PreMOn overview

Semantic Classes and Roles

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At the core of the PreMOn Ontology are classes pmo:SemanticClass and pmo:SemanticRole. pmo:SemanticClass homogeneously represents the semantic classes from the various predicate models. That is, individuals of this class correspond to rolesets in PropBank and NomBank (e.g., pm:nb10-seller.01 and pm:pb17-sell.01), verb classes in VerbNet (e.g., pm:vn32-give-13.1-1), and frames in FrameNet (e.g., pm:fn15-commerce sell). An instance of pmo:SemanticClass typically has (via property pmo:semRole) a number of pmo:SemanticRoles, representing, from a semantic point of view, the roles the arguments of that pmo:SemanticClass can play.

Semantic roles are defined locally to semantic classes, so VerbNet agent is represented as multiple semantic roles, one for each verb class it occurs in, and with each semantic role linked to its specific selectional restrictions (if any). Note that pmo:SemanticClass is defined as subclass of ontolex:LexicalConcept, as we see pmo:SemanticClasses as essentially informal concepts rather than well defined concepts of a formal ontology (although an ontology can be derived from them, cf., FrameBase and ESO).

Properties pmo:classRel and pmo:roleRel, and their resource-specific subproperties, are introduced to express the relations between elements at each level, such as subtyping, and predicate and role inheritance (e.g., pmofn:inheritsFrom and pmofn:inheritsFromFER for FrameNet). Additional resource-specific classes (e.g., pmovn:ThematicRole) and properties (e.g., pmovn:thematicRole) further characterize important aspects of each predicate model, like commonalities between semantic roles.

Mappings

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Mappings between different predicate models are practically relevant but cannot be expressed using only the classes above, as they are often defined (e.g., in SemLink and PredicateMatrix) in terms of <pmo:SemanticClass, ontolex:LexicalEntry> pairs. To model these pairs, one could reuse the notion of ontolex:LexicalSense. However, its formalization in OntoLex-Lemon as reified relation depends on the existence of (exactly) one ontological entity for each <ontolex:LexicalConcept, ontolex:LexicalEntry> pair, a strong constraint that we do not necessarily need for our purposes. Therefore, we introduce the pmo:Conceptualization class. Structurally, a pmo:Conceptualization can be seen as the reification of the ontolex:evokes relation between ontolex:LexicalEntry and ontolex:LexicalConcept. Semantically, it can be seen as a very specific intensional concept (among many, in case of polysemy) evoked by a single ontolex:LexicalEntry, which can be generalized to a ontolex:LexicalConcept when multiple entries are considered but with a possible loss of information that prevents precise alignments to be represented.

Mappings are explicitly represented as individuals of class pmo:Mapping, and can be seen as sets of (or n-ary relations between) either (i) pmo:Conceptualizations, (ii) pmo:SemanticClasses, and (iii) pmo:SemanticRoles, with role mappings anchored to conceptualization or class mappings via property pmo:semRoleMapping. We rely on this set-like modeling, since mappings are not necessarily represented as binary relations in predicate mapping resources: e.g., in the PredicateMatrix, each row represents the mapping of a semantic role / lexical entry pair over the different resources (e.g., <13.1-1-agent, deal> in VerbNet, <sell.01-arg0, sell> in PropBank, <Commerce Sell-seller, sell> in FrameNet) as well as the corresponding WordNet verb sense. Reifying the n-ary mapping relation also allows us, if needed, to further characterize each single mapping, asserting additional information such as confidence and reliability. Moreover, it is possible to further specialize mappings (e.g., to model mappings holding only in one direction, from a resource to another one, or to represent different types of relationships among the members of the mapping) by subtyping the pmo:Mapping class or the property (pmo:item) relating a pmo:Mapping to its members.

Ontological Mappings

Building on OntoLex-Lemon, PreMOn inherits the capability of linking lexical content to ontological resources. In particular, being ontolex:LexicalConcepts, pmo:SemanticClasses inherit the link (via ontolex:isConceptOf) to the ontological entities formalizing them, typically event classes.

However, in order to properly align predicate models to existing frame/event-based ontologies such as FrameBase and ESO, PreMOn introduces the property pmo:ontologyMatch, having as domain SKOS Concept, to enable the possibility of linking to ontological entities also other resources than ontolex:LexicalConcepts. In particular, pmo:ontologyMatch property enables the alignment to ontology elements of resources such as:

• pmo:Conceptualizations
• pmo:SemanticClasses (in this case, ontolex:isConceptOf can be seen as a subproperty of pmo:ontologyMatch, although we abstained from formally enforcing this)
• pmo:SemanticRoles.

Annotations

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Predicate models are typically complemented by examples showing concrete occurrences of semantic classes and roles in text. More generally, a text can be annotated with semantic classes and roles as a result of manual or automatic SRL.

The PreMOn Ontology provides some common primitives, based on the NLP Interchange Format (NIF), which aim at properly modeling the heterogeneous annotations of a text for different predicate models. NIF introduces the general notion of nif:String to represent arbitrary text strings. nif:Context is a particular subclass of nif:String, representing a whole string of text. Any substring (itself a nif:String) has a nif:referenceContext relation to the nif:Context individual representing the whole text containing it.

To specifically model the aforementioned examples complementing predicate models, we introduce pmo:Example, subclass of nif:Context, to represent the string associated with the example. The occurrence of a ontolex:LexicalEntry, pmo:SemanticClass, or pmo:SemanticRole in a nif:Context is denoted by an instance of nif:Annotation, related to the given ontolex:LexicalEntry, pmo:SemanticClass, or pmo:SemanticRole via property pmo:valueObj (the value attached to the annotation), and to the nif:Context instance via property nif:annotation. If detailed information on the specific span of text (i.e., substring) denoting the ontolex:LexicalEntry, pmo:SemanticClass, or pmo:SemanticRole is available (e.g., FrameNet provides the specific offsets of lexical units, frames, and frame elements, in the example text) an additional instance of pmo:Markable, subclass of nif:String, is created and linked to the specific nif:Annotation and nif:Context via properties nif:annotation and nif:referenceContext, respectively. As the same nif:Context may contain multiple nif:Annotations referring to one or more semantic classes and their corresponding roles, an additional pmo:AnnotationSet instance is created to cluster annotations from the same predicate structure.

Below you can find an image illustrating the instantiation of the PreMOn Ontology with some semantic classes, semantic roles, mappings, and examples, with predicate model data.

Additional classes and properties are defined in the specific submodule for each predicate model (PropBank, NomBank, VerbNet, and FrameNet).