Semantic HTML is the use of HTML markup to reinforce the semantics, or meaning, of the information in web pages and web applications rather than merely to define its presentation or look. Semantic HTML is processed by traditional web browsers as well as by many other user agents. CSS is used to suggest its presentation to human users.
HTML has included semantic markup since its inception. [1] In an HTML document, the author may, among other things, "start with a title; add headings and paragraphs; add emphasis to [the] text; add images; add links to other pages; [and] use various kinds of lists". [2]
Various versions of the HTML standard have included presentational markup such as <font> (added in HTML 3.2; removed in HTML 4.0 Strict), <i> (all versions) and <center> (added in HTML 3.2). There are also the semantically neutral span and div elements. Since the late 1990s when Cascading Style Sheets were beginning to work in most browsers, web authors have been encouraged to avoid the use of presentational HTML markup with a view to the separation of content and presentation. [3]
In 2001, Tim Berners-Lee participated in a discussion of the Semantic Web, where it was presented that intelligent software 'agents' might one day automatically trawl the Web and find, filter and correlate previously unrelated, published facts for the benefit of end users. [4] Such agents are not commonplace even now, but some of the ideas of Web 2.0, mashups and price comparison websites may be coming close. The main difference between these web application hybrids and Berners-Lee's semantic agents lies in the fact that the current aggregation and hybridisation of information is usually designed in by web developers, who already know the web locations and the API semantics of the specific data they wish to mash, compare and combine.
An important type of web agent that does crawl and read web pages automatically, without prior knowledge of what it might find, is the Web crawler or search-engine spider. These software agents are dependent on the semantic clarity of web pages they find as they use various techniques and algorithms to read and index millions of web pages a day and provide web users with search facilities.
In order for search-engine spiders to be able to rate the significance of pieces of text they find in HTML documents, and also for those creating mashups and other hybrids, as well as for more automated agents as they are developed, the semantic structures that exist in HTML need to be widely and uniformly applied to bring out the meaning of published information. [5]
While the true semantic web may depend on complex RDF ontologies and metadata, every HTML document makes its contribution to the meaningfulness of the Web by the correct use of headings, lists, titles and other semantic markup wherever possible. This "plain" use of HTML has been called "Plain Old Semantic HTML" or POSH. [6] The correct use of Web 2.0 'tagging' creates folksonomies that may be equally or even more meaningful to many. [5] HTML 5 introduced new semantic elements such as <section>, <article>, <footer>, <progress>, <nav>, <aside>, <mark>, and <time>. [7] Overall, the goal of the W3C is to slowly introduce more ways for browsers, developers, and crawlers to better distinguish between different types of data, allowing for benefits such as better display on browsers on different devices.
Presentational elements were not formally deprecated in HTML 4.01 and XHTML recommendations, but were recommended against. In HTML 5, some of those elements, such as <i> and <b>, are still specified as their meaning has been clearly defined "as to be stylistically offset from the normal prose without conveying any extra importance". [8] [9]
In cases where a document requires more precise semantics than those expressed in HTML alone, fragments of the document may be enclosed within span or div elements with meaningful class names [10] such as <span class="author"> and <div class="invoice">. Where these class names are also a fragment identifier within a schema or ontology, they may link to a more defined meaning. Microformats formalise this approach to semantics in HTML.
One important restriction of this approach is that such markup based on element inclusion must meet the well-formedness conditions. As these documents are broadly tree-structured, this means that only balanced fragments from a sub-tree can be marked up in this way. [11] [12] A means of marking-up any arbitrary section of HTML would require a mechanism independent of the markup structure itself, such as XPointer.
Good semantic HTML also improves the accessibility of web documents (see also Web Content Accessibility Guidelines).[ citation needed ] For example, when a screen reader or audio browser can correctly ascertain the structure of a document, it will not waste the visually impaired user's time by reading out repeated or irrelevant information when it has been marked up correctly.
In 2010, Google specified three forms of structured metadata that their systems will use to find structured semantic content within webpages. Such information, when related to reviews, people profiles, business listings, and events will be used by Google to enhance the "snippet", or short piece of quoted text that is shown when the page appears in search listings. Google specifies that that data may be given using microdata, microformats or RDFa. [13] Microdata is specified inside itemtype and itemprop attributes added to existing HTML elements; microformat keywords are added inside class attributes as discussed above; and RDFa relies on rel, typeof and property attributes added to existing elements. [14]
HyperText Markup Language or HTML is the standard markup language for documents designed to be displayed in a web browser. It defines the content and structure of web content. It is often assisted by technologies such as Cascading Style Sheets (CSS) and scripting languages such as JavaScript.
A markuplanguage is a text-encoding system which specifies the structure and formatting of a document and potentially the relationship between its parts. Markup can control the display of a document or enrich its content to facilitate automated processing.
The Semantic Web, sometimes known as Web 3.0, is an extension of the World Wide Web through standards set by the World Wide Web Consortium (W3C). The goal of the Semantic Web is to make Internet data machine-readable.
Mathematical Markup Language (MathML) is a mathematical markup language, an application of XML for describing mathematical notations and capturing both its structure and content, and is one of a number of mathematical markup languages. Its aim is to natively integrate mathematical formulae into World Wide Web pages and other documents. It is part of HTML5 and standardised by ISO/IEC since 2015.
