There is much interest in building ontologies, however, there are few works pointing to a large-scale use of ontologies. Some reasons for this are time, cost, and resources associated with the development. With the goal of reducing such efforts, ontology learning methods have been developed. Therefore, it is necessary to automate the process of acquiring knowledge and different approaches have been suggested. The use of texts as a source of knowledge acquisition appears to be a correct path, since language is the first manner of knowledge transferring among human beings. Besides, there are a lot of digital documents available. To support semi-automatic construction of ontologies from texts, several tools have been developed, each one using different techniques and methods. Due to the importance of using these tools, this paper describes the available tools, their main features, and usability from the perspective of a regular user.
Knowledge representation; Ontology; Ontology learning
