A concept map is a diagram showing the relationships among concepts. They are graphical tools for organizing and representing knowledge. Concepts, usually represented as boxes or circles, are connected with labeled arrows in a downward-branching hierarchical structure. The relationship between concepts can be articulated in linking phrases such as "gives rise to", "results in", "is required by," or "contributes to". The technique for visualizing these relationships among different concepts is called "Concept mapping". An industry standard that implements formal rules for designing at least a subset of such diagrams is the Unified Modeling Language (UML).