In this section we will continue discussing graphic vocabularies and the problem of browsing of the knowledge bases. Yet the main goals of this section is to introduce domain views. As an ontology or domain model become large it becomes increasingly difficult to browse it. The domain views provide a technique to elicit tractable and meaningful portions of the ontology. We shall introduce 3 types of views -relation views, object views , and query views. Let us consider them in sequence.
Relation Views
An ontology can be considered as a set of nodes and relations represented by arrows. Typically we have such relations as isa:, isa::, attributes, signatures. We can essentially simplify the view of ontology if we depict only one or two types of relations hiding all other. For example in context of example from previous section, if we focus on isa:: relations we shall view only the class hierarchy -the Linnaean taxonomy pertained to our ecosystem. If we focus on relation eats, living aside all other , we shall see only the food web. Here is the typical relation view. To increase the readability we may use graphic vocabularies along with the views. The following example illustrates that conventional food web picture may be obtained with the help of relation view.
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To specify a relation view user has to select the names of relations s/he wishes to view, and choose if s/he wishes to consider signatures, exclude them, or view only signatures and also choose if predefined graphic symbols for relations should be used. Thus specification of a relation view can be accomplished with merely two groups of radio buttons and one text area or list box with enabled option for multiple choices.
Object Views
Sometimes a user may be interested to view relations pertained to a specific object be it class or instance. Object views of depth one depict only the object and those related to it via any relations. Object view of depth N built via recursive procedure which constructs an object view of depth one for the given object and then takes every object from this view and constructs an object view of depth N-1 for each. Here is an example of object view:
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To specify an object view user must specify an object and the depth. Object can be specified via typing its name into a textbox or by a mouse click. It is possible also to distinguish between bidirectional and unidirectional object views. The latter will depict only the attributes and values of the given object, while former will depict also those objects which have the given object as a value of their attributes.
Query views
The query view outputs all objects and relation generated by a query . This type of views is the most powerful. The effect of two previous view types may be also achieved via query vies. Here is the example:
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Although query view provides an ultimate power of ontology browsing it would require a mechanism for specification of the queries. This mechanism may not be really as simple as the ones needed to specify relation and object views.
C 2003 S. Krivov Send your comments to skrivov@zoo.uvm.edu