Predominant compensation methods in affiliate marketing

The following models are also referred to as performance based pricing/compensation model, because they only pay if a visitor performs an action that is desired by the advertisers or completes a purchase. Advertisers and publishers share the risk of a visitor that does not convert.

Pay-per-sale (PPS) - (revenue share)

Cost-per-sale (CPS). Advertiser pays the publisher a percentage of the order amount (sale) that was created by a customer who was referred by the publisher. This form of compensation is also referred to as revenue sharing.

Pay-per-lead (PPL)/pay-per-action (PPA)

Cost-per-action or cost-per-acquisition (CPA), cost per lead (CPL). Advertiser pays publisher a commission for every visitor referred by the publisher to the advertiser (web site) and performs a desired action, such as filling out a form, creating an account or signing up for a newsletter. This compensation model is very popular with online services from internet service providers, cell phone providers, banks (loans, mortgages, credit cards) and subscription services.

Special CPA compensation models

Pay-per-call

Similar to pay per click, pay per call is a business model for ad listings in search engines and directories that allows publishers to charge local advertisers on a per-call basis for each lead (call) they generate (CPA). Advertiser pays publisher a commission for phone calls received from potential prospects as response to a specific publisher ad.

The term "pay per call" is sometimes confused with click-to-call, the technology that enables the “pay-per-call” business model. Call-tracking technology allows to create a bridge between online and offline advertising. Click-to-call is a service which lets users click a button or link and immediately speak with a customer service representative. The call can either be carried over VoIP, or the customer may request an immediate call back by entering their phone number. One significant benefit to click-to-call providers is that it allows companies to monitor when online visitors change from the website to a phone sales channel.

Pay-per-call is not just restricted to local advertisers. Many of the pay-per-call search engines allows advertisers with a national presence to create ads with local telephone numbers. Pay-per-call advertising is still new and in its infancy, but according to the Kelsey Group, the pay-per-phone-call market is expected to reach US$3.7 billion by 2010.
Pay-per-install (PPI)

Advertiser pays publisher a commission for every install by a user of usually free applications bundled with adware applications. Users are prompted first if they really want to download and install this software. Pay per install is included in the definition for pay per action (like cost-per-acquisition), but its relationship to how adware is distributed made the use of this term versus pay per action more popular to distinguish it from other CPA offers that pay for software downloads. The term pay per install is being used beyond the download of adware[1].

Pricing models in search engine marketing

Pay-per-click (PPC)

Cost-per-click (CPC). Advertiser pays publisher a commission every time a visitor clicks on the advertiser's ad. It is irrelevant (for the compensation) how often an ad is displayed. commission is only due when the ad is clicked. See also click fraud.

Pay per action (PPA)

Cost-per-action (CPA). Search engines started to experiment with this compensation method in spring 2007.

Pricing modes in display advertising

Pay-per-impression (PPI)

Cost-per-mil (mil/mille/M = Latin/Roman numeral for thousand) impressions. Publisher earns a commission for every 1,000 impressions (page views/displays) of text, banner image or rich media ads.

Pay per action (PPA) or cost per action (CPA)

Cost-per-action (CPA). Used by display advertising as pricing mode as early as 1998 . By mid-2007 the CPA/Performance pricing mode (50%) superseded the CPM pricing mode (45%) and became the dominant pricing mode for display advertising .

Shared CPM

Shared Cost-per-mil (CPM) is a pricing model in which two or more advertisers share the same ad space for the duration of a single impression (or page view) in order to save CPM costs. Publishers offering a shared CPM pricing model generally offer a discount to compensate for the reduced exposure received by the advertisers that opt to share online ad space in this way. Inspired by the rotating billboards of outdoor advertising, the shared CPM pricing model can be implemented with either refresh scripts (client-side JavaScript) or specialized rich media ad units. Publishers that opt to offer a shared CPM pricing model with their existing ad management platforms must employ additional tracking methods to ensure accurate impression counting and separate click-through tracking for each advertiser that opts to share a particular ad space with one or more other advertisers.

Compensation methods in contextual advertising

Pay-per-click (PPC)

See PPC/CPC in Search engine marketing.

Pay-per-impression (PPI)

see PPI/CPM in Display Advertising

Google AdSense offers this compensation method for its "Advertise on this site" feature that allows advertisers to target specific publisher sites within the Google content network.

Compensation methods grid

There are different names used for the same type of compensation method and some compensation methods are actually special cases for another method. This grid shows alternative names for the individual compensation methods. The "cost per ..." name was used as default.

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Site Map and Biositemap

Easy to know about site map just for you to make better ...

A site map (or sitemap) is a representation of the architecture of a web site. It can be either a document in any form used as a planning tool for web design, or a web page that lists the pages on a web site, typically organized in hierarchical fashion. This helps visitors and search engine bots find pages on the site.

While some developers argue that site index is a more appropriately used term to relay page function, web visitors are used to seeing each term and generally associate both as one and the same. However, a site index is often used to mean an A-Z index that provides access to particular content, while a site map provides a general top-down view of the overall site contents.


Benefits of sitemaps

Site maps can improve search engine optimization of a site by making sure that all the pages can be found. This is especially important if a site uses Adobe Flash or JavaScript menus that do not include HTML links.

Most search engines will only follow a finite number of links from a page, so if a site is very large, the site map may be required so that search engines and visitors can access all content on the site.

[edit] XML sitemaps

Google introduced Google Sitemaps so web developers can publish lists of links from across their sites. The basic premise is that some sites have a large number of dynamic pages that are only available through the use of forms and user entries. The sitemap files can then be used to indicate to a web crawler how such pages can be found.
Google, MSN, Yahoo and Ask now jointly support the Sitemaps protocol.

Since MSN, Yahoo, Ask, and Google use the same protocol, having a sitemap lets the four biggest search engines have the updated page information. Sitemaps do not guarantee all links will be crawled, and being crawled does not guarantee indexing. However, a sitemap is still the best insurance for getting a search engine to learn about your entire site.

XML sitemaps have replaced the older method of "submitting to search engines" by filling out a form on the search engine's submission page. Now web developers submit a sitemap directly, or wait for search engines to find it.

