To simplify the design of adaptive hypermedia systems, various frameworks have been developed.
2.2.1 AHAM
The AHAM model [29], [30] extends the Dexter hypermedia model [31] to describe adaptation. The Dexter model contains a ‘Runtime layer’, a ‘Storage layer’ and a ‘Within Component layer’. AHAM extends this principle through the definition of the following three models.
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The ‘domain model’ is used to store fragments of information, and describes how these fragments are structured. Specifically, the domain model
contains ‘concepts’ (representing the subject), with each concept containing a number of attributes.
The ‘user model’ stores information about the user, by defining an overlay model. This means that the user model can separately address each concept, thereby storing properties that describe the user’s knowledge of the concept. Moreover, the user model can store other properties that link the user to the concept, such as a property that denotes the concept has been read.
The ‘adaptation model’ [32] (previously known as the ‘teaching model’[30]) describes how the relationships between the concepts (from the domain model) should be interpreted to form pedagogical relationships that interact with the user model and can therefore be used to guide the user around the course.
2.2.2 Generic Adaptivity Model (GAM)
GAM [33] was created to provide a more generic abstraction of AHAM. Specifically, it removes the dependence on hypermedia and expresses the process of adaptation as a state-machine. The model consists of a ‘domain model’, ‘adaptation model’ and ‘user model’, which are all similar to that used by AHAM. One of the main
differences between GAM and AHAM is that since GAM is not specifically used within hypertext, the structure of the domain is not specified in terms of concepts. Moreover, the domain model only specifies the usage of attributes, and leaves the
9 actual structure of the domain model to the designer of the system. Similarly, GAM introduces an ‘interface model’ which defines the possible events that can be triggered by the user, and how such events might affect the adaptation model. 2.2.3 Munich Reference Model
The Munich Reference Model [34] uses UML to specify three separate meta- models; the ‘domain meta-model’, the ‘adaptation meta-model’, and the ‘user meta-model’. Like AHAM, the Munich model’s meta-models all occur within the ‘Storage Layer’ of the Dexter hypermedia model. Each model performs a similar role to its namesake from AHAM, yet the Munich model’s specification focuses on a more formal object-oriented approach.
2.2.4 LAOS Model
The LAOS model [35] is based around the AHAM model, and consists of five
separate layers. It is designed to reduce the complexity of the authoring process by allowing the author to focus their attention on the design of each individual layer, rather than being concerned with authoring the entire content and adaptation specification in one process. LAOS therefore adheres to the ‘Separation of Concerns’ principle, described in Section 2.9.1 .
Figure 2.1 (previously published in [35]) shows the relationship between the five models of the LAOS model.
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Figure 2.1: The five layer LAOS model
A description of each individual layer is provided below.
Domain model (DM): Similar to the domain model in AHAM, the Domain layer contains the information content in the form of concepts and
attributes. The domain model also defines how the information is structured (but contains no pedagogical information). Although the domain model stores relationships that define the structure of the content, the domain model does not define the order in which the content should be studied (unlike the domain model in AHAM). In the implementations of the LAOS domain model within MOT, an example of a domain model concept would
11 be a topic such as ‘Computer’, whilst an attribute could be ‘introduction’ containing some hypertext introducing the topic.
Goal and Constraints model (GM): The goal model references concept attributes within the domain model so that pedagogical metadata can be defined about each concept. The goal model also stores information about the order and structure of the content. This allows different authors to produce goal maps that use the same domain but order/structure the content in a different way. In the implementations of the LAOS goal model within MOT, authors can add labels and weights to sublessons to represent when the corresponding content should be delivered. For instance, the sublesson corresponding to the ‘introduction’ domain attribute could be labelled ‘beginner’ so that it can be delivered to beginner users (see Section 2.6.2).
User model (UM):As with AHAM, the user model contains an overlay of the goal model, therefore allowing the storage of information that relates the user to each individual concept. For instance, an implementation of LAOS would be able to store a user’s characteristics to label the user as ‘beginner’.
Adaptation model (AM): As with AHAM, the adaptation model contains the code that determines how the course will adapt to the needs of the user. Within LAOS, the adaptation is usually specified in the form of a LAG strategy[36].
Presentation model (PM): The presentation model contains information about how the content is delivered, allowing the content to be assembled
12 into a form that can be interpreted by the browser (usually using HTML). In more recent implementations (described in Chapter 10), the presentation model has also been used to adaptively change the screen layout.
2.2.5 Concept Adaptation Model (CAM)
The Concept Adaptation Model (CAM) [37] was developed as part of the GRAPPLE project [38], and inherits features from both the AHAM and LAOS models.
Adaptation is specified using Concept Relationship Types (CRTs). Like both AHAM and LAOS, there is a domain model and a user model. However, rather than specifying adaptation within a single layer, CAM allows adaptation to be spread between multiple layers. The implementation of the CAM within the GRAPPLE project is described in Chapter 8 .