Intuitive ontology visualization is a key for their learning, exchange, as well as their usage in conceptual modeling. OWLGrEd is a visual tool for compact graphical UML-style rendering and editing of OWL 2.0 ontologies. Here we introduce into OWLGrEd visualization annotations that allow defining custom visual presentations of ontology entities on the basis of annotations attached to these entities. The introduced mechanism of attaching visual annotations to annotation properties used in the ontology, besides being convenient for attaching graphical shape to user-defined annotations, appears to be powerful enough to cover visualization of e.g. UML stereotypes and other UML constructs that do not have direct counterpart in the "logic" part of OWL.
Intuitive ontology visualization is a key for their learning, exchange, as well as their
usage in conceptual modeling. There are a number of tools (e.g. [
Although OWLGrEd can be successfully used for ontology presentation and
editing in a UML-style graphical form (cf. [
There are also natural modeling constructs in UML that do not have direct counterpart in OWL, such as stereotypes, composition relation and derived union of properties (or “abstract” property A, not having other subject-object pairs than those of union of B and C). The visual annotation framework that we introduce in this paper allows both visual effect specification for user-defined annotations and visual modeling of the mentioned “advanced” UML concepts (these concepts may be said to correspond to “user-defined” annotations from OWL perspective, as well).
In what follows, after brief reviewing of basic OWLGrEd ontology modeling facilities we proceed to the main point of outlining the visual annotation framework and some its usage examples, including advanced UML construct modeling. 2
OWLGrEd provides graphical notation for OWL, based on UML class diagrams. We
show OWL classes as UML classes, data properties as class attributes, object
properties as associations, individuals as objects, etc. We enrich the UML class
diagrams with the following new extension notations (cf. [
Plant
Tree is-part-of only Leaf is-part-of
{tran}
Tasty-plant eats only
Thing {owl} eaten-by eats eaten-by-animal {<eaten-by}
Animal weight:integer <<disjoint>> eaten-by some [1..*] = AnimaClarnivore
and (eats some Animal) <<Label>> "Panthera leo"
Lion
= Animal Herbivore
and (eats only
(Plant
or (is-part-of only Plant)))
eats eaten-by
only some Giraffe
[1..*] Label("giraffa
camelopardalis")
Figure 1 depicts a variation of the popular African wildlife ontology [
The OWLGrEd’s annotation visualization framework allows mapping the built-in and user-defined annotation properties onto editor’s visual styles and behavior patterns, thus allowing customizable annotation assertion visualization.
An annotation assertion for an OWL entity (e.g. OWL class or OWL property) can be visualized in OWLGrEd either textually within the visual representation object for the entity (Inside mode, cf. Giraffe class label in Fig.1), or by a separate box connected to the box/line with entity representation (Outside mode, cf. Lion class label).
In order to determine the visualization mode for an annotation property, say P, we introduce a (visual) annotation property aShowMode in og namespace denoting http://owlgred.lumii.lv/2011/visual/1.0/, and annotate P itself with this property, as in AA(og:aShowMode :P og:modeInside)1. We introduce also annotation properties og:aClassShowMode and og:aPropertyShowMode to describe visual modes for Passertion visualization for subjects that are OWL classes and properties respectively.
The advanced annotation visualization framework allows adding specific visual
style and behavior annotations to aShowMode-assertions (cf. Fig. 2) that are
interpretted by OWLGrEd. The style/behavior annotations in the case of Inside showing mode
may set the visual style of the annotation P field (og:displayStyle-annotation)2 and of
the diagram element (box or line) containing the annotation field
(og:displayElemStyle). The style annotation value is a string with encoded values of style items
from visual style metamodel of [
The type of showing annotation’s assertions may be set by og:prSheetTypeannotation. Its value og:Text (the default) denotes using text field for representing the annotation value; og:Item denotes representing the annotation via placing its property name (URI) in a designated single-valued compartment (only one og:Item-type annotation can be shown visually for any subject).
The prefix/suffix for annotation assertion presentation in the diagram can be specified by og:displayValuePrefix and og:displayValueSuffix annotations. AA( AA(
A(og:prSheetType og:Item) A(og:displayElemStyle “bkgColor=’blue’”) og:aClassShowMode :ClassDB og:Inside) A(og:aDependency :ClassDB) A(og:displayStyle “picture=’db.jpg’”) og:aClassShowMode :DBExpr og:Inside)
Fig. 2. Visual annotation specification and application example A(og:aDependency :Q) annotation of P’s aShowMode-assertion states that the specified P visualization effects apply only to subjects that are annotated also by Q, and A(og:aDomainDependency :Q) states the dependence of P-assertion visualization features from its subject’s domain annotation by Q. Fig. 2 shows OWL class Person, with ClassDB and DBExpr annotations, before and after visual annotation application. 1 We let here and in the following examples A to stand for Annotation and AA for AnnotationAssertion 2 An inner-level og:compID-assertion may specify relation of visual properties to another compartment.
We note that A(og:prSheetType og:Item) annotations are sufficient to state that an annotation property (e.g. ClassDB) behaves like UML stereotype; og:aDependency provides visual framework for stereotype’s tagged values (e.g. a DBExpr-annotation is visualized in a field with database icon only for ClassDB-annotated classes). Let for Mini-University ontology (Fig.3) there be assertions AA(user:isComposition :includes “True”) and AA(user:isDerivedUnion :relates “True”) with user-defined annotation properties isComposition and isDerivedUnion that are used for encoding UML composition and property derived union constructs, not expressible in OWL. The following visual annotations allow creating typical UML representations for these constructs in OWLGrEd (cf. representation of :includes and :relates in Fig.3): AA( A(og:displayElemStyle “line_start=’diamond’”) og:aShowMode user:isComposition og:Inside) AA( A(A(og:compID “name”) og:displayValuePrefix “/”) A(og:displayStyle “visible=False”) og:aShowMode user:isDerivedUnion og:Inside)