The World Wide Web (abbreviated as WWW or W3, commonly known as the Web), is a system of interlinked hypertext documents accessed via the Internet. With a web browser, one can view web pages that may contain text, images, videos, and other multimedia, and navigate between them via hyperlinks. WWW technology is maintained and developed by the World Wide Web Consortium (W3C), although the Internet Engineering Task Force (IETF) standardizes the technologies. The W3C has listed the following three goals for the WWW: universal access of web resources (by everyone everywhere), effectiveness of navigating available information, and responsible use of posted material.
History of the WWW
Amazingly, one of the most predominant networked multimedia applications has its roots in nuclear physics! – As noted in the previous section, Tim Berners – Lee proposed the World Wide Web to CERN (European Center for Nuclear Research) as a means for organizing and sharing their work and experimental results. The following is a short list of important dates in the creation of the WWW:
1960s It is recognized that documents need to have formats that are human – readable and that identify structure and elements. Charles Goldfarb, Edward Mosher, and Raymond Lone developed the Generalized Markup Language (GML) for IBM.
1986 The ISO released a final version of the Standard Generalized Markup Language (SGML), mostly based on the earlier GML.
1990 With approval from CERN, Tim Bemers – Lee started developing a hypertext server, browser, and editor on a NeXTStep workstation. He invented hypertext markup language (HTML) and the hypertext transfer protocol (HTTP) for this purpose.
1. NCSA released an alpha version of Mosaic based on the version by Marc Andreessen for the X Windows System. This was the first popular browser. Microsoft’s Internet Explorer is based on Mosaic.
2. Marc Andreessen and some colleagues from NCSA joined Dr. James H. Clark (also the founder of Silicon Graphics Inc.) to form Mosaic Communications Corpora tion. In November, the company changed its name to Netscape Communications Corporation.
1998 The W3C accepted XML version 1.0 specifications as a Recommendation. XML is the main focus of the W3C and supersedes HTML.
HyperText Transfer Protocol (HTTP)
The Hypertext Transfer Protocol (HTTP) is an application protocol for distributed, collaborative, hypermedia information systems. HTTP is the foundation of data communication for the World Wide Web. HTTP was originally designed for transmitting hypermedia, but it also supports transmission of any file type.
Hypertext is a multi – linear set of objects, building a network by using logical links (the so – called hyperlinks) between the nodes (e.g. text or words). HTTP is the protocol to exchange or transfer hypertext.
The standards development of HTTP was coordinated by the Internet Engineering Tas Force (IETF) and the World Wide Web Consortium (W3C), culminating in the publication of a series of Requests for Comments (RFCs), most notably RFC 2616 (June 1999), which defines HTTP / 1.1, the version of HTTP in common use.
HyperText Markup Language (HTML)
HyperText Markup Language (HTML) is the main markup language for displaying web pages and other information that can be displayed in a web browser.
HTML is written in the form of HTML elements consisting of tags enclosed in angle brackets (like <html>), within the web page content. HTML tags most commonly come in pairs like <h1> and </h1>, although some tags, known as empty elements, are unpaired, for example<img>.
A very simple HTML page is as follows
The first tag in a pair is the start tag, the second tag is the end tag (they are also called opening tags and closing tags). In between these tags web designers can add text, tags, comments and other types of text – based content.
The purpose of a web browser is to read HTML documents and compose them into visible or audible web pages. The browser does not display the HTML tags, but uses the tags to interpret the content of the page.
HTML elements form the building blocks of all websites. HTML allows images and objects to be embedded and can be used to create interactive forms. It provides a means to create structured documents by denoting structural semantics for text such as headings, paragraphs, lists, links, quotes and other items. It can embed scripts in languages such as JavaScript which affect the behavior of HTML webpages.
Web browsers can also refer to Cascading Style Sheets (CSS) to define the appearance and layout of text and other material. The W3C, maintainer of both the HTML and the CSS standards, encourages the use of CSS over explicitly presentational HTML markup.
Extensible Markup Language (XML)
Extensible Markup Language (XML) is a markup language that defines a set of rules for encoding documents in a format that is both human – readable and machine – readable. It is defined in the XML 1.0 Specification produced by the W3C, and several other related specifications, all gratis open standards.
