Internal class- (and object-) structure of the tract-tracing experiment view. A: UML class diagram showing all views involved in the definition of the 'tract-tracing-experiment', 'tract-tracing-histology' and 'tract-tracing-injection' views. Attribute notation based on Object Management Group (OMG) standards and is an internal representation of the VPDMf system. B: Screenshot showing the primitive-instance graph of an non-instantiated tract-tracing-experiment. This shows the potential complexity of each transaction with the underlying relational database system.