Open book assessments are said to be assessments which give learners a free pass to course work, but what I've found is that it allows the students to make use of their knowledge and experience for different practical situations. 

Closed book assessments often get a bad reputation because not everyone has a good memory.

Observations are a creative way to assess knowledge and give an opportunity for students who know how to think oon their feet and those who may struggle to express themselves through written oor spoken works.

Portfolios are assumed to be irrelevant however, this is a good way to use Self-referenced learneing and to see the learner's progress over time.