JOB DESCRIPTIONS: TASK-BASED, RESULTS-BASED OR COMPETENCY-BASED?

Many of the job descriptions we encounter in our client businesses are task-based. They ignore the fact that results, not activities, are what add value to the business. Also, activities-based job descriptions tend to box employees into particular roles or focus them on particular subset of actions; this type of job description can contribute to the famous "it’s not my job" attitude. And if job descriptions form the basis for performance measurement, this approach will further de-link organization objectives and results from individual and team performance. So, what are some alternatives to task/activity based job descriptions?