How to determine the correct structure of employee competencies?

Summary:

We are currently implementing PRM (Project Resource Management) for one of our client and we want to have the competencies available for the employee so that we can use them as a criteria in requesting resources for their respective projects.

Our concern is how do we determine the structure of the competencies? How do we know if the skill of an employee is a competency? What's the difference between the two?

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