Biositemap

The Biositemaps Protocol allows scientists, engineers, centers and institutions engaged in modeling, software tool development and analysis of biomedical and informatics data to broadcast and disseminate to the world the information about their latest computational biology resources (data, software tools and web-services). The biositemap concept is based on ideas from and Crawler-friendly Web Servers, and it integrates the features of Sitemaps and RSS feeds into a decentralized mechanism for announcing and communicating updates to existent and introduction of new biomedical data and computing resources. These site, institution or investigator specific biositemap descriptions are posted in XML format online and are searched, parsed, monitored and interpreted by web search engines, human and machine interfaces, custom-design web crawlers and other outlets interested in discovering updated or novel resources for bioinformatics and biomedical research investigations. The biositemap mechanism separates the providers of biomedical resources (investigators or institutions) from the consumers of resource content (researchers, clinicians, news media, funding agencies, educational and research initiatives).

A Biositemap is an XML file that lists the biomedical and bioinformatics resources for a specific research group or consortium. It allows developers of biomedical resources to completely describe the functionality and usability and of each of their software tools, databases or web-services.



* when providers and consumers of bioinformatics and biomedical computing resources need to communicate in a scalable, efficient, agile and decentralized fashion. In these cases, a human (graphical) or a machine (computer) interface connects the descriptions of resources and facilities the search, comparison and utilization of most relevant resources for specific scientific studies. This infrastructure enables effective and timely matching of services and needs among biomedical investigators and the public in general.
* where meta-resources, computational or digital libraries need to update their contents to reflect the current states of newly developed biomedical materials and resources using AJAX, JSON or WSDL protocols.

Biositemaps supplement and do not replace the existing frameworks for dissemination of data, tools and services. By broadcasting a relevant and up-to-date Biositemap file on the web, investigators and institutions are only helping different engine's crawlers, machine interfaces and users dynamically acquire, interpret, process and utilize the most accurate information about the state of the resources disseminated by the developing group. Using this biositemap protocol does not guarantee that your resources will be included in search indexes nor does it influence the way that your tools are ranked or perceived by the community.

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About Google Guidelines

Here for you around Google guidlines, The Google webmaster guidelines are a list of suggested practices Google has provided as guidance to webmasters. Websites that do not follow some of the guidelines may be removed from the Google index. A website experiencing problems being indexed or ranked well can find direction in the guidelines. Often websites are not following all of the guidelines and may experience a lower ranking in Google's search engine results or complete removal from the Google index. There are currently thirty-one guidelines which are split into four categories:

1. Quality: There are five "basic principles" and eight "specific guidelines" in this category. These guidelines are directed toward deceptive behavior and manipulation attempts that may lessen the quality of the Google search engine results. Violations of the quality guidelines are the most common reason of a website being removed from Google's index.
2. Technical: There are five guidelines in this category. These guidelines cover specific issues that may inhibit a web page from being seen by Googlebot, which is Google's search engine crawler.
3. Design and content: There are nine guidelines in this category. These guidelines give practical information to webmasters concerning the way their site is built and represent the most common unintentional mistakes that webmasters make.
4. When your site is ready:There are five guidelines in this category. These guideline provide specific direction for a webmaster who has created a new site and are also relevant for older sites which are not yet in the Google index.

Let's Blogging !

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Web Design

Web page design is a process of conceptualization, planning, modeling, and execution of electronic media content delivery via Internet in the form of technologies (such as markup languages) suitable for interpretation and display by a web browser or other web-based graphical user interfaces (GUIs).

The intent of web design is to create a web site (a collection of electronic files residing on one or more web servers) that presents content (including interactive features or interfaces) to the end user in the form of web pages once requested. Such elements as text, forms, and bit-mapped images (GIFs, JPEGs, PNGs) can be placed on the page using HTML, XHTML, or XML tags. Displaying more complex media (vector graphics, animations, videos, sounds) usually requires plug-ins such as Flash, QuickTime, Java run-time environment, etc. Plug-ins are also embedded into web pages by using HTML or XHTML tags.

Improvements in the various browsers' compliance with W3C standards prompted a widespread acceptance of XHTML and XML in conjunction with Cascading Style Sheets (CSS) to position and manipulate web page elements. The latest standards and proposals aim at leading to the various browsers' ability to deliver a wide variety of media and accessibility options to the client possibly without employing plug-ins.

Typically web pages are classified as static or dynamic.

* Static pages don’t change content and layout with every request unless a human (web master or programmer) manually updates the page.

* Dynamic pages adapt their content and/or appearance depending on the end-user’s input or interaction or changes in the computing environment (user, time, database modifications, etc.) Content can be changed on the client side (end-user's computer) by using client-side scripting languages (JavaScript, JScript, Actionscript, media players and PDF reader plug-ins, etc.) to alter DOM elements (DHTML). Dynamic content is often compiled on the server utilizing server-side scripting languages (PHP, ASP, Perl, Coldfusion, JSP, Python, etc.). Both approaches are usually used in complex applications.

With growing specialization within communication design and information technology fields, there is a strong tendency to draw a clear line between web design specifically for web pages and web development for the overall logistics of all web-based services.

Web Site Design

A web site is a collection of information about a particular topic or subject. Designing a web site is defined as the arrangement and creation of web pages that in turn make up a web site. A web page consists of information for which the web site is developed. A web site might be compared to a book, where each page of the book is a web page.

There are many aspects (design concerns) in this process, and due to the rapid development of the Internet, new aspects may emerge. For non-commercial web sites, the goals may vary depending on the desired exposure and response. For typical commercial web sites, the basic aspects of design are:

* The content: the substance, and information on the site should be relevant to the site and should target the area of the public that the website is concerned with.
* The usability: the site should be user-friendly, with the interface and navigation simple and reliable.
* The appearance: the graphics and text should include a single style that flows throughout, to show consistency. The style should be professional, appealing and relevant.
* The visibility: the site must also be easy to find via most, if not all, major search engines and advertisement media.

A web site typically consists of text and images. The first page of a web site is known as the Home page or Index. Some web sites use what is commonly called a Splash Page. Splash pages might include a welcome message, language or region selection, or disclaimer. Each web page within a web site is an HTML file which has its own URL. After each web page is created, they are typically linked together using a navigation menu composed of hyperlinks. Faster browsing speeds have led to shorter attention spans and more demanding online visitors and this has resulted in less use of Splash Pages, particularly where commercial web sites are concerned.

