Hi all,
I'd like to take advantage of this discussion to propose a different point of view to analyze the various aspects being discussed, which is the one we have been adopting in our work on Web application design methods for more than 10 years now, even before the Semantic Web.

I will try to be very brief, giving pointers to more detailed arguments and explanations.

A web application (semantic or not...) is seen as a way for a user (later this could be substituted by agent) to manipulate "information items" in order to perform a task. These information items may be based (but are typically NOT the same as) from data that is stored in some database or repository; rather, they are normally "views" (similar to DB views) over some information domain. These views are defined depending on the particular set of tasks being supported. One of the primary modes to access these information items is through navigation, which therefore (and for other reasons, see [1] merit its own separate model. This model is still "abstract", in the sense that it provides a navigation topology for users to navigate through items as their task requires. Furthermore, this is *independent* of particular interface models. In other words, the same navigation topology may be supported by several alternative interfaces (ie, layouts, widgets and operations).
A separate concern is, given a particular topology, what is a good interface design to allow the user to navigate in it.

I have the impression that much of the discussion in this thread has mixed the two aspects, and it might be useful to separate them.

As part of this research, the notion of "set-based navigation" has been proposed as a design pattern already back in 1997 (see references in [2]). In particular, the SHDM method has incorporated them as design primitives, which are supported in the HyperDE environment ([3,4]), which provides a language to specify these navigations structures in a concise way, and to generate running code. (It is a based on Ruby on Rails, but uses RDF instead of relational data). Many of the tasks described in the example could be supported with a navigation model directly supported by the method, but with a different interface. And, could also provide the access to the data itself as Kingsley advocates.

The work in these publications does not address so much the INTERFACE aspects of the discussion (actually there are some, but this would be a whole separate discussion). I believe David's contributions are directly applicable at the interface level, regardless of the underlying navigation model, and could be incorporated into the method.

We are also currently working on this part and we should have an alternative model and prototype to show very soon.


[1] ROSSI, G.; SCHWABE, D.; LYARDET, F.; "Web Application Models Are More Than Conceptual Models", Proceedings of the World Wild Web and Conceptual Modeling'99 Workshop, ER'99 Conference, Paris, France, Lecture Notes in Computer Science 1727 pp 239-253, Springer, November 1999, ISBN: 3-540-66653-2.

[2] http://www.tecweb.inf.puc-rio.br/navigation/context/o_7aa7f5b7%401

[3] http://www.tecweb.inf.puc-rio.br/hyperde, freely downloadable.

[4] NUNES, D.; SCHWABE, D.; "Rapid Prototyping of Web Applications combining Domain Specific Languages and Model Driven Design", Proceedings of the 6th International Conference on Web Engineering, ICWE 2006, Palo Alto, California, USA, ACM International Conference Proceeding Series pp 153-160, ACM Press, July 2006, ISBN: 1-59593-352-2.
Daniel Schwabe
Tel:+55-21-3527 1500 r. 4356
Fax: +55-21-3527 1530
Dept. de Informatica, PUC-Rio
R. M. de S. Vicente, 225
Rio de Janeiro, RJ 22453-900, Brasil