[xwiki-users] A custom Map as class parameter

Hi All, actually i use a multi-select user-list as parameter on a class for all objects-instances. Now in need to add a value to any selected user which is in the list in the object. You have any idea how i can solve that in a good way? Example: Class: Skill Object 1: Skill A User-Selection in Object 1: User X, User Y Object 2: Skill B User-Selection in Object 2: User X, User Z Now i need the competence-level for every user on every skill, so i need something like User-Selection in Object WITH level: User X (Level 2), User Y (Level 3) This information is by definition in a Matrix, so somewhere i need to attach it. Maybe i need to create a custom class and use there user and skill. What do you think? Can you help me? Regards, Matthias