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Collection of (1) Meta-network That is, a

1 Collection of (1) Meta-network That is, a (2) of (3) Uses a standard set of protocols Also uses standards d for structuring t the information transferred (1) I (2) S (3) P allow subscribers to connect to the (4) often provide basic services such as (5) (6) 1

2 Transportation analogy sidewalks, streets, boulevards, highways and interstates Backbone is the internet equivalent of the (1) (in the transportation analogy) NAPs: Network Access Points connect the backbone to regional networks How could you find out where the nearest NAP is? 1989 (1) Who? working for CERN Wanted a standardized way in which scientists could communicate with each other Codified HTML, based on SGML Hyperlinking used - Not a new concept but used in a new way Web metaphor emphasizes the intricate interconnectedness of the WWW Milestone: 1993-National Center for Supercomputing Applications (NCSA) develops Mosaic (2) What was Mosaic? Marc Andreesen at U of Illinois Later Mosaic becomes (3) File Transfer Protocol Prior to the web, the way to transfer files over the Internet 2

3 Transmission Control Protocol / (over) Internet Protocol Packet switched break down large chunks of data into smaller ones called packets IP moves these packets from node to node Delivery is based on unique IP numbers or addresses At delivery, TCP verifies that all the info is intact and reassembles it Hypertext Links that make the web interconnected Hypertext Transfer Protocol Protocol use to send information across the World Wide Web HTTP request sent from user s (1) to the (2) and the response is the web page displayed in the (3) XHTML a set of codes or commands that describe the structure of the text and images The browser interprets how text and images appear to the user Uses tags open and close tags <h1></h1> to mark up the text for structure <h1>this is a Heading</h1> <head></head> defines the information in the document header 3

4 (1) that sends requests to the HTTP server Capable of displaying the XHTML and content ( and other markup) that is sent in response Netscape Navigator Internet Explorer Non-graphical, text only browsers Early development ASCII text only Very fast Uniform Resource Locator (URL) or Uniform Resource Indicator (URI) textual address of where the information is stored Each part of the URL has a specific meaning that is related to the information s location on the World Wide Web http-indicates the protocol to be used could be ftp or other domain name that identifies the web server where the files are stored cg/courses/cgt111 directory path on the web server TypeHandout.pdf file name of requested document The text version of an IP address Each domain name has a unique IP address associated with it 4

5 An indication of the kind of domain.edu-educational.gov-government.com-commercial.mil-military military.net-networking.org-nonprofit organization.biz.info Other? Second Level Domain The part of the address that actually identifies the organization.uh in the pervious example 5

6 What was wrong with HTML? Web is not just for the PC anymore Accessed by a variety of devices Cell phones Personal Digital it Assistants t (PDAs) Pagers Some new devices are not visually oriented Changes are needed to accommodate these devices HTML (Hypertext Markup Language) Simple markup language for structuring a web document Fixed set of tags to define structure XML (Extensible Markup Language) Focuses on what the data is XHTML (Extensible Hypertext Markup Language) Reformulation of HTML into an XML application W3C recommendation SGML (Standard Generalized Markup Language) Standard published in 1983 Defines document structure Complex and difficult to learn HTML (Hypertext Markup Language) First offspring of SGML Uses grammar of SGML Limited of number of tags (grew) 6

7 XML (Extensible Markup Language) Compatible with SGML Used to Define type of information what the data is Structured, extensible XHTML (Extensible Hypertext Markup Language) Combines advantages of sibling languages Uses elements of HTML and syntax of SGML Has the structure of XML Extensibility can be extended beyond its predefined elements Portability make Web documents accessible across platforms Not sloppy XHTML redefines HTML using XML rules XHTML documents differ in several ways Must be well-formed Element and attribute names must be in lower case Attribute values must always be quoted No attribute minimization Use Document Type Definitions Use XML namespaces 7

8 Must have opening and closing tag In XHTML we always close the tag like: <p>this is a properly p closed XHTML tag.</p> <p>with a second paragraph.</p> Properly nested tags No overlapping elements <p>this is <em>emphasized text</em>. The emphasis tags are properly nested inside the paragraph tags. Emphasis tags imply a structure but not a format. Style sheets define how the browser renders emphasis. It is italics, by default, in many browsers.</p> Single-sided elements are elements that do not markup text content. They must be properly closed. <p>the tags following the closing p tag are properly closed, single-sided XHTML tags.</p> <br /> <img src= porky.jpg alt= Porky Pigg /> 8

9 XML is case sensitive. XHTML is an application of XML. Thus, it is also case-sensitive. Element and attribute names must be in lower case. <p>this is a properly closed XHTML tag. Note that lower case letters are used in the tag.</p> <p>here is an anchor tag used to create hypertext.</p> <a href= first.html >Link to the first page</a> Attribute values must always be inside quotes <div id= news >The news of the day is that the President will deliver his State t of the Union Address tonight.</div> <img src= president_making_speech.jpg alt= The President making a speech /> All attributes must have values, some attributes are required. <div id= news >The news of the day is that the President will deliver his State t of the Union Address tonight.</div> <img src= president_making_speech.jpg alt= The President making a speech /> 9

10 Must include declaration of document type and url to Document Type Definition (DTD) DTD Defines the legal structure, elements, and attributes that are available for use in a document that complies with the DTD XHTML can use one of three DTDs Strict - Document will conform exactly to the XHTML 1.0 standard Transitional - Used when old HTML markup needs to be accommodated Frameset - Used when the document needs to use frames Valid XHTML documents must meet the following criteria: Well-formed Validate against one of the three DTDs Root element must be <html> and designate XHTML namespace using xmlns attribute Doctype declaration must be in document 10

11 W3C provides a validation tool 11

Collection of (1) Meta-network. Uses a standard set of protocols Also uses standards for structuring the information transferred

Collection of (1) Meta-network That is, a (2) of (3) Uses a standard set of protocols Also uses standards for structuring the information transferred Collection of (1)_networks_ Meta-network That is, a