Adaptive Hypermedia Models and Frameworks

For the most parts of the birth of e-commerce, a major criticism of early e-commerce sites was that they offered too many links, making it difficult for users to ascertain which links will enable them to meet their needs [44]. The introduction of adaptive hypermedia is therefore seen by Garlatti and Kervella [64] as a solution to this situation, where users otherwise would get lost in hyperspace. Goodman and Litman [71] explained that, with adaptive hypermedia, links and contents that are relevant to the needs of users are provided. As a way of introducing adaptive hypermedia platforms, various adaptive hypermedia models are proposed. These models cover many areas in hypermedia – in particular education, although there are a few that cover advertising. However, all of them suffer from some limitation to produce adaptive systems that, for example, can support easy integration into websites, social interaction, the lightweight concept, and so on. The following subsection details the most well-known and effective models and frameworks for adaptive hypermedia.

3.4.1.Adaptive Hypermedia Application Model (AHAM)

AHAM [53, 144] is a Dexter-base reference model [53]. As such, AHAM focuses on the information nodes together with the link structures that connect those nodes. AHAM consists of three major elements, which are domain model, user model, and adaptation model [33].

The domain model is a major structural component of AHAM. In this model, the components used in the Adaptive hypermedia system are categorised in concepts and their relationships. The concept represents a summary of information from the application domain and can be atomic or composite [30]. The most used concept relationship is the type link, which is similar to the link component in the Dexter model. In AHAM, the prerequisite is an important type of concept relationship. When a concept C1 is a prerequisite to C2, then the user should first read C1 in order to read C2. It thus shows that for a user to understand C2 there is various information that they need to acquire by first reading C1 [33].

The user model in AHAM stores information as an overlay model on the domain model, and as free variables. For the former, the user model is characterised by many attributes that help to explain the manner in which the user is related to the concept. The user model may keep information about the

28 nature of the information acquired about a concept, or whether those concepts have any relevance to the user.

The adaptation model of AHAM is a set of rules covering both generic and specific adaptation [144]. The rules guide the process of adaptation and form the basis on which the Dexter model connects to the user model, and the presentation that is to be generated [110]. In specific adaptations the rules are always stated by the author.

While the AHAM model is one of the earliest and most effective means of creating adaptive hypermedia systems, it is not without some limitations. For example, the contents in the domain model are concepts or composite concepts and cannot describe any related elements that are not a concept. In addition, the structure of the user model is a rigid table-style structure that is unable to easily manipulate private and public information. Finally, this model, although claimed to be generic, is designed mainly for adaptation in the field of education, making its structure less suitable for advertising adaptation. For instance, the user model structure needs further components, to reflect a user’s social interaction. In addition, the adaptation model and the domain model should be simple for authors, to be created easily. Moreover, the adaptation model needs to be related to specific user characteristics, which are required for adaptive advertising, such as age and gender.

3.4.2.LAOS

LAOS [50] is a theoretical framework for authoring adaptive hypermedia systems that attempts to resolve the issue of concealed adaptation information. LAOS is a universal representation of a layered model for generic authoring of adaptive hypermedia [43]. Cristea [44] states that functionality and semantics guide the separation of adaptive hypermedia components into layers, in order to group the components based on their potential usage, mainly for later use and reuse. In short, the LAOS framework is made up of the following layers [44, 50, 127], as illustrated in Figure 5.1.

 The Domain Model (DM). Expresses the conceptual model and consists of sub-layers comprising atomic and composite concepts, each of which have their own respective attributes. The model contains concept maps with linked concepts to represent resources in addition to their characteristics.

29  Goal and constraints Model (GM). Goals provide a well-focused presentation, while constraints seek to limit the search space, in order to achieve a focused orientation of the material. This model sorts and regroups the domain model with regard to a specific goal. In addition, it allows for ordering and ‘AND/OR’ style relationships between attributes, and the actual analysis is conducted in the adaptation model.

 User Model (UM). As with the user model in AHAM, which is an overlay of the DM, the user model in LAOS is also an overlay of the goal model. Therefore, different user information can be assigned to different concepts, based on user experience.

 Adaptation Model (AM). The adaptation model is the layer containing the specification of the adaptive behaviour of the online system. It allows for various granularity representations of adaptation, starting from simple IF-THEN rules, triggered, e.g., when an event occurs, such as accessing a page, all the way to full adaptation strategies, that could, in the learning domain, correspond to a specific pedagogical strategy.

 Presentation Model (PM). The presentation model stores metadata on the presentation options, and drives the final presentation to the end user.

30 Figure 3.1 The five-layered adaptive hypermedia model based on LAOS framework [50]

LAOS clearly separates information- and presentation-goal to enhance information reuse, by separating chunks of information from a specific context. In this way, the approach simplifies the process of removing generality. This separation generates two major models – the DM and GM –, which allows a presentation to contain information relevant to a specific user, but which is drawn from multiple sources [44]. According to Cristea and Mooij [50], this separation provides high levels of flexibility. With the LAOS framework, it is possible to generate adaptive or flexible presentations, and the final presentation delivered to the user can include components of the domain model along with the components of the goal and constraints model. For example, the goal and constraints model can focus on clarifying a text attribute from the domain model’s parent concept, thus allowing the author to show different presentations from the single parent concept [50].

31 While the LAOS structure offers clear ways to implement an adaptation system, and whilst it is also a generic framework, it has been applied mainly in the area of education. The structure of the framework allows interaction between its layers. The number of layers could render it too complex for business owners. Moreover, a layer such as the Goal and Constraints Model in LAOS is not necessary in adaptive advertising, as it is supporting a story line, and a coherent delivery, which is more appropriate for educational applications than for advertising. Moreover, it has been designed to allow for the creation of standalone applications, without specific focus on portability and easy integration, which are the main goals of the research presented in this thesis.

3.4.3.SLAOS

The SLAOS framework [67] is an extension of the LAOS framework. It adds a new layer, the social layer, which affects all five layers of the LAOS framework, as illustrated in Figure 3.2. SLAOS integrates users with their collaborative activities. Similar to the LAOS framework, this approach supports standalone applications. In addition, as illustrated above for LAOS framework, it also contains a Goal and Constraints Layer, just as LAOS, which is not directly relevant to adaptive advertising. However, unlike the LAOS model, this model introduces the great step forward towards using social data. It adds a social layer that can interact with the previous five layers of the LAOS framework. A social component is also used in the model proposed in this thesis. However, in this research, the social component is added only to the user model.

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