How you can define the strength and weakness of your employee profomence?

The strength and weakness of an employee performance can be based on the specific duties and responsibilities for the job.  The strength and weakness can be gleaned from her accomplishments, output, contributions and interpersonal relations. 

There should be a job description for each job & employee determined by HR, according to that the direct manager should set a KPIs to measure the performance. Training & good coaching definitely will increase the job knowledge & satisfaction resulting in excellent performance.