Once a web site is completed, it must be published or uploaded in order to be viewable to the public over the internet. This may be done using an FTP client. Once published, the web master may use a variety of techniques to increase the traffic, or hits, that the web site receives. This may include submitting the web site to a search engine such as Google or Yahoo, exchanging links with other web sites, creating affiliations with similar web sites, etc.

Multidisciplinary requirements

Web site design crosses multiple disciplines of information systems, information technology and communication design. The web site is an information system whose components are sometimes classified as front-end and back-end. The observable content (e.g. page layout, user interface, graphics, text, audio) is known as the front-end. The back-end comprises the organization and efficiency of the source code, invisible scripted functions, and the server-side components that process the output from the front-end. Depending on the size of a Web development project, it may be carried out by a multi-skilled individual (sometimes called a web master), or a project manager may oversee collaborative design between group members with specialized skills.

Issues

As in collaborative designs, there are conflicts between differing goals and methods of web site designs. These are a few of the ongoing ones.

Lack of collaboration in design

In the early stages of the web, there wasn't as much collaboration between web designs and larger advertising campaigns, customer transactions, social networking, intranets and extranets as there is now. Web pages were mainly static online brochures disconnected from the larger projects.

Many web pages are still disconnected from larger projects. Special design considerations are necessary for use within these larger projects. These design considerations are often overlooked, especially in cases where there is a lack of leadership, lack of understanding of why and technical knowledge of how to integrate, or lack of concern for the larger project in order to facilitate collaboration. This often results in unhealthy competition or compromise between departments, and less than optimal use of web pages.

Liquid versus fixed layouts

On the web the designer has no control over several factors, including the size of the browser window, the web browser used, the input devices used (mouse, touch screen, voice command, text, cell phone number pad, etc.) and the size and characteristics of available fonts.

Some designers choose to control the appearance of the elements on the screen by using specific width designations. This control may be achieved through the use of a HTML table-based design or a more semantic div-based design through the use of CSS. Whenever the text, images, and layout of a design do not change as the browser changes, this is referred to as a fixed width design. Proponents of fixed width design prefer precise control over the layout of a site and the precision placement of objects on the page. Other designers choose a liquid design. A liquid design is one where the design moves to flow content into the whole screen, or a portion of the screen, no matter what the size of the browser window. Proponents of liquid design prefer greater compatibility and using the screen space available. Liquid design can be achieved through the use of CSS, by avoiding styling the page altogether, or by using HTML tables (or more semantic divs) set to a percentage of the page. Both liquid and fixed design developers must make decisions about how the design should degrade on higher and lower screen resolutions. Sometimes the pragmatic choice is made to flow the design between a minimum and a maximum width. This allows the designer to avoid coding for the browser choices making up The Long Tail, while still using all available screen space. Depending on the purpose of the content, a web designer may decide to use either fixed or liquid layouts on a case-by-case basis.

Similar to liquid layout is the optional fit to window feature with Adobe Flash content. This is a fixed layout that optimally scales the content of the page without changing the arrangement or text wrapping when the browser is resized.

Flash

Adobe Flash (formerly Macromedia Flash) is a proprietary, robust graphics animation or application development program used to create and deliver dynamic content, media (such as sound and video), and interactive applications over the web via the browser.

Flash is not a standard produced by a vendor-neutral standards organization like most of the core protocols and formats on the Internet. Flash is much more restrictive than the open HTML format, though, requiring a proprietary plugin to be seen, and it does not integrate with most web browser UI features like the "Back" button.

According to a study, 98% of US Web users have the Flash Player installed.[3] The percentage has remained fairly constant over the years; for example, a study conducted by NPD Research in 2002 showed that 97.8% of US Web users had the Flash player installed. Numbers vary depending on the detection scheme and research demographics.

Many graphic artists use Flash because it gives them exact control over every part of the design, and anything can be animated and generally "jazzed up". Some application designers enjoy Flash because it lets them create applications that do not have to be refreshed or go to a new web page every time an action occurs. Flash can use embedded fonts instead of the standard fonts installed on most computers. There are many sites which forgo HTML entirely for Flash. Other sites may use Flash content combined with HTML as conservatively as gifs or jpegs would be used, but with smaller vector file sizes and the option of faster loading animations. Flash may also be used to protect content from unauthorized duplication or searching. Alternatively, small, dynamic Flash objects may be used to replace standard HTML elements (such as headers or menu links) with advanced typography not possible via regular HTML or CSS (see Scalable Inman Flash Replacement).

Flash detractors claim that Flash websites tend to be poorly designed, and often use confusing and non-standard user-interfaces, such as the inability to scale according to the size of the web browser, or it's incompatibility with common browser features such as the back button. Up until recently, search engines have been unable to index Flash objects, which has prevented sites from having their contents easily found. This is because many search engine crawlers rely on text to index websites. It is possible to specify alternate content to be displayed for browsers that do not support Flash. Using alternate content also helps search engines to understand the page, and can result in much better visibility for the page. However, the vast majority of Flash websites are not disability accessible (for screen readers, for example) or Section 508 compliant. An additional issue is that sites which commonly use alternate content for search engines to their human visitors are usually judged to be spamming search engines and are automatically banned.

The most recent incarnation of Flash's scripting language (called "ActionScript", which is an ECMA language similar to JavaScript) incorporates long-awaited usability features, such as respecting the browser's font size and allowing blind users to use screen readers. Actionscript 2.0 is an Object-Oriented language, allowing the use of CSS, XML, and the design of class-based web applications.

CSS versus tables for layout



When Netscape Navigator 4 dominated the browser market, the popular solution available for designers to lay out a Web page was by using tables. Often even simple designs for a page would require dozens of tables nested in each other. Many web templates in Dreamweaver and other WYSIWYG editors still use this technique today. Navigator 4 didn't support CSS to a useful degree, so it simply wasn't used.

After the browser wars subsided, and the dominant browsers such as Internet Explorer became more W3C compliant, designers started turning toward CSS as an alternate means of laying out their pages. CSS proponents say that tables should be used only for tabular data, not for layout. Using CSS instead of tables also returns HTML to a semantic markup, which helps bots and search engines understand what's going on in a web page. All modern Web browsers support CSS with different degrees of limitations.

