IP address are used in different ways to identify a particular network and a host on that network. Four regional Internet registries -- ARIN, RIPE NCC, LACNIC and APNIC-- assign Internet addresses from the following three classes:

Class A - supports 16 million hosts on each of 126 networks
Class B - supports 65,000 hosts on each of 16,000 networks
Class C - supports 254 hosts on each of 2 million networks

The number of unassigned Internet addresses is running out, so a new classless scheme called CIDR is gradually replacing the system based on classes A, B, and C and is tied to adoption of IPv6. In IPv6 the IP address size is increased from 32 bits to 128 bits.

What is My IP Address?

To view your IP address you can use the ipconfig (IPCONFIG) command line tool.  Ipconfig displays all current TCP/IP network configuration values and refreshes Dynamic Host Configuration Protocol (DHCP) and Domain Name System (DNS) settings

5. Domain Name:

Domain names are used to identify one or more IP addresses. For example, the domain name microsoft.com represents about a dozen IP addresses. Domain names are used in URLs to identify particularWeb pages. For example, in the URLhttp://www.pcwebopedia.com/index.html, the domain name ispcwebopedia.com.

Every domain name has a suffix that indicates which top level domain (TLD) it belongs to. There are only a limited number of such domains. For example:

  gov - Government agencies

  edu - Educational institutions

  org - Organizations (nonprofit)

  mil - Military

  com - commercial business

  net - Network organizations

  ca - Canada

  th - Thailand

Because the Internet is based on IP addresses, not domain names, every Web server requires a Domain Name System (DNS) server to translate domain names into IP addresses.

6. Dynamic URL:

A URL that results from the search of a database-driven Web site or the URL of a Web site that runs a script. In contrast to static URLs, in which the contents of the Web page do not change unless the changes are coded into the HTML, dynamic URLs are generated from specific queries to a site's database. The page is merely a template to display the results of the query. Most of the content comes from the database that is associated with the site. Instead of changing information in the HTML code, the data is changed in the database.

Dynamic URLs often contain the following characters: ?, &, %, +, =, $, cgi-bin, .cgi.

A dynamic URL is the address of a dynamic Web page.

obfuscated URL

Also called a hyperlink trick, an obfuscated URL is a type of attack where the real URL that a user is directed to is obfuscated - or concealed - to encourage the user to click-through to the spoof Web site. For example, the attacker may use a cleverly misspelled domain name (e.g. PayPals.com instead of PayPal.com), or hide the actual URL in friendly text, such as "click here to verify your account now". Obfuscated URLs are commonly used in phishingattacks and other spam e-mails.

OPEN URL:

The OpenURL standard is a syntax to create Web-transportable packages of metadata and/or identifiers about an information object. OpenURL provides a mechanism for encoding a citation for an information resource, typically a bibliographic resource, as a URL. The OpenURL is, in effect, an actionable URL that transports metadata, or keys to access metadata, for the object for which the OpenURL is provided. The target of the OpenURL is an OpenURL resolver that offers context sensitive services based on that metadata. The OpenURL resolver is sometimes referred to as the user's Institutional Service Component (ISC). [* Source: A Simple OpenURL Resolver]

6. How do Web Servers WORK:

Have you ever wondered just exactly how this Web page you are reading found its way into your browser and onto your computer screen? The process largely depends on Web servers

Typically, users visit a Web site by either clicking on a hyperlink that brings them to that site or keying the site's URL directly into the address bar of a browser. But how does the same site appear on anyone's computer anywhere in the world and often on many computers at the same time?

Let's use Webopedia as an example. You decide to visit Webopedia by typing its URL -- http://www.webopedia.com -- into your Web browser. Through an Internet connection, your browser initiates a connection to the Web server that is storing the Webopedia files by first converting the domain name into an IP address (through a domain name service) and then locating the server that is storing the information for that IP address (also see Understanding IP Addressing).

The Web server stores all of the files necessary to display Webopedia's pages on your computer -- typically all the individual pages that comprise the entirety of a Web site, any images/graphic files and any scripts that makedynamic elements of the site function.

Once contact has been made, the browser requests the data from the Web server, and using HTTP, the server delivers the data back to your browser. The browser in turn converts, or formats, the computer languages that the files are made up of into what you see displayed in your browser. In the same way the server can send the files to many client computers at the same time, allowing multiple clients to view the same page simultaneously.

7. WebServer Error Messages:

Errors on the Internet, and those annoying error messages, occur quite frequently — and can be quite frustrating — especially if you do not know the difference between a 404 error and a 502 error. Many times they have more to do with the Web servers you're trying to access rather than something being wrong with your computer. Here is a list of error messages (also called HTTP status codes) that you might encounter while surfing the Web and their respective meanings to help you figure out just what the problem is.

