Performance appraisal is a process used for some firms in order to evaluate the employees' efficiency and productivity for planning their promotion policy. Initially this process was carried out just by the executive staff, but recently it has evolved to an evaluation process based on the opinion of different reviewers, supervisors, collaborators, clients and the employee himself (360-degree method). In such a evaluation process the reviewers evaluate some indicators related to the employee performance appraisal. The sets of Reviewers involve in the evaluation process might have different degree of knowledge about the evaluated employee. It then seems suitable to offer a flexible framework in which different reviewers can express their assessments in different domains according to their knowledge, i.e., an heterogeneous evaluation framework. The final aim is to design an performance appraisal model in such a framework that computes a final evaluation for each employee. That will be used by the management team to make their decisions regarding their incentive and promotion policy.