CiTO v2.0 contains just two main object properties, cito:cites and its inverse cito:isCitedBy, each of which as thirty-two sub-properties. Intentionally, these properties are not constrained as to domain or range, thereby maximising their applicability in a wide range of citation contexts. Additionally, CiTO contains one additional generic object property, cito:shareAuthorsWith, that may be used even outside a citation context.
Some have criticised CiTO for having too many properties, making it confusing for potential users, and Martin Fenner chose to use only the ten ‘most popular’ properties in his CiTO plug-in for WordPress, previously mentioned in this blog post. In response, I would point out that each property has a distinct and clearly defined meaning, and that together they provide an appropriate level of expressivity for effective use. Nevertheless, it is clearly difficult to conceptualize all the CiTO properties at one time, if they are being viewed using an ontology editor such as Protégé. I have thus created the following figure that groups CiTO properties by similarity, in the hope that this will facilitate choice of the most appropriate one.
Clustering of CiTO relationships by similarity
As shown in the figure, the CiTO properties and sub-properties (and, consequently, their inverses) may be classified as rhetorical (upper oval) and/or factual (lower oval, dark blue text), with the rhetorical properties being grouped in three sets depending on their connotation: positive (green), neutral or informative (blue) and negative (red). Five properties (in purple, within the overlap of the ovals) have both factual and rhetorical characteristics. The inverse properties are not shown.