XML documents and, more generally, semistructured data, can be seen as labelled graphs. In this paper we set a correspondence between such graphs and the models of a language of hybrid multimodal logic. This allows us to characterize a schema for semistructured data as a formula of hybrid multimodal logic, and instances of the schema (data graphs) as models of this formula. We also investigate how to express in such a logic integrity constraints on semistructured data, in particular some classes of constraints widely considered in the literature. The contribution of this work is twofold: 1) We generalize the notion of schema, by proposing a definition of schema were references are “well typed” (contrary to what happens with DTDs). 2) We formalize semistructured data, schema for semistructured data and integrity constraints in a unique framework, namely hybrid multimodal logic.