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It is important to note that there is a tension
between reusability and scalability, on one hand;
and flexibility and expressivity on the other. In
Sequencing Graphs, edges are only allowed inside
a container node or as an exit edge (i.e. to the
parent node). This permits that a graph is reused
easily, but it means that some activities cannot be
connected. However, allowing any node to connect
to any node can result in an unmanageable graph
when the number of activities is large. We think
that scalability and reusability are very important
goals, and thus consider that restricting edges and
cycles to the scope of a container node —whose
size is as big as the designer can handle, and not
more— is a reasonable compromise between
flexibility, reusability, and scalability.
Sequencing Graphs are a flexible technique
to describe adaptive sequencings. Positive results
from their application to the design and implemen-
tation of intelligent tutoring systems have been
presented and discussed in (Gutierrez et al., 2004;
Prieto-Linillos et al., 2006). In the next section we
will investigate the possibility of expressing SG in
terms of the IMS Learning Design specification.
Learning Design semantics. Additional details
about the process and the implementation of the
application can be found in (Gutierrez-Santos et
al., 2008). A brief note is made at the end of this
section about the relationship between Sequencing
Graphs (henceforth SG) and other specifications,
in particular IMS Simple Sequencing.
For the remainder of this chapter, we will
refer to entities of SG and IMS-LD. We will use
their XML tags to identify them. In the case of
SG, <sg:exercise> denotes a node associated to
a learning resource or activity, <sg:node> cor-
responds to a container node, and other tags are
usually self-explanatory (e.g. <sg:condition>). In
the case of IMS-LD, a complete description of
the XML language can be found in (IMS, 2003c).
Brief Description of IMS-LD
IMS Learning Design is not designed specifically
for addressing the sequencing problem. However,
it provides some tools that can be applied: prop-
erties, conditions and actions. These tools make
it possible to use IMS-LD elements to express
sequencings that have been defined with SG.
IMS-LD implements a vocabulary with plays,
acts, roles, activities and conditions that “is de-
signed to enable many different pedagogies to
be expressed” (IMS, 2003b), cf. (Koper, 2005).
Acts are included into plays, and are means to
synchronize different activities that occur simul-
taneously. Activities are performed by different
persons playing different roles. Roles are to be
instantiated by real people, and are grouped into
two built-in role families: student roles and teacher
roles. Finally, conditions (if something happens,
then this happens, else this other thing happens)
allow for variability in the course of the play.
Additionally, Learning Design allows the
definition and use of properties to store informa-
tion about the learning process. The overall entity
including the definition of a pedagogical strategy
or learning design, along with the resources or
REUSE OF ADAPTIVE
SEQUENCING WITH IMS-LD
There is a big effort in the elearning community for
the standardization of elearning processes. There
are two initiatives that are especially relevant for
the sequencing problem: IMS Simple Sequenc-
ing (IMS-SS) (IMS, 2003d) and IMS Learning
Design (IMS-LD) (IMS, 2003a). Both have the
support of many companies and research centers
and lots of efforts are concentrating around them,
especially on the latter. Creating material following
the IMS specification ensures that this material
can be played in any IMS-compliant system, and
the number grows every day.
This section describes therefore the main
aspects of the process that translates from the
semantics of Sequencing Graphs into IMS
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