The LKIF Core Ontology is developed by the ESTRELLA consortium to cater for a continuing need for a standard vocabulary of basic legal terms when exchanging knowledge between different knowledge based systems. The ontology defines a set of approximately 200 concepts ranging from abstract to concrete which can be used to lay the groundwork for any legal knowledge based system.


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The LKIF Core ontology is available at



The LKIF core legal ontology consists of 15 modules, each of which describes a set of closely related concepts from both legal and commonsense domains. In that sense, the LKIF core ontology is rather a library of ontologies relevant for the legal domain than a monolithic body of definitions.

The most abstract concepts are defined in five closely related modules: top, place, mereology, time and spacetime.

  • top The LKIF top ontology is largely based on the top-level of LRI-Core but has less ontological commitment in the sense that it imposes less restrictions on subclasses of the top categories.
  • place The place module partially implements the theory of relative places (Donnelly, 2005) in OWL DL.
  • mereology The mereology module defines mereological concepts such as parts and wholes, and typical mereological relations such as part of, component of, containment, membership etc.
  • time The time module provides an OWL DL implementation of the theory of time by Allen (1984).
  • spacetime The space-time module is a placeholder for the place and time modules.

Basic-level concepts are distributed across four modules: process, role, action and expression.

  • process The process module extends the LKIF top ontology module with a definition of changes, processes (being causal changes) and physical objects. It introduces a limited set of properties for describing participant roles of processes.
  • role The role module defines a typology of roles (epistemic roles, functions, person roles, organisation roles) and the plays-property for relating a role filler to a role.
  • action The action module describes the vocabulary for representing actions in general. Actions are processes which are performed by some agent (the actor of the action). This module does not commit itself to a particular theory on thematic roles.
  • expression The expression module describes a vocabulary for describing, propositions and propositional attitudes (belief, intention), qualifications, statements and media. It furthermore extends the role module with a number or epistemic roles, and is the basis for the definition of norms.

These basic clusters are extended by three modules that form the legal ontology: legal action, legal role and norm.

  • legal-action The legal action module extends the action module with a number of legal concepts related to action and agent, such as public acts, public bodies, legal person, natural person etc.
  • legal-role The legal role module extends the role module with a small number of legal concepts related to roles, legal professions etc.
  • norm The norm module is an extension primarily on the expression module where norms are defined as qualifications. Please refer to Deliverable 1.1 for a more in-depth description of the underlying theory. It furthermore defines a number of legal sources, e.g. legal documents, customary law etc., and a typology of rights and powers, cf. Sartor (2006), Rubino et al. (2006)

In addition to these legal clusters, two modules are provided that cover the basic vocabulary of two frameworks: modification and rules.

  • modification The modification module is both an extension of the time module and the legal action module. The time module is extended with numerous intervals and moments describing the efficacy and being in force of legal documents. The action module is extended with a typology of modifications. These concepts are described in further detail in Deliverable 3.2 of the ESTRELLA project.
  • rules The rules & argumentation module defines roles central to argumentation, and describes the vocabulary for LKIF rules as defined in Deliverable 1.1, chapter 5. The module leaves room for further extension to complex argumentation frameworks (AIF, Carneades).

Finally, these fourteen modules are integrated in the LKIF-Core ontology module. This module does not provide any additional definitions, but functions as an entry-point for users of the ontology library.