However, one of the main points against CSS is that by relying on it exclusively, control is essentially relinquished as each browser has its own quirks which result in a slightly different page display. This is especially a problem as not every browser supports the same subset of CSS rules. For designers who are used to table-based layouts, developing Web sites in CSS often becomes a matter of trying to replicate what can be done with tables, leading some to find CSS design rather cumbersome due to lack of familiarity. For example, at one time it was rather difficult to produce certain design elements, such as vertical positioning, and full-length footers in a design using absolute positions. With the abundance of CSS resources available online today, though, designing with reasonable adherence to ,;;' standards involves little more than applying CSS 2.1 or CSS 3 to properly structured markup.

These days most modern browsers have solved most of these quirks in CSS rendering and this has made many different CSS layouts possible. However, some people continue to use old browsers, and designers need to keep this in mind, and allow for graceful degrading of pages in older browsers. Most notable among these old browsers are Internet Explorer 5 and 5.5, which, according to some web designers, are becoming the new Netscape Navigator 4 — a block that holds the World Wide Web back from converting to CSS design. However, the W3 Consortium has made CSS in combination with XHTML the standard for web design.

Form versus Function

Some web developers have a graphic arts background and may pay more attention to how a page looks than considering other issues such as how visitors are going to find the page via a search engine. Some might rely more on advertising than search engines to attract visitors to the site. On the other side of the issue, search engine optimization consultants (SEOs) are concerned with how well a web site works technically and textually: how much traffic it generates via search engines, and how many sales it makes, assuming looks don't contribute to the sales. As a result, the designers and SEOs often end up in disputes where the designer wants more 'pretty' graphics, and the SEO wants lots of 'ugly' keyword-rich text, bullet lists, and text links. One could argue that this is a false dichotomy due to the possibility that a web design may integrate the two disciplines for a collaborative and synergistic solution. Because some graphics serve communication purposes in addition to aesthetics, how well a site works may depend on the graphic designer's visual communication ideas as well as the SEO considerations.

Another problem when using a lot of graphics on a page is that download times can be greatly lengthened, often irritating the user. This has become less of a problem as the internet has evolved with high-speed internet and the use of vector graphics. This is an engineering challenge to increase bandwidth in addition to an artistic challenge to minimize graphics and graphic file sizes. This is an on-going challenge as increased bandwidth invites increased amounts of content.

Accessible Web design

Web accessibility

To be accessible, web pages and sites must conform to certain accessibility principles. These can be grouped into the following main areas:

* use semantic markup that provides a meaningful structure to the document (i.e. web page)
* Semantic markup also refers to semantically organizing the web page structure and publishing web services description accordingly so that they can be recognized by other web services on different web pages. Standards for semantic web are set by IEEE
* use a valid markup language that conforms to a published DTD or Schema
* provide text equivalents for any non-text components (e.g. images, multimedia)
* use hyperlinks that make sense when read out of context. (e.g. avoid "Click Here.")
* don't use frames
* use CSS rather than HTML Tables for layout.
* author the page so that when the source code is read line-by-line by user agents (such as a screen readers) it remains intelligible. (Using tables for design will often result in information that is not.)

However, W3C permits an exception where tables for layout either make sense when linearized or an alternate version (perhaps linearized) is made available.

Website accessibility is also changing as it is impacted by Content Management Systems that allow changes to be made to webpages without the need of obtaining programming language knowledge.

Website Planning

Before creating and uploading a website, it is important to take the time to plan exactly what is needed in the website. Thoroughly considering the audience or target market, as well as defining the purpose and deciding what content will be developed are extremely important.

Purpose

It is essential to define the purpose of the website as one of the first steps in the planning process. A purpose statement should show focus based on what the website will accomplish and what the users will get from it. A clearly defined purpose will help the rest of the planning process as the audience is identified and the content of the site is developed. Setting short and long term goals for the website will help make the purpose clear and plan for the future when expansion, modification, and improvement will take place. Also, goal-setting practices and measurable objectives should be identified to track the progress of the site and determine success.

Audience

Defining the audience is a key step in the website planning process. The audience is the group of people who are expected to visit your website – the market being targeted. These people will be viewing the website for a specific reason and it is important to know exactly what they are looking for when they visit the site. A clearly defined purpose or goal of the site as well as an understanding of what visitors want to do or feel when they come to your site will help to identify the target audience. Upon considering who is most likely to need or use the content, a list of characteristics common to the users such as:

* Audience Characteristics
* Information Preferences
* Computer Specifications
* Web Experience

Taking into account the characteristics of the audience will allow an effective website to be created that will deliver the desired content to the target audience.

Content

Content evaluation and organization requires that the purpose of the website be clearly defined. Collecting a list of the necessary content then organizing it according to the audience's needs is a key step in website planning. In the process of gathering the content being offered, any items that do not support the defined purpose or accomplish target audience objectives should be removed. It is a good idea to test the content and purpose on a focus group and compare the offerings to the audience needs. The next step is to organize the basic information structure by categorizing the content and organizing it according to user needs. Each category should be named with a concise and descriptive title that will become a link on the website. Planning for the site's content ensures that the wants or needs of the target audience and the purpose of the site will be fulfilled.

Compatibility and restrictions

Because of the market share of modern browsers (depending on your target market), the compatibility of your website with the viewers is restricted. For instance, a website that is designed for the majority of websurfers will be limited to the use of valid XHTML 1.0 Strict or older, Cascading Style Sheets Level 1, and 1024x768 display resolution. This is because Internet Explorer is not fully W3C standards compliant with the modularity of XHTML 1.1 and the majority of CSS beyond 1. A target market of more alternative browser (e.g. Firefox and Opera) users allow for more W3C compliance and thus a greater range of options for a web designer.

Another restriction on webpage design is the use of different Image file formats. The majority of users can support GIF, JPEG, and PNG (with restrictions). Again Internet Explorer is the major restriction here, not fully supporting PNG's advanced transparency features, resulting in the GIF format still being the most widely used graphic file format for transparent images.

Many website incompatibilities go unnoticed by the designer and unreported by the users. The only way to be certain a website will work on a particular platform is to test it on that platform.

