In classifying cognitive analysis methods, some researchers (e.g., Cooke, 1994) present most of the methods under knowledge analysis, while others (Royer, Cisero, and Carlo, 1993) include most under skill analysis. In some contexts, knowledge can be closely linked with skill, while in others, skills are closely linked with, and sometimes considered part of, knowledge. This ambiguity between knowledge and skill is not necessary in operational environments. The distinction between declarative and procedural knowledge helps to differentiate between knowledge and skills. This book refers to Declarative knowledge as just knowledge, which is associated with flexible performance and helps predict what the outcome will be. This book refers to Procedural knowledge as skill, because of its tight link with efficient performance (Anderson, 1993).