University of Malta CSA3080: Lecture 8 © Chris Staff 1 of 21 CSA3080: Adaptive Hypertext Systems I Dr. Christopher Staff Department of Computer Science & AI University of Malta Lecture 8: Hypertext Issues and the WWW

University of Malta CSA3080: Lecture 8 © Chris Staff 2 of 21 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

University of Malta CSA3080: Lecture 8 © Chris Staff 3 of 21 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”…

University of Malta CSA3080: Lecture 8 © Chris Staff 4 of 21 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 ( FID= &CFTOKEN= ). Entire issue devoted to “Seven Issues” FID= &CFTOKEN= –Seven Issues, Revisited. Panel Session, Hypertext ‘02.

University of Malta CSA3080: Lecture 8 © Chris Staff 5 of 21 The Seven Issues Search and Query Composites Virtual Structures and dynamic information Computation Versioning Support for collaborative work Extensibility and Tailorability

University of Malta CSA3080: Lecture 8 © Chris Staff 6 of 21 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!)

University of Malta CSA3080: Lecture 8 © Chris Staff 7 of 21 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!

University of Malta CSA3080: Lecture 8 © Chris Staff 8 of 21 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…

University of Malta CSA3080: Lecture 8 © Chris Staff 9 of 21 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!

University of Malta CSA3080: Lecture 8 © Chris Staff 10 of 21 Issues in Hypertext Versioning –Shudder!!!! –Some systems/editors provide versioning (e.g., SCCS for source code development) –Web absolutely does not!

University of Malta CSA3080: Lecture 8 © Chris Staff 11 of 21 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

University of Malta CSA3080: Lecture 8 © Chris Staff 12 of 21 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

University of Malta CSA3080: Lecture 8 © Chris Staff 13 of 21 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?

University of Malta CSA3080: Lecture 8 © Chris Staff 14 of 21 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 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.

University of Malta CSA3080: Lecture 8 © Chris Staff 15 of 21 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

University of Malta CSA3080: Lecture 8 © Chris Staff 16 of 21 WWW and DHRM DHRMWWW LinksBidirectional, n-ary Separate from doc Unidirectional, Unary Embedded in doc Authorship (link creation)AnyoneDocument owner Dangling linksNot allowedAllowed Search/Component resolution Explicit supportNot supported Dynamic linksSupported “Aware” of surroundingsNode knows parents/children Node knows children only DynamicityBuilt into modelProvided by external programs

University of Malta CSA3080: Lecture 8 © Chris Staff 17 of 21 WWW and DHRM DHRMWWW Link semanticsPossible, through presentation specification No Composite nodesYes, but not implementedMedia composition, Frames, HTML Objects Link maintenanceYes, deleting component, deletes dependencies Difficult Adding links to existing components YesNo Overlapping link anchorsSupportedNo Destination anchor pointDocument, span (beginning and end) Document, offset (beginning, no end)

University of Malta CSA3080: Lecture 8 © Chris Staff 18 of 21 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

University of Malta CSA3080: Lecture 8 © Chris Staff 19 of 21 Semantic Web WWWSemantic Web LinksUnidirectional, Unary Embedded in doc Bidirectional, n-ary Separated from document Authorship (link creation)Document ownerAnyone Dangling linksAllowed Search/Component resolution Not supportedIndirectly supported through, eg, UDDI Dynamic linksSupported “Aware” of surroundingsNode knows children onlyYes, though link separation DynamicityProvided by external programs May be supported

University of Malta CSA3080: Lecture 8 © Chris Staff 20 of 21 Semantic Web WWWSemantic Web Link semanticsNoYes, though as yet no standard Composite nodesMedia composition, Frames, HTML Objects As Web, rather than as DHRM Link maintenanceDifficultNot known yet Adding links to existing component NoNot known yet Overlapping link anchorsNoPossibly, but might be considered error Destination anchor pointDocument, offset (beginning, no end) As DHRM

University of Malta CSA3080: Lecture 8 © Chris Staff 21 of 21 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