Class cohesion or degree of the relations of class members is considered as one of the crucial quality criteria. A class with a high cohesion improves understandability, maintainability and reusability. The class cohesion metrics can be measured quantitatively and therefore can be used as a base for assessing the quality of design. The main objective of this paper is to identify important research directions in the area of class cohesion metrics that require further attention in order to develop more effective and efficient class cohesion metrics for software engineering. In this paper, we discuss the class cohesion assessing metrics (thirty-two metrics) that have received the most attention in the research community and compare them from different aspects. We also present desirable properties of cohesion metrics to validate class cohesion metrics.