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2.1. Content Structure and the Activity Tree
A content structure diagram is a common tool used by the instructional design community to describe the hierarchical relationship of a learning experience. IMS SS defines and utilizes a similar concept called an Activity Tree to describe a structure of learning activities. The activity tree allows the SCORM SN model to describe informational and processing requirements such as sequencing algorithms and behaviors in an implementation independent manner. Figure 2.1a represents an example of an activity tree. The root of the activity tree is activity A – the root of an activity tree is also a learning activity as defined above and more specifically a cluster (in most cases).
Figure 2.1a: An Example of an Activity Tree
It is anticipated, but not required, that systems implementing sequencing will have an internal proprietary representation of the activity tree, which may or may not be a tree data structure. SCORM does not define when or how an activity tree is created within an LMS. In addition, SCORM does not require that an activity tree ever be a static structure. Implementations are free to dynamically alter the structure of an activity tree and the sequencing information applied to activities in the activity tree as they see fit, so long as the Sequencing Definition Model (refer to Section 3: The Sequencing Definition Model) and Sequencing Behaviors (refer to Section 4: Sequencing Behaviors) are adhered to. If an implementation chooses to dynamically modify an activity tree while a learner is interacting with content objects associated with its activities, it is recommended that the LMS does so in a manner that does not disrupt the current learner experience.
Again, it is not the intention of SCORM to mandate how authoring tools and LMSs implement activity trees, or how instructional design methodologies are to be modified to focus on an activity tree. Rather, an activity tree is a general term that represents an instance of hierarchical learning activities and the corresponding sequencing information for the interoperable application of specified sequencing behaviors.