SN models the required behaviors and functionality that SCORM conformant LMSs must implement to process sequencing information at run-time. 

Describes the branching and flow of learning activities in terms of an Activity Tree, based on the results of a learner’s interactions with content objects and an authored sequencing strategy. 

An Activity Tree is a conceptual structure of learning activities managed by the LMS for each learner.  In SCORM, a learning activity may reference content objects that are delivered to the learner.