The design goals of XML emphasize simplicity, generality, and usability over the Internet. It is a textual data format with strong support via Unicode for the languages of the world. Although the design of XML focuses on documents, it is widely used for the representation of arbitrary data structures, for example in web services.
Many application programming interfaces (APIs) have been developed for software developers to use to process XML data, and several schema systems exist to aid in the definition of XML – based languages.
As of 2009, hundreds of XML – based languages have been developed, including RSS, Atom, SOAP, and XHTML. XML – based formats have become the default for many office – productivity tools, including Microsoft Office (Office Open XML), Open Office.org and LibreOffice (Open Document), and Apple’s iWork. XML has also been employed as the base language for communication protocols, such as XMPP.
In addition to XML specifications, the following XML – related specifications are stan dardized:
1. XML Protocol. Used to exchange XML information between processes. It is meant to supersede HTTP and extend it as well as to allow interprocess communications across networks.
2. XML Schema. A more structured and powerful language for defining XML data types (tags). Unlike a DTD, XML Schema uses XML tags for type definitions.
3. XSL. This is basically CSS for XML. On the other hand, XSL is much more complex, having three parts: XSL Transformations (XSLT), XML Path Language (XPath), and XSL Formatting Objects,
4. SMIL: Synchronized Multimedia Integration Language, pronounced “smile”. This is a particular application of XML (globally predefined DTD) that permits spec ifying temporally scripted interaction among any media types and user input. For example, it can be used to show a streaming video synchronized with a slide show presentation, both reacting to user navigation through the slide show or video.
Synchronized Multimedia Integration Language (SMIL)
Synchronized Multimedia Integration Language is a World Wide Web Consortium recommended Extensible Markup Language (XML) markup language to describe multimedia presentations. It defines markup for timing, layout, animations, visual transitions, and media embedding, among other things. SMIL allows presenting media items such as text, images, video, audio, links to other SMIL presentations, and files from multiple web servers. SMIL markup is written in XML, and has similarities to HTML.
The W3C established a Working Group in 1997 to come up with specifications for a multimedia synchronization language. That group produced specifications for SMIL 1.0 that became a Recommendation in June 1998. As HTML was being redefined in XML (XHTML specifications), so too did SMIL 1.0, with some enhancements. SMIL 2.0, which also provides integration with HTML, was accepted as a Recommendation in August 2001.
SMIL 2.0 is specified in XML using a modularization approach similar to the one used in XHTML. All SMIL elements are divided into modules — sets of XML elements, attributes, and values that define one conceptual functionality. In the interest of modularization, not all available modules must be included for all applications. For that reason, Language Profiles are defined, specifying a particular grouping of modules. Particular modules may have integration requirements a profile must follow. SMIL 2.0 has a main language profile that includes almost all SMIL modules, a Basic profile that includes only modules necessary to support basic functionality, and an XHTML+SMIL profile designed to integrate HTML and SMIL. The latter includes most of the XHTML modules, with only the SMIL timing modules (but not structure modules — XHTML has its own structure modules) added.
The SMIL language structure is similar to XHTML. The root element is smil, which contains the two elements head and body, head contains information not used for synchronization — meta information, layout information, and content control, such as media bitrate body contains all the information relating to which resources to present, and when.
Three types of resource synchronization (grouping) are available: seq, par, and excl. seq specifies that the elements grouped are to be presented in the specified order (sequentially). Alternatively, par specifies that all the elements grouped are to be presented at the same time (in parallel), excl specifies that only one of the grouped elements can be presented at a time (exclusively); order does not matter.
Let’s look at an example of SMIL code:
A SMIL document can optionally use the < IDOCTYPE. . . > directive to import the SMIL DTD, which will force the interpreter to verify the document against the DTD. A SMIL document starts with <smil> and specifies the default namespace, using the xmlns attribute. The <head> section specifies the author of the document. The body element contains the synchronization information and resources we wish to present.
In the example given, a video source called “authorview.inpg”, an audio source, “authorview.wav”, and an HTML document at ” are presented simultaneously at the beginning. When the video ends, the image “on a goodday. jpg” is shown, while the audio and the HTML document are still presented. At this point, the audio will thank the listeners and conclude the interview. Additional information on SMIL specifications and available modules is available on the W3C web site.