Planning Documentation

Documentation is used to visually plan the site while taking into account the purpose, audience and content, to design the site structure, content and interactions that are most suitable for the website. Documentation may be considered a prototype for the website – a model which allows the website layout to be reviewed, resulting in suggested changes, improvements and/or enhancements. This review process increases the likelihood of success of the website.

First, the content is categorized and the information structure is formulated. The information structure is used to develop a document or visual diagram called a site map. This creates a visual of how the web pages will be interconnected, which helps in deciding what content will be placed on what pages. There are three main ways of diagramming the website structure:

* Linear Website Diagrams will allow the users to move in a predetermined sequence;
* Hierarchical structures (of Tree Design Website Diagrams) provide more than one path for users to take to their destination;
* Branch Design Website Diagrams allow for many interconnections between web pages such as hyperlinks within sentences.

In addition to planning the structure, the layout and interface of individual pages may be planned using a storyboard. In the process of storyboarding, a record is made of the description, purpose and title of each page in the site, and they are linked together according to the most effective and logical diagram type. Depending on the number of pages required for the website, documentation methods may include using pieces of paper and drawing lines to connect them, or creating the storyboard using computer software.

Some or all of the individual pages may be designed in greater detail as a website wireframe, a mock up model or comprehensive layout of what the page will actually look like. This is often done in a graphic program, or layout design program. The wireframe has no working functionality, only planning, though it can be used for selling ideas to other web design companies.

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Domain Name System

The Domain Name System (DNS) is a hierarchical naming system for computers, services, or any resource participating in the Internet. It associates various information with domain names assigned to such participants. Most importantly, it translates humanly meaningful domain names to the numerical (binary) identifiers associated with networking equipment for the purpose of locating and addressing these devices world-wide. An often used analogy to explain the Domain Name System is that it serves as the "phone book" for the Internet by translating human-friendly computer hostnames into IP addresses. For example, www.example.com translates to 208.77.188.166.

he Domain Name System makes it possible to assign domain names to groups of Internet users in a meaningful way, independent of each user's physical location. Because of this, World-Wide Web (WWW) hyperlinks and Internet contact information can remain consistent and constant even if the current Internet routing arrangements change or the participant uses a mobile device. Internet domain names are easier to remember than IP addresses such as 208.77.188.166(IPv4) or 2001:db8:1f70::999:de8:7648:6e8 (IPv6). People take advantage of this when they recite meaningful URLs and e-mail addresses without having to know how the machine will actually locate them.

The Domain Name System distributes the responsibility for assigning domain names and mapping them to Internet Protocol (IP) networks by designating authoritative name servers for each domain to keep track of their own changes, avoiding the need for a central register to be continually consulted and updated.

In general, the Domain Name System also stores other types of information, such as the list of mail servers that accept email for a given Internet domain. By providing a world-wide, distributed keyword-based redirection service, the Domain Name System is an essential component of the functionality of the Internet.

Other identifiers such as RFID tags, UPC codes, International characters in email addresses and host names, and a variety of other identifiers could all potentially utilize DNS .

The Domain Name System also defines the technical underpinnings of the functionality of this database service. For this purpose it defines the DNS protocol, a detailed specification of the data structures and communication exchanges used in DNS, as part of the Internet Protocol Suite (TCP/IP). The context of the DNS within the Internet protocols may be seen in the following diagram. The DNS protocol was developed and defined in the early 1980's and published by the Internet Engineering Task Force (cf. History).

History

The practice of using a name as a more human-legible abstraction of a machine's numerical address on the network predates even TCP/IP. This practice dates back to the ARPAnet era. Back then, a different system was used. The DNS was invented in 1983, shortly after TCP/IP was deployed. With the older system, each computer on the network retrieved a file called HOSTS.TXT from a computer at SRI (now SRI International). The HOSTS.TXT file mapped numerical addresses to names. A hosts file still exists on most modern operating systems, either by default or through configuration, and allows users to specify an IP address (eg. 208.77.188.166) to use for a hostname (eg. www.example.net) without checking DNS. Systems based on a hosts file have inherent limitations, because of the obvious requirement that every time a given computer's address changed, every computer that seeks to communicate with it would need an update to its hosts file.

The growth of networking required a more scalable system that recorded a change in a host's address in one place only. Other hosts would learn about the change dynamically through a notification system, thus completing a globally accessible network of all hosts' names and their associated IP Addresses.

At the request of Jon Postel, Paul Mockapetris invented the Domain Name system in 1983 and wrote the first implementation. The original specifications appear in RFC 882 and RFC 883. In November 1987, the publication of RFC 1034 and RFC 1035 updated the DNS specification and made RFC 882 and RFC 883 obsolete. Several more-recent RFCs have proposed various extensions to the core DNS protocols.

In 1984, four Berkeley students—Douglas Terry, Mark Painter, David Riggle and Songnian Zhou—wrote the first UNIX implementation, which was maintained by Ralph Campbell thereafter. In 1985, Kevin Dunlap of DEC significantly re-wrote the DNS implementation and renamed it BIND—Berkeley Internet Name Domain. Mike Karels, Phil Almquist and Paul Vixie have maintained BIND since then. BIND was ported to the Windows NT platform in the early 1990s.

BIND was widely distributed, especially on Unix systems, and is the dominant DNS software in use on the Internet. With the heavy use and resulting scrutiny of its open-source code, as well as increasingly more sophisticated attack methods, many security flaws were discovered in BIND. This contributed to the development of a number alternative nameserver and resolver programs. BIND itself was re-written from scratch in version 9, which has a security record comparable to other modern Internet software.

Structure

The domain name space
Domain names, arranged in a tree, cut into zones, each served by a nameserver.

The domain name space consists of a tree of domain names. Only one node or leaf in the tree has zero or more resource records, which hold information associated with the domain name. The tree sub-divides into zones beginning at the root zone. A DNS zone consists of a collection of connected nodes authoritatively served by an authoritative nameserver. (Note that a single nameserver can host several zones.)

Administrative responsibility over any zone may be divided, thereby creating additional zones. Authority is said to be delegated for a portion of the old space, usually in form of sub-domains, to another nameserver and administrative entity. The old zone ceases to be authoritative for the new zone.

