One general challenge that comes with the strict separation of design time (authoring) and runtime (execution) in IMS LD is the insecurity during authoring about how the designed unit of learning will look like in the VLE during execution, which was previously pointed out as a major problem by Neumann and colleagues (2010).
Then, one after the other, each unit of learning was played in the SLeD player.
Learners in these units of learning could only identify a chance for student-student interaction if they received explicit instructions in the activity, and if the author of the unit of learning included corresponding services where the interaction takes place, such as a chat or forum.
During the course of the unit of learning, the team members chose a team leader, who was then assigned this additional role.
For illustration, see the screenshots below (Figure 2 and Figure 3), which were taken from the DECONSTRUCTIVISM unit of learning. As the two navigation trees indicate, there was no guidance for learners or teachers regarding when the teacher was to support the students during their activities.
The SLeD player interprets IMS LD units of learning in a way that learners and teachers are presented with separate views onto the (same) unit of learning. Each role receives own activities with own instructions and is not aware of other roles and their activities.
Such resources or tools are sometimes external to the unit of learning, for example, external webpages.
In the unit of learning SKYSCRAPERS AND RESIDENTIAL HOMES--LEVEL A, the nested activity structures are confusing and do not support navigational orientation.
A service element in an IMS LD unit of learning is an abstract declaration of the required facility or tool, for example, a synchronous conferencing service.
SCORM uses the IMS content packaging specification as a means for incorporating its various components: assets, SCOs, activities, content organisation, and metadata within a single content aggregation (or unit of learning).
SCORM does not prescribe the actual size of a SCO or even the size of a whole content aggregation (or unit of learning).