The two main directions in literature review in the agile literature review approach

The two main directions in literature review in the agile literature review approach: (I) the upward literature review direction and (II) the horizontal literature review direction.

(I) The upward literature review direction:

This refers to the effort to evaluate to what extent and how your chosen academic ideas will intellectually support the research task to which your chosen academic ideas belong.

(II) the horizontal literature review direction:

This refers to the effort to evaluate the relatedness, complementarity and incompatibility of the academic ideas you have chosen to inform the endeavor of the upward literature review.

For vertical literature review, academic journal articles are more useful than textbooks. As to horizontal literature review, textbooks are more relevant for the review exercise.