Tableless web design (or tableless web layout) is a method of web design and development without using HTML tables for page layout control purposes.[1] Instead of HTML tables, style sheet languages such as CSS (Cascading Style Sheets) are used to arrange elements and text on a web page. CSS was introduced by the World Wide Web Consortium (W3C) to improve web accessibility and to make HTML code semantic rather than presentational.

Early in its advent, many web developers considered CSS a more powerful and easier to use way of formatting, and considered the <FONT> tag obsolete. On the other hand early CSS had very limited and difficult to use layout capabilities and many common page layouts (like the 3-column design) that were very easy to implement with tables had no obvious equivalents in CSS.

As of 2006, CSS layout capabilities improved considerably. Many websites still use CSS for text formatting only, while using tables for layout.

Advantages

Accessibility
Because of the Internet’s rapid growth, disability discrimination legislation, and the increasing use of mobile phones and PDAs, it is necessary for Web content to be made accessible to users operating a wide variety of devices. Tableless Web design considerably improves Web accessibility in this respect. Screen readers and braille devices have fewer problems with tableless designs because they follow a logical structure.

As a result of the separation of design (CSS) and structure (HTML), it is also possible to provide different layouts for different devices, e.g. handhelds, mobile phones, etc. It is also possible to specify a different style sheet for print, e.g. to hide or modify the appearance of advertisements or navigation elements that are irrelevant and a nuisance in the printable version of the page.

The W3C’s Web Content Accessibility Guidelines’ guideline no. 3 states “use markup and style sheets and do so properly.”[1] The guideline’s checkpoint 3.3, a priority-2 checkpoint, says “use style sheets to control layout and presentation.”[2]

Bandwidth savings
Clever implementation of tableless design can produce web pages with fewer HTML tags thus reducing page download times. Using external style sheets to position page elements means more mark up language may be cached and further reduce download times for subsequent pages using the same resources.

Poor implementation of tableless design can result in many more lines of code used per page element which can increase download time. Tables have a defined set of rules which are clear and concise while tableless design often involves working around browser inconsistencies.

There is no correlation between tableless design and bandwidth savings. If implemented correctly, the bandwidth savings are generally minor at best. The use of WYSIYG editors or perhaps the competency of the web page’s author has a much greater influence on page download times. It is perfectly possible to build a web page with tables that is lightweight.

Maintainability
Maintaining a website may require frequent changes, both small and large, to the visual style of a website, depending on the purpose of the site. Under table-based layout, the layout is part of the HTML itself. As such, without the aid of template-based visual editors such as HTML editors, changing the positional layout of elements on a whole site may require a great deal of effort, depending on the amount of repetitive changes required. Even employing sed or similar global find-and-replace utilities cannot alleviate the problem entirely.

In tableless layout using CSS, virtually all of the layout information resides in one place: the CSS document. Because the layout information is centralized, these changes can be made quickly and globally by default. The HTML files themselves do not, usually, need to be adjusted when making layout changes. If they do, it is usually to add class-tags to specific markup elements or to change the grouping of various sections with respect to one another.

Also, because the layout information is stored externally to the HTML, it is quite easy to add new content in a tableless design, whether modifying an existing page or adding a new page. By contrast, without such a design, the layout for each page may require a more time-consuming manual changing of each instance or use of global find-and-replace utilities. However site owners often want particular pages to be different from others on the site either for a short period or long term. This will often necessitate a separate style sheet to be developed for that page.

Due to browser inconsistency and a particular web designer’s implementation of tableless design, it may not be clear at first glance exactly how a tableless web page is constructed. While it is convenient to have markup language residing in a single CSS file, it can split layout logic unnecessarily. Browser inconsistencies can increase the risk of web pages failing to render properly which increases the need for maintainability.

Problems
The main problem with tableless design is the wide differences that are to be found in browser support. There are considerable differences in implementing a CSS layout for multiple browsers due to bugs and mis-interpretation of the standards by different browser developers. These necessitate a large number of complex hacks and workarounds in the CSS files, and Web pages need to be tested much more carefully on a wider variety of devices than with table-based design, as some of these bugs can render the content illegible on some browsers.

In addition, CSS support in some older browsers such as Netscape 4 is very incomplete, which can cause major problems if these browsers also need to be targeted.

Conversion to tableless web design has been slow also because of table to layer/css conversion software. HTML editors such as Adobe Dreamweaver can convert tables to layers back and forth. Though this would ease the conversion a little, complications exist in the exactness of the conversion. The centering of tables centers them on the page, but the centering of layers together on different screen resolutions requires some tinkering.

Just as different browsers may interpret tableless design differently, different web designers implement tableless design with varying methods and degrees of skill. As a result, it can sometimes be difficult to read tableless code as compared to a web page with good use of tables which follow a well defined set of rules.
If a web designer has positioned block elements on a web page using the “float” attribute it isn’t always clear how these elements are positioned and what parts of the related CSS file should be edited if adjustments are needed. Adjustments are often needed to widths of block elements in tableless design as browser support is not yet reliable.

Positioning an element on a web page using the “float” attribute encourages the browser to render many pages unintelligible if an error occurs because “float” gives the browser permission to reorganise the web pages by pushing page elements downwards rather than making user friendly adjustments.

There are clear benefits to removing or reducing the use of excess tables on web pages but as a consequence, many web designers are avoiding the use of tables completely. While tables are frowned at in the web design community, they are often the best tool for certain layouts. Often tableless design can offer no benefit at all but require many extra hours of work during website production and maintenance.

Source from- http://en.wikipedia.org/