What is the difference between a strength, a competitive advantage, and a sustainable competitive advantage? What makes an ability (or set of abilities) a core competency?

Management question

1. What is the difference between a strength, a competitive advantage, and a sustainable competitive advantage?
2. What makes an ability (or set of abilities) a core competency?
3. Why is it necessary to perform an external and internal analysis before the firm can identify its true core competencies?
4. Pick a company you are familiar with. Can you identify some of its core competencies?
5. How is the idea of strategic intent different from models of strategy that emphasize achieving a fit between the firm’s strategies and its current strengths, weaknesses, opportunities, and threats (SWOT)?
6. Can a strategic intent be too ambitious?