Representation model

Text layer

This is the textual content from which knowledge is extracted. It consists of ks:Resources (i.e., documents) identified by URIs. Each resource consists of a raw text and an accompanying RDF description rooted at the resource URI, including metadata attributes such as dct:title and dct:created.

Mention layer

This layer consists of ks:Mentions. Different types of mentions are defined in PIKES model. ks:InstanceMentions denote instances of the domain of discourse and are further specialized based on the type of instance: ks:FrameMention for frame instances; ks:NameMention for named instances; ks:TimeMention for time intervals; and ks:AttributeMention for instances in the value space of lexical attributes (e.g., ‘very strong’). ks:ParticipationMentions link argument instances to participated frame instances (e.g., ‘fight of HIV’ links argument ‘HIV’ to frame ‘fight’). ks:CoreferenceMentions comprise spans of text having the same referent.

Instance layer

The instance layer describes the things of interest contained in a textual resource, abstracting from the actual ways they are expressed in the text. The main objects are ks:Instances of persons, organizations, locations, frames, dates and other entities of the domain of discourse. Instances are typed with respect to various taxonomies, are enriched with textual properties (e.g., rdfs:label and foaf:name), and are linked by a number of relations, including owl:sameAs assertions triggered by ks:CoreferenceMentions and frame-argument participation assertions triggered by ks:ParticipationMentions where the property conveys the role played by the argument. In this representation, frame instances reify complex relationships and are the main vehicle for relating instances.

Inter-layer relations

Mention and Text layers are related by ks:mentionOf that links a ks:Mention to the ks:Resource it belongs to. Mention and Instance layers are related by three properties: ks:denotes, ks:implies, and ks:expresses:

• ks:denotes links a ks:InstanceMention to the ks:Instance it denotes.
• ks:implies links a ks:FrameMention to another instance (besides the denoted one) whose existence is implied by that mention, a situation occurring in case of argument nominalization.
• ks:expresses links a ks:Mention to the Instance layer assertions it expresses (i.e., that can be derived from it). Its RDF representation makes use of named graphs: each assertion of the Instance layer is placed in a named graph that represents the set of mentions (in some cases a single mention) that ks:expresses that particular assertion; ks:expresses is then asserted between each mention URI and the graph URI.

Put together, properties ks:denotes, ks:implies and ks:expresses allow any instance and assertion in the Instance layer to be always referred to the mention(s) from where it was derived, thus enabling a fine grained tracking of the specific piece of text from where a bit of knowledge was extracted.

PIKES and the KnowledgeStore

PIKES representation model is compliant with (and represents a specialization of) the KnowledgeStore data model (see KnowledgeStore core data model, meaning that the input and output consumed and produced by PIKES can be used to populate a KnowledgeStore instance, where all the content processed and produced can be accessed, navigated, and queried in an integrated fashion.