Abstract. Executable schema mappings between XML schemas are essential to support numerous data management tasks such as data exchange, data integration and schema evolution. The novelty of this paper consists in a method for automatic generation of automappings (automorphisms) from key constraints and value dependencies over XML schemas, and designing algebraic operations on mappings and schemas represented by automappings. During execution of mappings some missing or incomplete data may be inferred. A well-defined executable semantics for mappings and operations on mappings are proposed. A mapping language XDMap to specify XML schema mappings is discussed. The language allows to specify executable mappings that can be used to compute target instances from source instances preserving key constraints and value dependencies. The significance of mappings and operators over mappings is discussed on a scenario of data exchange in a P2P setting.