Parts of a domain name

A domain name usually consists of two or more parts (technically a label), which is conventionally written separated by dots, such as example.com.

* The rightmost label conveys the top-level domain (for example, the address www.example.com has the top-level domain com).
* Each label to the left specifies a subdivision, or subdomain of the domain above it. Note: “subdomain” expresses relative dependence, not absolute dependence. For example: example.com is a subdomain of the com domain, and www.example.com is a subdomain of the domain example.com. In theory, this subdivision can go down 127 levels. Each label can contain up to 63 octets. The whole domain name may not exceed a total length of 253 octets. In practice, some domain registries may have shorter limits.
* A hostname refers to a domain name that has one or more associated IP addresses; ie: the 'www.example.com' and 'example.com' domains are both hostnames, however, the 'com' domain is not.

DNS servers

Name server

The Domain Name System is maintained by a distributed database system, which uses the client-server model. The nodes of this database are the name servers. Each domain or subdomain has one or more authoritative DNS servers that publish information about that domain and the name servers of any domains subordinate to it. The top of the hierarchy is served by the root nameservers: the servers to query when looking up (resolving) a top-level domain name (TLD).

DNS resolvers


The client-side of the DNS is called a DNS resolver. It is responsible for initiating and sequencing the queries that ultimately lead to a full resolution (translation) of the resource sought, e.g., translation of a domain name into an IP address.

A DNS query may be either a recursive query or a non-recursive query:

* A non-recursive query is one in which the DNS server may provide a partial answer to the query (or give an error).
* A recursive query is one where the DNS server will fully answer the query (or give an error). DNS servers are not required to support recursive queries.

The resolver (or another DNS server acting recursively on behalf of the resolver) negotiates use of recursive service using bits in the query headers.

Resolving usually entails iterating through several name servers to find the needed information. However, some resolvers function simplistically and can communicate only with a single name server. These simple resolvers rely on a recursive query to a recursive name server to perform the work of finding information for them.


Address resolution mechanism

In theory a full host name may have several name segments, (e.g ahost.ofasubnet.ofabiggernet.inadomain.example). In practice, full host names will frequently consist of just three segments (ahost.inadomain.example, and most often www.inadomain.example). For querying purposes, software interprets the name segment by segment, from right to left, using an iterative search procedure. At each step along the way, the program queries a corresponding DNS server to provide a pointer to the next server which it should consult.
A DNS recursor consults three nameservers to resolve the address www.wikipedia.org.

As originally envisaged, the process was as simple as:

1. the local system is pre-configured with the known addresses of the root servers in a file of root hints, which need to be updated periodically by the local administrator from a reliable source to be kept up to date with the changes which occur over time.
2. query one of the root servers to find the server authoritative for the next level down (so in the case of our simple hostname, a root server would be asked for the address of a server with detailed knowledge of the example top level domain).
3. querying this second server for the address of a DNS server with detailed knowledge of the second-level domain (inadomain.example in our example).
4. repeating the previous step to progress down the name, until the final step which would, rather than generating the address of the next DNS server, return the final address sought.

The diagram illustrates this process for the real host www.wikipedia.org.

The mechanism in this simple form has a difficulty: it places a huge operating burden on the root servers, with every search for an address starting by querying one of them. Being as critical as they are to the overall function of the system, such heavy use would create an insurmountable bottleneck for trillions of queries placed every day. In practice caching is used to overcome this problem, and in actual fact root nameservers deal with very little of the total traffic.

Circular dependencies and glue records

Name servers in delegations appear listed by name, rather than by IP address. This means that a resolving name server must issue another DNS request to find out the IP address of the server to which it has been referred. Since this can introduce a circular dependency if the nameserver referred to is under the domain that it is authoritative of, it is occasionally necessary for the nameserver providing the delegation to also provide the IP address of the next nameserver. This record is called a glue record.

For example, assume that the sub-domain en.wikipedia.org contains further sub-domains (such as something.en.wikipedia.org) and that the authoritative name server for these lives at ns1.something.en.wikipedia.org. A computer trying to resolve something.en.wikipedia.org will thus first have to resolve ns1.something.en.wikipedia.org. Since ns1 is also under the something.en.wikipedia.org subdomain, resolving ns1.something.en.wikipedia.org requires resolving something.en.wikipedia.org which is exactly the circular dependency mentioned above. The dependency is broken by the glue record in the nameserver of en.wikipedia.org that provides the IP address of ns1.something.en.wikipedia.org directly to the requestor, enabling it to bootstrap the process by figuring out where ns1.something.en.wikipedia.org is located.

In practice

When an application (such as a web browser) tries to find the IP address of a domain name, it doesn't necessarily follow all of the steps outlined in the Theory section above. We will first look at the concept of caching, and then outline the operation of DNS in "the real world."

Caching and time to live

Because of the huge volume of requests generated by a system like DNS, the designers wished to provide a mechanism to reduce the load on individual DNS servers. To this end, the DNS resolution process allows for caching (i.e. the local recording and subsequent consultation of the results of a DNS query) for a given period of time after a successful answer. How long a resolver caches a DNS response (i.e. how long a DNS response remains valid) is determined by a value called the time to live (TTL). The TTL is set by the administrator of the DNS server handing out the response. The period of validity may vary from just seconds to days or even weeks.

Caching time

As a noteworthy consequence of this distributed and caching architecture, changes to DNS do not always take effect immediately and globally. This is best explained with an example: If an administrator has set a TTL of 6 hours for the host www.wikipedia.org, and then changes the IP address to which www.wikipedia.org resolves at 12:01pm, the administrator must consider that a person who cached a response with the old IP address at 12:00noon will not consult the DNS server again until 6:00pm. The period between 12:01pm and 6:00pm in this example is called caching time, which is best defined as a period of time that begins when you make a change to a DNS record and ends after the maximum amount of time specified by the TTL expires. This essentially leads to an important logistical consideration when making changes to DNS: not everyone is necessarily seeing the same thing you're seeing. RFC 1537 helps to convey basic rules for how to set the TTL.

Note that the term "propagation", although very widely used in this context, does not describe the effects of caching well. Specifically, it implies that when you make a DNS change, it somehow spreads to all other DNS servers (instead, other DNS servers check in with yours as needed), and that you do not have control over the amount of time the record is cached (you control the TTL values for all DNS records in your domain, except your NS records and any authoritative DNS servers that use your domain name).

