To develop or to improve a system requires to specify very early the user waits and the requirements which this system will have to answer throughout its life. So, languages of representation and mechanisms of validation and of check are necessary to describe and manage the reality complexity then to ensure the resultant system performs well its role and reach its objectives with a minimum level of risk. The concept of property is so often evoked. This article proposes a model allowing the representation and the manipulation of property concept as well as a reference repository of properties.