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Semantic HTML

There is no official specification called "semantic HTML", though the strict flavors of HTML discussed below are a push in that direction. Rather, semantic HTML refers to an objective and a practice to create documents with HTML that contain only the author's intended meaning, without any reference to how this meaning is presented or conveyed. A classic example is the distinction between the emphasis element ( <em> ) and the italics element ( <i> ). Often the emphasis element is displayed in italics, so the presentation is typically the same. However, emphasizing something is different from listing the title of a book, for example, which may also be displayed in italics. In purely semantic HTML, a book title would use a separate element than emphasized text uses (for example a <span> ), because they are each meaningfully different things.

The goal of semantic HTML requires two things of authors:

1. to avoid the use of presentational markup (elements, attributes and other entities)
2. the use of available markup to differentiate the meanings of phrases and structure in the document. So for example, the book title from above would need to have its own element and class specified such as <cite class="booktitle">The Grapes of Wrath</cite>. Here, the <cite> element is used, because it most closely matches the meaning of this phrase in the text. However, the <cite> element is not specific enough to this task because we mean to cite specifically a book title as opposed to a newspaper article or a particular academic journal.

semantic HTML also requires complementary specifications and software compliance with these specifications. Primarily, the development and proliferation of CSS has led to increasing support for semantic HTML because CSS provides designers with a rich language to alter the presentation of semantic-only documents. With the development of CSS the need to include presentational properties in a document has virtually disappeared. With the advent and refinement of CSS and the increasing support for it in web browsers, subsequent editions of HTML increasingly stress only using markup that suggests the semantic structure and phrasing of the document, like headings, paragraphs, quotes, and lists, instead of using markup which is written for visual purposes only, like <font> , <b> (bold), and <i> (italics). Some of these elements are not permitted in certain varieties of HTML, like HTML 4.01 Strict. CSS provides a way to separate document semantics from the content's presentation, by keeping everything relevant to presentation defined in a CSS file. See separation of style and content .

semantic HTML offers many advantages. First, it ensures consistency in style across elements that have the same meaning. Every heading, every quotation, every similar element receives the same presentation properties.

Second, semantic HTML frees authors from the need to concern themselves with presentation details. When writing the number two, for example, should it be written out in words ("two"), or should it be written as a numeral (2)? A semantic markup might enter something like <number>2</number> and leave presentation details to the stylesheet designers. Similarly, an author might wonder where to break out quotations into separate indented blocks of text - with purely semantic HTML, such details would be left up to stylesheet designers. Authors would simply indicate quotations when they occur in the text, and not concern themselves with presentation.

A third advantage is device independence and repurposing of documents. A semantic HTML document can be paired with any number of stylesheets to provide output to computer screens (through web browsers), high-resolution printers, handheld devices, aural browsers or braille devices for those with visual impairments, and so on. To accomplish this nothing needs to be changed in a well coded semantic HTML document. Readily available stylesheets make this a simple matter of pairing a semantic HTML document with the appropriate stylesheets (of course, the stylesheet's selectors need to match the appropriate properties in the HTML document).

Some aspects of authoring documents make separating semantics from style (in other words, meaning from presentation) difficult. Some elements are hybrids, using presentation in their very meaning. For example, a table displays content in a tabular form. Often this content only conveys the meaning when presented in this way. Repurposing a table for an aural device typically involves somehow presenting the table as an inherently visual element in an audible form. On the other hand, we frequently present lyrical songs — something inherently meant for audible presentation — and instead present them in textual form on a web page. For these types of elements, the meaning is not so easily separated from their presentation. However, for a great many of the elements used and meanings conveyed in HTML the translation is relatively smooth.

semantic Web

The semantic web is an evolving extension of the World Wide Web in which web content can be expressed not only in natural language , but also in a format that can be read and used by software agents , thus permitting them to find, share and integrate information more easily. It derives from W3C director Sir Tim Berners-Lee 's vision of the Web as a universal medium for data , information , and knowledge exchange.

At its core, the semantic web comprises a philosophy, a set of design principles, collaborative working groups , and a variety of enabling technologies. Some elements of the semantic web are expressed as prospective future possibilities that have yet to be implemented or realized. Other elements of the semantic web are expressed in formal specifications. Some of these include Resource Description Framework (RDF), a variety of data interchange formats (e.g. RDF/XML , N3 , Turtle , N-Triples ), and notations such as RDF Schema (RDFS) and the Web Ontology Language (OWL), all of which are intended to provide a formal description of concepts , terms , and relationships within a given knowledge domain .

Humans are capable of using the Web to carry out tasks such as finding the Finnish word for "car", to reserve a library book, or to search for the cheapest DVD and buy it. However, a computer cannot accomplish the same tasks without human direction because web pages are designed to be read by people, not machines. The semantic web is a vision of information that is understandable by computers, so that they can perform more of the tedious work involved in finding, sharing and combining information on the web.

For example, a computer might be instructed to list the prices of flat screen HDTVs larger than 40 inches with 1080p resolution at shops in the nearest town that are open until 8pm on Tuesday evenings. Today, this task requires search engines that are individually tailored to every website being searched. The semantic web provides a common standard (RDF) for websites to publish the relevant information in a more readily machine-processable and integratable form.

Tim Berners-Lee originally expressed the vision of the semantic web as follows:

I have a dream for the Web [in which computers] become capable of analyzing all the data on the Web – the content, links, and transactions between people and computers. A ‘semantic Web', which should make this possible, has yet to emerge, but when it does, the day-to-day mechanisms of trade, bureaucracy and our daily lives will be handled by machines talking to machines. The ‘intelligent agents' people have touted for ages will finally materialize. — Tim Berners-Lee , 1999

semantic publishing will benefit greatly from the semantic web. In particular, the semantic web is expected to revolutionize scientific publishing , such as real-time publishing and sharing of experimental data on the Internet. This simple but radical idea is now being explored by W3C HCLS group's Scientific Publishing Task Force .

Tim Berners-Lee has further stated:

People keep asking what Web 3.0 is. I think maybe when you've got an overlay of scalable vector graphics - everything rippling and folding and looking misty - on Web 2.0 and access to a semantic Web integrated across a huge space of data, you'll have access to an unbelievable data resource.