Chapter 9 Hypertext

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Chapter 9Hypertext
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.

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Key Points

• Navigation in a large hypertext collection is
  problematical. Suitable structures are still
  undeveloped.

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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 Xeroxs NoteCards
• Scripting HyperTalk
• WWW

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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

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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

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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

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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

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Hierarchical Structure

• Organizational and navigational framework
• Frame-based display
• Navigation within a hierarchy
• Hybrid structure
• Sequential and hierarchical