Some resolvers may override TTL values, as the protocol supports caching for up to 68 years or no caching at all. Negative caching (the non-existence of records) is determined by name servers authoritative for a zone which MUST include the Start of Authority (SOA) record when reporting no data of the requested type exists. The MINIMUM field of the SOA record and the TTL of the SOA itself is used to establish the TTL for the negative answer. RFC 2308

Many people incorrectly refer to a mysterious 48 hour or 72 hour propagation time when you make a DNS change. When one changes the NS records for one's domain or the IP addresses for hostnames of authoritative DNS servers using one's domain (if any), there can be a lengthy period of time before all DNS servers use the new information. This is because those records are handled by the zone parent DNS servers (for example, the .com DNS servers if your domain is example.com), which typically cache those records for 48 hours. However, those DNS changes will be immediately available for any DNS servers that do not have them cached. And any DNS changes on your domain other than the NS records and authoritative DNS server names can be nearly instantaneous, if you choose for them to be (by lowering the TTL once or twice ahead of time, and waiting until the old TTL expires before making the change).

In the real world
DNS resolving from program to OS-resolver to ISP-resolver to greater system.

Users generally do not communicate directly with a DNS resolver. Instead DNS-resolution takes place transparently in client-applications such as web-browsers, mail-clients, and other Internet applications. When an application makes a request which requires a DNS lookup, such programs send a resolution request to the local DNS resolver in the local operating system, which in turn handles the communications required.

The DNS resolver will almost invariably have a cache (see above) containing recent lookups. If the cache can provide the answer to the request, the resolver will return the value in the cache to the program that made the request. If the cache does not contain the answer, the resolver will send the request to one or more designated DNS servers. In the case of most home users, the Internet service provider to which the machine connects will usually supply this DNS server: such a user will either have configured that server's address manually or allowed DHCP to set it; however, where systems administrators have configured systems to use their own DNS servers, their DNS resolvers point to separately maintained nameservers of the organization. In any event, the name server thus queried will follow the process outlined above, until it either successfully finds a result or does not. It then returns its results to the DNS resolver; assuming it has found a result, the resolver duly caches that result for future use, and hands the result back to the software which initiated the request.

Broken resolvers

An additional level of complexity emerges when resolvers violate the rules of the DNS protocol. A number of large ISPs have configured their DNS servers to violate rules (presumably to allow them to run on less-expensive hardware than a fully-compliant resolver), such as by disobeying TTLs, or by indicating that a domain name does not exist just because one of its name servers does not respond.[citation needed]

As a final level of complexity, some applications (such as web-browsers) also have their own DNS cache, in order to reduce the use of the DNS resolver library itself. This practice can add extra difficulty when debugging DNS issues, as it obscures the freshness of data, and/or what data comes from which cache. These caches typically use very short caching times — on the order of one minute. Internet Explorer offers a notable exception: recent versions cache DNS records for half an hour.

Other applications

The system outlined above provides a somewhat simplified scenario. The Domain Name System includes several other functions:

* Hostnames and IP addresses do not necessarily match on a one-to-one basis. Many hostnames may correspond to a single IP address: combined with virtual hosting, this allows a single machine to serve many web sites. Alternatively a single hostname may correspond to many IP addresses: this can facilitate fault tolerance and load distribution, and also allows a site to move physical location seamlessly.
* There are many uses of DNS besides translating names to IP addresses. For instance, Mail transfer agents use DNS to find out where to deliver e-mail for a particular address. The domain to mail exchanger mapping provided by MX records accommodates another layer of fault tolerance and load distribution on top of the name to IP address mapping.
* Sender Policy Framework and DomainKeys, instead of creating their own record types, were designed to take advantage of another DNS record type, the TXT record.
* To provide resilience in the event of computer failure, multiple DNS servers are usually provided for coverage of each domain, and at the top level, thirteen very powerful root servers exist, with additional "copies" of several of them distributed worldwide via Anycast.

Protocol details

DNS primarily uses UDP on port 53 to serve requests. Almost all DNS queries consist of a single UDP request from the client followed by a single UDP reply from the server. TCP comes into play only when the response data size exceeds 512 bytes, or for such tasks as zone transfer. Some operating systems such as HP-UX are known to have resolver implementations that use TCP for all queries, even when UDP would suffice.

Extensions to DNS

EDNS is an extension of the DNS protocol which allows the transport over UDP of DNS replies exceeding 512 bytes, and adds support for expanding the space of request and response codes. It is described in RFC 2671.

Types of DNS records

List of DNS record types

When sent over the Internet, all records use the common format specified in RFC 1035 shown below.
RR (Resource record) fields Field Description Length (octets)
NAME Name of the node to which this record pertains. (variable)
TYPE Type of RR. For example, MX is type 15. 2
CLASS Class code. 2
TTL Signed time in seconds that RR stays valid. 4
RDLENGTH Length of RDATA field. 2
RDATA Additional RR-specific data. (variable)

The type of the record indicates what the format of the data is, and gives a hint of its intended use; for instance, the A record is used to translate from a domain name to an IPv4 address, the NS record lists which name servers can answer lookups on a DNS zone, and the MX record is used to translate from a name in the right-hand side of an e-mail address to the name of a machine able to handle mail for that address.

Many more record types exist and be found in the complete List of DNS record types.

Internationalized domain names

Internationalized domain name

While domain names technically have no restrictions on the characters they use and can include non-ASCII characters, the same is not true for host names.[8] Host names are the names most people see and use for things like e-mail and web browsing. Host names are restricted to a small subset of the ASCII character set known as LDH, the Letters A–Z in upper and lower case, Digits 0–9, Hyphen, and the dot to separate LDH-labels; see RFC 3696 section 2 for details. This prevented the representation of names and words of many languages natively. ICANN has approved the Punycode-based IDNA system, which maps Unicode strings into the valid DNS character set, as a workaround to this issue. Some registries have adopted IDNA.

Security issues

DNS was not originally designed with security in mind, and thus has a number of security issues.

One class of vulnerabilities is DNS cache poisoning, which tricks a DNS server into believing it has received authentic information when, in reality, it has not.

