1. In a processing system a method comprising: receiving measurement data; processing the measurement data to create or update at least two models and one or more characteristics associated with each model based on the measurement data, where each of the models is a representation of a real-world thing; processing the characteristics associated with the models to form one or more relationships between the models when the characteristics are such that two or more of the models are regarded as being related according to one or more relationship criteria; processing the relationships to generate one or more alerts when one or more of the relationships meet one or more alert criteria.