CSA3080: Adaptive Hypertext Systems I

1 of [email protected] University of Malta

CSA3080: Lecture 8© 2003- Chris Staff

CSA3080:Adaptive Hypertext Systems I

Dr. Christopher StaffDepartment of Computer Science & AI

University of Malta

Lecture 8:Hypertext Issues and the WWW



Aims and Objectives

• DHRM has very few implementation examples• The WWW, while not DHRM-conformant, is

the single largest and most popular example of a distributed hypertext system

• There are general hypertext issues, which DHRM attempted to address

• The implementation of the WWW has led to other issues, which AHS attempt to address



Issues in Hypertext

• Halasz (again :-)) wrote “Reflections…” in 1987• It re-surfaces frequently at conferences on Hypertext• Provoking much discussion and updating• Halasz believed that “hypertext” would “disappear”,

becoming an underlying mechanism for storing and linking information

• Hypertext is still very much “in our face”…



Issues in Hypertext

• “Seven Issues” References:– Reflections on NoteCards: seven issues for the next generation of hypermedia

systems Frank,G. Halasz July 1988 Communications of the ACM, Volume 31, Issue 7

– ACM Journal of Computer Documentation (JCD), Volume 25, Issue 3 (http://portal.acm.org/toc.cfm?id=507317&type=issue&coll=ACM&dl=ACM&CFID=14254782&CFTOKEN=22435962). Entire issue devoted to “Seven Issues”

– Seven Issues, Revisited. Panel Session, Hypertext ‘02.



The Seven Issues

• Search and Query

• Composites

• Virtual Structures and dynamic information

• Computation

• Versioning

• Support for collaborative work

• Extensibility and Tailorability



Issues in Hypertext

• Search and Query– as part of the hypertext model!– Current generation web has 3rd party search engines– Semantic Web *may* be able to refer to objects via

their content, rather than URL (or at least, do it seamlessly!)



Issues in Hypertext

• Composites– Web still doesn’t really support composites, though

it can be achieved through dynamic HTML • But watch out for the Dark Web!



Issues in Hypertext

• Virtual structures and dynamic information– So that the network can reconfigure itself according

to the information it contains– Self-repairing links, links which bind to the best

destination when it becomes available– Web approximates by redirecting to relocated

information…



Issues in Hypertext

• Computation– The end of a link can be a computation– The computation can decide what destination to

visit, etc.– Web can do… e.g.., search engines!



Issues in Hypertext

• Versioning– Shudder!!!!– Some systems/editors provide versioning (e.g.,

SCCS for source code development)– Web absolutely does not!



Issues in Hypertext

• Support for collaborative work– Web/internet is a collaborative place. We are

sometimes aware of other people in this space– Yet collaboration on, say, development of a web site

is not possible within the Web (i.e., there is no explicit support for it).

– Web site updating is merely replace currently live page in Document directory

– No locking, etc., of files supported



Issues in Hypertext

• Extensibility and tailorability– The “programmable” Web– Servers can be independently configured/extended– Plug-ins increase support for doc types– Web browsers can be configured for individual user,

etc



WWW

• The WWW is the single largest example of a distributed hypertext system

• But is it a good example of a hypertext system?

• And does it really matter if it’s a good example?



WWW

• The WWW was not developed with a formal model in mind

• Based on the concept of a Uniform Document Identifier, HTTP, and a standard markup language (HTML)

• TCP/IP used as the transport protocol• Link source is marked by <A HREF> tag, with an

embedded destination• Reference:

– Berners-Lee, T., et. al., 1994, “The World-Wide Web” in Communications of the ACM, Vol. 37, No. 8. August 1994.



WWW

• Simple model, yet powerful

• Can share documents across the globe

• Anyone can author a Web page

• With extensions to original model, can create pages dynamically

• Can manipulate multimedia data

• HTML still presentation markup language



WWW and DHRMDHRM WWW

Links Bidirectional, n-ary

Separate from doc

Unidirectional, Unary

Embedded in doc

Authorship (link creation) Anyone Document owner

Dangling links Not allowed Allowed

Search/Component resolution

Explicit support Not supported

Dynamic links Supported Supported

“Aware” of surroundings Node knows parents/children

Node knows children only

Dynamicity Built into model Provided by external programs



WWW and DHRMDHRM WWW

Link semantics Possible, through presentation specification

No

Composite nodes Yes, but not implemented Media composition,

Frames, HTML Objects

Link maintenance Yes, deleting component, deletes dependencies

Difficult

Adding links to existing components

Yes No

Overlapping link anchors Supported No

Destination anchor point Document, span (beginning and end)

Document, offset (beginning, no end)



Semantic Web

• Next generation web attempts to overcome some of these problems

• Thing is, “fixes” are built on top of existing structure, rather than bottom-up re-modelling



Semantic Web

WWW Semantic Web

Links Unidirectional, Unary

Embedded in doc

Bidirectional, n-ary

Separated from document

Authorship (link creation) Document owner Anyone

Dangling links Allowed Allowed

Search/Component resolution

Not supported Indirectly supported through, eg, UDDI

Dynamic links Supported Supported

“Aware” of surroundings Node knows children only Yes, though link separation

Dynamicity Provided by external programs

May be supported



Semantic Web

WWW Semantic Web

Link semantics No Yes, though as yet no standard

Composite nodes Media composition,

Frames, HTML Objects

As Web, rather than as DHRM

Link maintenance Difficult Not known yet

Adding links to existing component

No Not known yet

Overlapping link anchors No Possibly, but might be considered error

Destination anchor point Document, offset (beginning, no end)

As DHRM



So… does it matter?

• The (Semantic) Web will address some of the concerns in Seven Issues (but don’t forget about the other issues addressed by AHS!)

• SemWeb promises to become a knowledge base that may eventually remove the need for user navigation all together

Documents

CSA3080: Adaptive Hypertext Systems I