1. A method of creating a requirement description for testing an embedded system, comprising: storing a vocabulary of natural-language, selectable text segments in a data processing system, each of said text segments being combinable only with a deterministically selected subset of said text segments to form at least one natural-language sentence including a condition and a response to a condition, and storing a requirements metamodel in the data processing system, each text segment being linked to an instance in the requirements metamodel such that when a text segment is selected a machine readable description of the text segment is created and such that said condition is assigned a value placeable at an input of the embedded system and the response to the condition is assigned a value placeable at an output of the embedded system.