TRIZ (the Russian acronym for Theory of Resolution of Inventive Problems) is a methodology to guide the search for inventive solutions to one, or a few, difficult problems. Classic TRIZ is not well suited to the examination of complex situations composed of many problems, sub-problems and partial solutions, strongly interconnected. It has therefore been completed to give birth, among others, to the Inventive Design Methodology (IDM) framework.TRIZ and IDM share many similarities with Artificial Intelligence methods: they both propose to solve a problem by reformulation in an abstract model. Generic solving patterns are applied to this abstract model to produce abstract solutions. The domain-specific knowledge is then used to get the final solution concept. However, neither TRIZ nor IDM's descriptions are formal enough to permit a reliable software implementation and rely mainly on the experts' manual work. Therefore this paper proposes an ontological formalization of TRIZ and IDM to overcome these difficulties and allow the development of software tools to assist TRIZ/IDM experts in their work.