Because of the rapid changes in the environment in which businesses operate, businesses have to become more flexible. The smart business network has emerged as a new organisational paradigm that promises more flexibility. A smart business network is a network of multiple actors that is supported by an open digital platform. Flexibility at the business level requires flexibility at the information technology level and alignment between the business level and the information technology level. The research described in the thesis focuses on the flexibility of the open digital platform at the information technology level. This open digital platform is the software system that supports the business processes of the actors of the smart business network. The objective is to design a flexible software system for a smart business network. The research is performed with an existing smart business network as the case study: the Internet Learning Community (IBLC). The thesis introduces an ontology-driven software architecture and a software engineering approach that is complementary to that architecture. The ontology-driven architecture is based upon the notion that the different actors in a smart business network may have different perceptions upon the business domain. An actor’s view upon the business domain is formalized in an ontology. The ontology consists of the terms and their relations used by the actor. The ontology is linked to the software components by models, which describe the individual components of the software system. The models and the source code of the components are defined using the same terms and relations as defined by the ontology.