Abstract : The Object Management Group (OMG) Unified Modeling Manguage (UML) profile for Modeling and Analysis of Real-Time and Embedded systems (MARTE) aims at using the general-purpose modeling language UML in the domain of Real-Time and Embedded (RTE) systems. To achieve this goal, it is absolutely required to introduce inside the mainly untimed UML an unambiguous time structure which MARTE model elements can rely on to build precise models amenable to formal analysis. The MARTE Time model has defined such a structure. We have also defined a non-normative concrete syntax called the Clock Constraint Specification Language (CCSL) to demonstrate what can be done based on this structure. This paper gives a brief overview of this syntax and its formal semantics, and shows how existing UML model elements can be used to apply this syntax in a graphical way and benefit from the semantics.