DNS responses are traditionally not cryptographically signed, leading to many attack possibilities; DNSSEC modifies DNS to add support for cryptographically signed responses. There are various extensions to support securing zone transfer information as well.

Even with encryption, a DNS server could become compromised by a virus (or for that matter a disgruntled employee) that would cause IP addresses of that server to be redirected to a malicious address with a long TTL. This could have far-reaching impact to potentially millions of Internet users if busy DNS servers cache the bad IP data. This would require manual purging of all affected DNS caches as required by the long TTL (up to 68 years).

Some domain names can spoof other, similar-looking domain names. For example, "paypal.com" and "paypa1.com" are different names, yet users may be unable to tell the difference when the user's typeface (font) does not clearly differentiate the letter l and the number 1. This problem is much more serious in systems that support internationalized domain names, since many characters that are different, from the point of view of ISO 10646, appear identical on typical computer screens. This vulnerability is often exploited in phishing.

Techniques such as Forward Confirmed reverse DNS can also be used to help validate DNS results.

Domain Registration

The right to use a domain name is delegated by domain name registrars which are accredited by the Internet Corporation for Assigned Names and Numbers (ICANN), the organization charged with overseeing the name and number systems of the Internet. In addition to ICANN, each top-level domain (TLD) is maintained and serviced technically by a sponsoring organization, the TLD Registry. The registry is responsible for maintaining the database of names registered within the TLDs they administer. The registry receives registration information from each domain name registrar authorized to assign names in the corresponding TLD and publishes the information using a special service, the whois protocol.

Registrars usually charge an annual fee for the service of delegating a domain name to a user and providing a default set of name servers. Often this transaction is termed a sale or lease of the domain name, and the registrant is called an "owner", but no such legal relationship is actually associated with the transaction, only the exclusive right to use the domain name. More correctly authorized users are known as "registrants" or as "domain holders".

ICANN publishes a complete list of TLD registries and domain name registrars in the world. One can obtain information about the registrant of a domain name by looking in the WHOIS database held by many domain registries.

For most of the more than 240 country code top-level domains (ccTLDs), the domain registries hold the authoritative WHOIS (Registrant, name servers, expiration dates, etc.). For instance, DENIC, Germany NIC, holds the authoritative WHOIS to a .DE domain name. Since about 2001, most gTLD registries (.ORG, .BIZ, .INFO) have adopted this so-called "thick" registry approach, i.e. keeping the authoritative WHOIS in the central registries instead of the registrars.

For .COM and .NET domain names, a "thin" registry is used: the domain registry (e.g. VeriSign) holds a basic WHOIS (registrar and name servers, etc.). One can find the detailed WHOIS (registrant, name servers, expiry dates, etc.) at the registrars.

Some domain name registries, also called Network Information Centres (NIC), also function as registrars, and deal directly with end users. But most of the main ones, such as for .COM, .NET, .ORG, .INFO, etc., use a registry-registrar model. There are hundreds of Domain Name Registrars that actually perform the domain name registration with the end user (see lists at ICANN or VeriSign). By using this method of distribution, the registry only has to manage the relationship with the registrar, and the registrar maintains the relationship with the end users, or 'registrants' -- in some cases through additional layers of resellers.

In the process of registering a domain name and maintaining authority over the new name space created, registrars store and use several key pieces of information connected with a domain:

* Administrative contact. A registrant usually designates an administrative contact to manage the domain name. The administrative contact usually has the highest level of control over a domain. Management functions delegated to the administrative contacts may include management of all business information, such as name of record, postal address, and contact information of the official registrant of the domain and the obligation to conform to the requirements of the domain registry in order to retain the right to use a domain name. Furthermore the administrative contact installs additional contact information for technical and billing functions.
* Technical contact. The technical contact manages the name servers of a domain name. The functions of a technical contact include assuring conformance of the configurations of the domain name with the requirements of the domain registry, maintaining the domain zone records, and providing continuous functionality of the name servers (that leads to the accessibility of the domain name).
* Billing contact. The party responsible for receiving billing invoices from the domain name registrar and paying applicable fees.
* Name servers. Domains usually need at least two authoritative name servers that perform name resolution for the domain. If they are not automatically provided by the registrar, the domain holder must specify domain names and IP addresses for these servers.

Abuse and Regulation

Critics often claim abuse of administrative power over domain names. Particularly noteworthy was the VeriSign Site Finder system which redirected all unregistered .com and .net domains to a VeriSign webpage. For example, at a public meeting with VeriSign to air technical concerns about SiteFinder [9], numerous people, active in the IETF and other technical bodies, explained how they were surprised by VeriSign's changing the fundamental behavior of a major component of Internet infrastructure, not having obtained the customary consensus. SiteFinder, at first, assumed every Internet query was for a website, and it monetized queries for incorrect domain names, taking the user to VeriSign's search site. Unfortunately, other applications, such as many implementations of email, treat a lack of response to a domain name query as an indication that the domain does not exist, and that the message can be treated as undeliverable. The original VeriSign implementation broke this assumption for mail, because it would always resolve an erroneous domain name to that of SiteFinder. While VeriSign later changed SiteFinder's behaviour with regard to email, there was still widespread protest about VeriSign's action being more in its financial interest than in the interest of the Internet infrastructure component for which VeriSign was the steward.

Despite widespread criticism, VeriSign only reluctantly removed it after the Internet Corporation for Assigned Names and Numbers (ICANN) threatened to revoke its contract to administer the root name servers. ICANN published the extensive set of letters exchanged, committee reports, and ICANN decisions .

There is also significant disquiet regarding the United States' political influence over ICANN. This was a significant issue in the attempt to create a .xxx top-level domain and sparked greater interest in alternative DNS roots that would be beyond the control of any single country.

Additionally, there are numerous accusations of domain name "front running", whereby registrars, when given whois queries, automatically register the domain name for themselves. Recently, Network Solutions has been accused of this.

Truth in Domain Names Act

Anticybersquatting Consumer Protection Act

In the United States, the "Truth in Domain Names Act" (actually the "Anticybersquatting Consumer Protection Act"), in combination with the PROTECT Act, forbids the use of a misleading domain name with the intention of attracting people into viewing a visual depiction of sexually explicit conduct on the Internet.

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