Michael Porter has described a category scheme consisting of three general types of strategies that are commonly used by businesses to achieve and maintain competitive advantage. These three generic strategies are defined along two dimensions: strategic scope and strategic strength. Strategic scope is a demand-side dimension and looks at the size and composition of the market you intend to target. Strategic strength is a supply-side dimension and looks at the strength or core competency of the firm. In particular he identified two competencies that he felt were most important: product differentiation and product cost. He originally ranked each of the three dimensions as either low, medium, or high, and juxtaposed them in a three-dimensional matrix. That is, the category scheme was displayed as a 3 by 3 by 3 cube. But most of the 27 combinations were not viable. In his 1980 classic Competitive Strategy: Techniques for Analyzing Industries and Competitors, Porter simplifies the scheme by reducing it down to the three best strategies. They are cost leadership, differentiation, and market segmentation. Market segmentation is narrow in scope while both cost leadership and differentiation are relatively broad in market scope.