Abstract: A user input interpreter (2) for interpreting user input to enable a user to provide a data processor (3) with a user command for controlling an operation to be carried out on an object presented to the user by a user interface of the data processor has: a data model provider (14) providing a data model (17) having object and operation data entry locations required to be populated in accordance with user input data to enable a user command to be generated for causing the data processor to carry out an operation on an object, each data entry location being associated with semantic identifier specifying means specifying a semantic identifier required to be associated with received user input data for that data entry location to be populated; a semantic meaning determiner (81, 82) for associating received user input data with semantic identifiers in accordance with semantic rules stored in the semantic rules store (11) to provide semantically identified user input data; and a data model populater (9) for populat