This paper addresses issues in visual language the-ory with the help of logic formalisms that were de-veloped for reasoning tasks by the artificial intelli-gence and spatial databases community, especially for spatial and diagrammatical reasoning. We de-scribe an approach based on three formal compo-nents. Topology is used to define basic geometric objects. Theory about spatial relations from the ... [Show full abstract] domain of spatial databases is employed to define possible relationships between visual language ele-ments. Description logic theory from the AI com-munity is used to combine topology and spatial relations. The resulting theory has been success-fully applied to formally specifying semantics of vi-sual languages. The theory's application is illus-trated with a specification of entity-relationship di-agrams.