An HTML element is a type of HTML document component, one of several types of HTML nodes. The first used version of HTML was written by Tim Berners-Lee in 1993 and there have since been many versions of HTML. The current de facto standard is governed by the industry group WHATWG and is known as the HTML Living Standard.
In web development, "tag soup" is a pejorative for syntactically or structurally incorrect HTML written for a web page. Because web browsers have historically treated structural or syntax errors in HTML leniently, there has been little pressure for web developers to follow published standards, and therefore there is a need for all browser implementations to provide mechanisms to cope with the appearance of "tag soup", accepting and correcting for invalid syntax and structure where possible.
Microformats (μF) are a set of defined HTML classes created to serve as consistent and descriptive metadata about an element, designating it as representing a certain type of data. They allow software to process the information reliably by having set classes refer to a specific type of data rather than being arbitrary. Microformats emerged around 2005 and were predominantly designed for use by search engines, web syndication and aggregators such as RSS.
In HTML, <div> and <span> tags are elements used to define parts of a document, so that they are identifiable when a unique classification is necessary. Where other HTML elements such as <p> (paragraph), <em> (emphasis), and so on, accurately represent the semantics of the content, the additional use of <span> and <div> tags leads to better accessibility for readers and easier maintainability for authors. Where no existing HTML element is applicable, <span> and <div> can valuably represent parts of a document so that HTML attributes such as class, id, lang, or dir can be applied.
GRDDL is a markup format for Gleaning Resource Descriptions from Dialects of Languages. It is a W3C Recommendation, and enables users to obtain RDF triples out of XML documents, including XHTML. The GRDDL specification shows examples using XSLT, however it was intended to be abstract enough to allow for other implementations as well. It became a Recommendation on September 11, 2007.
RDFa or Resource Description Framework in Attributes is a W3C Recommendation that adds a set of attribute-level extensions to HTML, XHTML and various XML-based document types for embedding rich metadata within Web documents. The Resource Description Framework (RDF) data-model mapping enables its use for embedding RDF subject-predicate-object expressions within XHTML documents. It also enables the extraction of RDF model triples by compliant user agents.
HTML5 is a markup language used for structuring and presenting hypertext documents on the World Wide Web. It was the fifth and final major HTML version that is now a retired World Wide Web Consortium (W3C) recommendation. The current specification is known as the HTML Living Standard. It is maintained by the Web Hypertext Application Technology Working Group (WHATWG), a consortium of the major browser vendors.
Embedded RDF (eRDF) is a syntax for writing HTML in such a way that the information in the HTML document can be extracted into Resource Description Framework (RDF). This can be of great use for searching within data.
Extensible HyperText Markup Language (XHTML) is part of the family of XML markup languages which mirrors or extends versions of the widely used HyperText Markup Language (HTML), the language in which Web pages are formulated.
Cascading Style Sheets (CSS) is a style sheet language used for specifying the presentation and styling of a document written in a markup language such as HTML or XML. CSS is a cornerstone technology of the World Wide Web, alongside HTML and JavaScript.
Microdata is a WHATWG HTML specification used to nest metadata within existing content on web pages. Search engines, web crawlers, and browsers can extract and process Microdata from a web page and use it to provide a richer browsing experience for users. Search engines benefit greatly from direct access to this structured data because it allows them to understand the information on web pages and provide more relevant results to users. Microdata uses a supporting vocabulary to describe an item and name-value pairs to assign values to its properties. Microdata is an attempt to provide a simpler way of annotating HTML elements with machine-readable tags than the similar approaches of using RDFa and microformats.
HTML attributes are special words used inside the opening tag to control the element's behaviour. HTML attributes are a modifier of a HTML element type. An attribute either modifies the default functionality of an element type or provides functionality to certain element types unable to function correctly without them. In HTML syntax, an attribute is added to a HTML start tag.
XHTML+RDFa is an extended version of the XHTML markup language for supporting RDF through a collection of attributes and processing rules in the form of well-formed XML documents. XHTML+RDFa is one of the techniques used to develop Semantic Web content by embedding rich semantic markup. Version 1.1 of the language is a superset of XHTML 1.1, integrating the attributes according to RDFa Core 1.1. In other words, it is an RDFa support through XHTML Modularization.
The Web platform is a collection of technologies developed as open standards by the World Wide Web Consortium and other standardization bodies such as the Web Hypertext Application Technology Working Group, the Unicode Consortium, the Internet Engineering Task Force, and Ecma International. It is the umbrella term introduced by the World Wide Web Consortium, and in 2011 it was defined as "a platform for innovation, consolidation and cost efficiencies" by W3C CEO Jeff Jaffe. Being built on The evergreen Web has allowed for the addition of new capabilities while addressing security and privacy risks. Additionally, developers are enabled to build interoperable content on a cohesive platform.
Schema.org is a reference website that publishes documentation and guidelines for using structured data mark-up on web-pages. Its main objective is to standardize HTML tags to be used by webmasters for creating rich results about a certain topic of interest. It is a part of the semantic web project, which aims to make document mark-up codes more readable and meaningful to both humans and machines.
