1. Chapter 9 Hypertext

2. Key Points ► Hypertext is text augmented with links that point to other pieces of text. ► Hypertext has a relatively long history, but is now dominated by the World Wide Web.

3. Key Points ► Links may be simple and uni-directional, regional or bi-directional, or may be generalized as multi-links. ► PDF supports uni-directional regional links. ► HTML supports simple uni-directional links using URLs (Uniform Resource Locators) to identify destinations.

4. Key Points ► A full URL consists of a protocol, a domain name and a path. Partial URLs omit leading components. A fragment identifier is used to identify a location within a document. ► An A (anchor) element with an href attribute is used as the source of a link; with a name attribute it functions as the destination. ► XPointer and XLink extend the HTML linking mechanism to support more flexible and general links in XML.

5. Key Points ► Navigation in a large hypertext collection is problematical. Suitable structures are still undeveloped.

6. Introduction ► Hypertext is text augmented with links- points to other pieces of text, possibly elsewhere in the same documents, or on another document, perhaps stored at a different location. ► Hypertext, Hypermedia, multimedia

7. History ► 1945, Memex, Vannevar Bush, browsing and annotating ► 1960-1970, several experimental systems ► Information kiosks ► 1987, Hypercard  Apple, free  Hypercard stacks  Form Xerox’s NoteCards  Scripting: HyperTalk ► WWW

8. Nature ► Non-linear fashion ► Cross-reference

9. Link ► Fig. 9.1, uni-directional links ► Fig. 9.2 Regional, bi-directional and multi-links  XML ► PDF  uni-directional, regional link

10. HTML ► CGI: common gateway interface ► Partial URLs,.,.. ► Fragment identifier # ► Href attribute : source of a link ► Fig. 9.4 Links and Anchors ► Fig. 9.5 Frame-based navigation  Target attribute ► _self, _blank, _top, _parent

11. XPointer and XLink ► XPointer: fragment identifier  Defining a region in a document ► Regional hypertext links ► X Two sorts  Simple and extended  Inline, out-of-line : anchors ► Document tree  Relationship, Fig. 9.6  XPointer: providing a flexible means of locating elements within documents  id(orinoco).span(child(3),child(6)) ► Third through sixth child elements ► XLink  Simple and extended  Inline, out-of-line

12. Navigation ► Lost in hyperspace ► Graphical views of link structure ► Fish-eye ► Go back, history list, bookmark ► Small index  Manual  Automatic: robots, spiders, web crawler ► AltaVista  Oldest  Brute force approach ► META elements: data about data  Name, content attributes  Description and keywords

13. Hierarchical Structure ► Organizational and navigational framework ► Frame-based display  Navigation within a hierarchy ► Hybrid structure  Sequential and hierarchical