This half-day event is the fourth workshop in the series on Definitions in Ontologies. The first three such workshops (DO 2013, IWOOD 2014, and IWOOD 2015) were held in conjunction with ICBO 2013, ICBO 2014, and ICBO 2015. This fourth workshop will be held in conjunction with ICBO 2016 at Oregon State University in Corvallis, Oregon, from August 1 to 4, 2016. The 2016 edition is focused on definition writing, evaluation, revision strategies, methodologies, and tools.

Definitions of terms in ontologies serve a number of purposes. For example, logical definitions allow reasoners to assist in and verify classification, lessening the development burden and enabling expressive query. Natural language definitions can help ameliorate low inter-annotator agreement. Good definitions allow for non-experts and experts in adjacent disciplines to understand unfamiliar terms making it possible to confidently use terms from external ontologies, facilitating data integration.

Despite the importance of definitions in ontologies, developers often have little if any training in writing definitions and axioms, as shown in Selja Seppälä and Alan Ruttenberg, Survey on defining practices in ontologies: Report, July 2013. This leads to varying definition practices and inconsistent definition quality. Worse, textual and logical definitions are often left out of ontologies altogether.

The goals of this workshop are:

• to engage participants in discussing what are well-constructed textual and logical definitions; 
• to disseminate methodological solutions to textual and logical definition writing and generation; 
• to introduce tools to assist in definition creation; 
• to bring together interested researchers and developers to explore issues relating to definitions and enable cross-fertilization leading to new approaches; 
• to share case studies that expose difficulties arising in definition construction, evaluation, interpretation, and revision; 
• to disseminate strategies of evaluation of definitions by readers from different domains in order to reveal potential difficulties in interpretation; 
• to disseminate practices for participants to bring back to their projects that will improve the quality of their ontologies; 
• to provide an opportunity for interaction and collaboration with experts on definitional practices; 
• to provide a platform for ontology developers to initiate cross-ontology collaborations for definition-related matters.