January 2012 Volume 15 Number 1 - Educational Technology ...

Figure 1 schematically depicts an illustrative example of program-markup language interactions in accordance with
the framework, indicating how multiple-layered semantic Web technologies are adopted.
Example 1. Consider the concrete example given in Figure 1. Where E is a set of learning objects and X is a set of
metadata coded with LOM. The software program ontology, K, is developed based on OWL and the logic program,
RuleML (RuleML 2002), is taken for R.
Definition 2. (Learning Object) A learning object LO∈E is a tuple LO=, where
Rid denotes an unique learning object identifier, such as URI.
Uid denotes an unique identifier of learning object owner.
ALO denotes a list of learning object attributes.
Learning objects are Web-accessible entities, such as web pages, pictures, programs, audio, video, etc. They are
distributed in the Internet and are identified by URI.
Definition 3. (LOM Document) A LOM-based metadata document of a learning object is a tuple LOMD=< LO, Ca,
Re, Oth>, where
LO denotes a learning object.
Ca denotes a classification metadata that describes the meanings or abstract concepts of learning objects.
Re denotes a relation metadata that describes the meanings or abstract concepts of relationship between learning
objects.
Oth denotes the other metadata in the LOM-based metadata document.
The LOM Information Model is broken up into nine categories. These categories are based on the definitions found
in the LOM Information Model. The nine categories of metadata elements are: General category, Life Cycle
category, Meta-metadata category, Technical category, Educational category, Rights category, Relation category,
Annotation category, and Classification category. This study only focuses on Classification category and Relation
category. The Classification category can be used to describe where the learning object falls within a particular
classification system. The Relation category can be used to describe features that define the relationship between this
learning object and other targeted learning objects. Each relationship is an outbound link that associates exactly two
learning objects, one local and one remote, with an arc going from the former to the latter.
Definition 4. (Ontology) A web-based ontology O∈K is a tuple O = , where
C denotes a set of concepts representing classes in an ontology.
P denotes a set of relations representation properties in an ontology.
α denotes the hierarchical relation function for classes. α: C → C, where
α(c1) = c2 means that c1 is a subclass of c2.
This hierarchical relation can be used to determine if two classes have subclass/superclass relationship
(Guarino and Welty 2004).
β denotes the hierarchical relation function for properties. β: P → P, where
β(p1) = p2 means that p1 is a sub-property of p2.
γ denotes the attribute relation function between classes. γ: P → C x C, where
γ(p1) = (c1 , c2) means that domain of p1 is c1 and range of p1 is c2.
Σ denotes a set of ontology axioms, expressed in an appropriate description logic.
Π denotes a set of RDF-based ontology language, such as RDF schema, DAML+OIL, or OWL.
An ontology is commonly defined as an explicit, formal specification of a shared conceptualization of a domain of
interest (Studer, Benjamins et al. 1998). It describes some application-relevant part of the world in a machine
understandable way. The reasoning capabilities of OWL will be discussed in the next section.
Definition 5. (Semantic Mapping Mechanism) A semantic mapping mechanism is a tuple SMM=< LOMD, LLO,
RLO, C,Λ, P, Υ>, where
LOMD denotes a learning object metadata document (as defined in Definition 3).
LLO denotes a local learning object that is mainly described by the LOMD.
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