List of HTTP Response Codes:

400 Bad File Request	Usually means the syntax used in the URL is incorrect (e.g., uppercase letter should be lowercase letter; wrong punctuation marks).
401 Unauthorized	Server is looking for some encryption key from the client and is not getting it. Also, wrong password may have been entered. Try it again, paying close attention to case sensitivity.
403 Forbidden/Access Denied	Similar to 401; special permission needed to access the site -- a password and/or username if it is a registration issue. Other times you may not have the proper permissions set up on the server or the site's administrator just doesn't want you to be able to access the site.
404 File Not Found	Server cannot find the file you requested. File has either been moved or deleted, or you entered the wrong URL or document name. Look at the URL. If a word looks misspelled, then correct it and try it again. If that doesn't work backtrack by deleting information between each backslash, until you come to a page on that site that isn't a 404. From there you may be able to find the page you're looking for.
408 Request Timeout	Client stopped the request before the server finished retrieving it. A user will either hit the stop button, close the browser, or click on a link before the page loads. Usually occurs when servers are slow or file sizes are large.
500 Internal Error	Couldn't retrieve the HTML document because of server-configuration problems. Contact site administrator.
501 Not Implemented	Web server doesn't support a requested feature.
502 Service Temporarily Overloaded	Server congestion; too many connections; high traffic. Keep trying until the page loads.
503 Service Unavailable	Server busy, site may have moved ,or you lost your dial-up Internet connection.
Connection Refused by Host	Either you do not have permission to access the site or your password is incorrect.
File Contains No Data	Page is there but is not showing anything. Error occurs in the document. Attributed to bad table formatting, or stripped header information.
Bad File Request	Browser may not support the form or other coding you're trying to access.
Failed DNS Lookup	The Domain Name Server can't translate your domain request into a valid Internet address. Server may be busy or down, or incorrect URL was entered.
Host Unavailable	Host server down. Hit reload or go to the site later.
Unable to Locate Host	Host server is down, Internet connection is lost, or URL typed incorrectly.
Network Connection  Refused by the Server	The Web server is busy.

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8. What Is The Semantic Web?

Five years ago when you said "I found out about that on the Web,", everyone knew what you were talking about. By means of hyperlinking or using a Web search engine you found a Web site with information you wanted.

Today people may talk about the World Wide Web, Web 2.0 or theSemantic Web. There are a lot of misconceptions about their similarities and differences, and also where the technologies inherent to each overlap, if they overlap at all.  The biggest misconception is that the terms Semantic Web and Web 2.0 mean the same thing.

Web 2.0 Is Not the Semantic Web

Web 2.0 is all about people. It's a social thing. The second generation of the World Wide Web is focused on the ability for people to collaborate and share information online. Where the Web contains static HTML pages, Web 2.0 is dynamic, in that it serves applications to users and offers open communications with an emphasis on Web-based communities.

Web 2.0, because it focuses on people and communications, encompasses a large number of technologies and standards. AJAX, Ruby, XHTML, SOAP and many more. Here the technology is less important to people — they don't care about the standards and technologies running these applications, they just want the end result, which is social interaction in an attractive and easy-to-use application.

What is the Semantic Web?

Where Web 2.0 is focused on people, the Semantic Web is focused on machines. The Web requires a human operator, using computer systems to perform the tasks required to find, search and aggregate its information. It's impossible for a computer to do these tasks without human guidance because Web pages are specifically designed for human readers. The Semantic Web is a project that aims to change that by presenting Web page data in such a way that it is understood by computers, enabling machines to do the searching, aggregating and combining of the Web's information — without a human operator.

From Documents To Data

The Semantic Web is not a separate entity from the World Wide Web. It is an extension to the Web that adds newdata and metadata to existing Web documents, extending those documents into data. This extension of Web documents to data is what will enable the Web to be processed automatically by machines and also manually by humans. To do this RDF (Resource Description Framework) is used to turn basic Web data into structured data that software can make use of. RDF works on Web pages and also inside applications and databases.

Webopedia Definition: RDF Short for Resource Description Framework, RDF is a general framework for describing a Web site's metadata, or the information about the information on the site. It provides interoperability among applications that exchange machine-understandable information on the Web. RDF details information such as a site's sitemap, the dates of when updates were made, keywords that search engines look for and the Web page's intellectual property rights. Developed under the guidance of the World Wide Web Consortium, RDF was designed to allow developers to build search engines that rely on the metadata and to allow Internet users to share Web site information more readily. RDF relies on XML as an interchange syntax, creating an ontology system for the exchange of information on the Web.