[[edit source](/w/index.php?title=Semantic_Web&action=edit&section=4 "Edit section's source code: Limitations of HTML")] Many files on a typical computer can be loosely divided into either human-readable documents, or machine-readable data. Examples of human-readable document files are mail messages, reports, and brochures. Examples of machine-readable data files are calendars, address books, playlists, and spreadsheets, which are presented to a user using an application program that lets the files be viewed, searched, and combined. Currently, the World Wide Web is based mainly on documents written in [Hypertext Markup Language](https://en.wikipedia.org/wiki/Hypertext_Markup_Language "Hypertext Markup Language") (HTML), a markup convention that is used for coding a body of text interspersed with multimedia objects such as images and interactive forms. Metadata tags provide a method by which computers can categorize the content of web pages. In the examples below, the field names "keywords", "description" and "author" are assigned values such as "computing", and "cheap widgets for sale" and "John Doe". ``` <meta name="keywords" content="computing, computer studies, computer" /> <meta name="description" content="Cheap widgets for sale" /> <meta name="author" content="John Doe" /> ``` Because of this metadata tagging and categorization, other computer systems that want to access and share this data can easily identify the relevant values. With HTML and a tool to render it (perhaps [web browser](https://en.wikipedia.org/wiki/Web_browser "Web browser") software, perhaps another [user agent](https://en.wikipedia.org/wiki/User_agent "User agent")), one can create and present a page that lists items for sale. The HTML of this catalog page can make simple, document-level assertions such as "this document's title is 'Widget Superstore'", but there is no capability within the HTML itself to assert unambiguously that, for example, item number X586172 is an Acme Gizmo with a retail price of €199, or that it is a consumer product. Rather, HTML can only say that the span of text "X586172" is something that should be positioned near "Acme Gizmo" and "€199", etc. There is no way to say "this is a catalog" or even to establish that "Acme Gizmo" is a kind of title or that "€199" is a price. There is also no way to express that these pieces of information are bound together in describing a discrete item, distinct from other items perhaps listed on the page. [Semantic HTML](https://en.wikipedia.org/wiki/Semantic_HTML "Semantic HTML") refers to the traditional HTML practice of markup following intention, rather than specifying layout details directly. For example, the use of `<em>` denoting "emphasis" rather than `<i>`, which specifies [italics](https://en.wikipedia.org/wiki/Italics "Italics"). Layout details are left up to the browser, in combination with [Cascading Style Sheets](https://en.wikipedia.org/wiki/Cascading_Style_Sheets "Cascading Style Sheets"). But this practice falls short of specifying the semantics of objects such as items for sale or prices. Microformats extend HTML syntax to create [machine-readable](https://en.wikipedia.org/wiki/Machine-readable_data "Machine-readable data") semantic markup about objects including people, organizations, events and products.[[19]](#cite_note-19) Similar initiatives include [RDFa](https://en.wikipedia.org/wiki/RDFa "RDFa"), [Microdata](https://en.wikipedia.org/wiki/Microdata_(HTML) "Microdata (HTML)") and [Schema.org](https://en.wikipedia.org/wiki/Schema.org "Schema.org").

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  "text": "[[edit source](/w/index.php?title=Semantic_Web&action=edit&section=4 \"Edit section's source code: Limitations of HTML\")]\n\nMany files on a typical computer can be loosely divided into either human-readable documents, or machine-readable data. Examples of human-readable document files are mail messages, reports, and brochures. Examples of machine-readable data files are calendars, address books, playlists, and spreadsheets, which are presented to a user using an application program that lets the files be viewed, searched, and combined.\n\nCurrently, the World Wide Web is based mainly on documents written in [Hypertext Markup Language](https://en.wikipedia.org/wiki/Hypertext_Markup_Language \"Hypertext Markup Language\") (HTML), a markup convention that is used for coding a body of text interspersed with multimedia objects such as images and interactive forms. Metadata tags provide a method by which computers can categorize the content of web pages. In the examples below, the field names \"keywords\", \"description\" and \"author\" are assigned values such as \"computing\", and \"cheap widgets for sale\" and \"John Doe\".\n\n```\n<meta name=\"keywords\" content=\"computing, computer studies, computer\" />\n<meta name=\"description\" content=\"Cheap widgets for sale\" />\n<meta name=\"author\" content=\"John Doe\" />\n```\n\nBecause of this metadata tagging and categorization, other computer systems that want to access and share this data can easily identify the relevant values.\n\nWith HTML and a tool to render it (perhaps [web browser](https://en.wikipedia.org/wiki/Web_browser \"Web browser\") software, perhaps another [user agent](https://en.wikipedia.org/wiki/User_agent \"User agent\")), one can create and present a page that lists items for sale. The HTML of this catalog page can make simple, document-level assertions such as \"this document's title is 'Widget Superstore'\", but there is no capability within the HTML itself to assert unambiguously that, for example, item number X586172 is an Acme Gizmo with a retail price of €199, or that it is a consumer product. Rather, HTML can only say that the span of text \"X586172\" is something that should be positioned near \"Acme Gizmo\" and \"€199\", etc. There is no way to say \"this is a catalog\" or even to establish that \"Acme Gizmo\" is a kind of title or that \"€199\" is a price. There is also no way to express that these pieces of information are bound together in describing a discrete item, distinct from other items perhaps listed on the page.\n\n[Semantic HTML](https://en.wikipedia.org/wiki/Semantic_HTML \"Semantic HTML\") refers to the traditional HTML practice of markup following intention, rather than specifying layout details directly. For example, the use of `<em>` denoting \"emphasis\" rather than `<i>`, which specifies [italics](https://en.wikipedia.org/wiki/Italics \"Italics\"). Layout details are left up to the browser, in combination with [Cascading Style Sheets](https://en.wikipedia.org/wiki/Cascading_Style_Sheets \"Cascading Style Sheets\"). But this practice falls short of specifying the semantics of objects such as items for sale or prices.\n\nMicroformats extend HTML syntax to create [machine-readable](https://en.wikipedia.org/wiki/Machine-readable_data \"Machine-readable data\") semantic markup about objects including people, organizations, events and products.[[19]](#cite_note-19) Similar initiatives include [RDFa](https://en.wikipedia.org/wiki/RDFa \"RDFa\"), [Microdata](https://en.wikipedia.org/wiki/Microdata_(HTML) \"Microdata (HTML)\") and [Schema.org](https://en.wikipedia.org/wiki/Schema.org \"Schema.org\").",
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  "heading": "Limitations of HTML",
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