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Semantic-Based Navigation in Open Spaces 275
Figure 10-2. Presentation window without a specific center.
10.2 Searching by Means of Navigation
Query-by-example (Geman, 2006) and view-based approaches enable users to search by
means of navigation. More specifically, they allow users to construct search queries via
navigation with the immediate evaluation of the query and optional query modification
and/or refinement.
Faceted browsers as examples of view-based search allow users to navigate the associated
faceted classification of the information space. Their link (i.e., facet and restriction)
selection is transformed into a search query effectively leading to visual query construction.
This approach requires the existence of a (manually) predefined faceted classification
scheme that is used to construct the faceted browser interface.
Due to the availability of metadata in a Semantic Web scenario, a faceted classification
scheme can be (semi)automatically derived from the used ontology scheme(s). Moreover,
even greater expressive power can be achieved by using the entire set of available
metadata and its possible aggregations for view-based search. Ultimately, this allows users
to visually construct and evaluate semantic queries (e.g., in SeRQL or SPARQL), which are
otherwise difficult to write even for experienced users, thus negating one principal disadvantage
of semantic search.
10.3 Navigation Models
Navigation models correspond to the specific organization of navigation in a particular
information space such as a web site. Presently, different navigation models or their combinations
are employed based on the application domain and the respective application
goals (Rocketface Graphics, 2007).
Furthermore, no clear classification of individual navigation models seems to exist, as
many sources use the same names for different models. Based on different sources, we
devised the following classification of navigation models:
− Linear navigation – the successive browsing through a list of pages, such as search results
returned from a search engine.
− Hierarchical navigation – the browsing through a hierarchical (tree) structure of a site
using the main menu in large web sites or online shops.