Abstract
An intelligent tutoring system is a computer-based educational tool designed to provide adaptive learning environment to learners, mimicking the role of a human tutor. Its most typical areas of application are language learning, mathematics education, programming courses and medical training. Intelligent Tutoring Systems are based on the knowledge-module that is holding the system's knowledge in a well-structured format. Considering the current state of the art knowledge-module representations, a model that can represent evolving information is lacking. Representing evolving information is needed for those tutoring systems that are working with dynamically changing domains, e.g., software science. In this paper a new combined model is presented that is based on the ontology model and the fundamentals of knowledge space theory. The proposed model introduces the term of abstract time to be able to formulate an evolving knowledge graph. This paper introduces the term of evoking-hooks that makes it possible to realize connections between external domain elements and the nodes of the proposed model.
1 Introduction
In recent years the phenomenon of fast technological and societal change has reached an unprecedented level. Learning does not end by leaving the educational institutions especially for Information Technology (IT) professionals and programmers. It is expected that Intelligent Tutoring Systems (ITS) will increasingly appear in workplaces and everyday situations [1] due to the constant need for adoption to business change [2]. There is a high demand for self-regulated learning experiences as well as transparent personalized learning environments [3]. Due to this high demand several research activities were initiated to realize ITS systems. An ITS system is considered intelligent because it is mimicking the role of a human tutor by recognizing and monitoring the actual knowledge state of the learner and by able to change the learning path according to that. Knowledge representation has been conceptualized by numerous theories, for instance knowledge spaces, ontologies, rough sets, fuzzy sets, formal concept analysis, evidence theory, granular computing, etc., [4]. For an educational system a knowledge representation model not only has to support structural knowledge storing, but also needs to enable determination of actual knowledge states of the learner [5]. One of the most fundamental theories of knowledge state determination is Knowledge Space Theory (KST) [6]. Although several tutoring systems were developed over the years, only few of them utilized the advantages of KST [7]. While KST conceptualizes the knowledge as a set of questions or tasks, the Competence-based Knowledge Space Theory (CbKST) focuses on skills and competencies. Probably this is why most of the tutoring systems are rather using ontology-like knowledge representation where knowledge elements are more like real-life entities or terms and their elaborated description [8]. It can also be stated that the currently existing tutoring systems are focusing on domains that can be considered unvarying, e.g., math, chemistry, physics, etc., and has not been much effort in exploring evolving fields, e.g., computer programming.
In this paper a novel knowledge representation model is presented that unifies the advantages of CbKST and ontologies. Also, this paper introduces the term of abstract-time to the model to be able to represent time-dependent, evolving knowledge. The proposed model is a knowledge-graph that also allows building connections between existing knowledge forms, like textual documents or programming source code and the graph nodes that are called knowledge-units.
2 Related work
2.1 Educational knowledge representation with ontologies
According to Gruber [9] ontology is an explicit specification of a conceptualization. Ontology and/or semantic web based educational systems are grounded on the principle of entities and their hierarchical relations. In the most common scenario, an entity represents a unit of study; the relation between the entities represents the hierarchical relation between the units of study. Moreover, ontology is good for representing teaching strategies, student profile, modeling competence and learning goals, etc., [10]. Using ontologies, it is also possible to simplify administration processes [11]. The process of building an educational ontology relies on domain experts who are extracting domain ontology from existing learning materials [12].
Domain concepts can be well modeled by ontologies. Studying the ontology based tutoring systems two conclusions can be drawn. First, the knowledge domain that is represented by the ontology is usually separated from the educational content. Second, the ontological structure is grounded on natural object hierarchy, where the relation between the elements is based on generalization/specialization of the concepts represented by the elements [10]. In other words, the relation between the elements is not representing prerequisite relations, which is a key factor in epistemology. According to another observation, there are no two learning ontologies, designed by different people, would be the same [8].
2.2 Competency based knowledge space theory
According to KST the knowledge domain is represented by a network of nodes, where the nodes are questions or problems, and the edges are surmise relations [5, 13]. Based on the assessment theory some knowledge elements normally precede, in time, other knowledge elements. In other words, a certain question can be answered, or a problem can be solved only if some other questions have already been answered or some other problems have already been solved [14].
One important extension of KST is CbKST. CbKST is grounded on the observation that the learner needs skills to solve specific problems. Using the CbKST representation, the prerequisite relation can be determined by identifying the skills needed to solve the problems or to answer the questions [15]. In KST the set of questions that are needed to be answered to master a specific field of knowledge is called knowledge space. The learner's knowledge state is a subset of knowledge space, meaning those questions that the learner can answer. If the actual knowledge state of a learner is known, it can be defined where the learner can proceed (outer fringe) and it can be specified where to step back in case there is an understanding problem (inner fringe) [5, 14]. The knowledge state problem was also generalized further to assess the state of any system [16].
It may happen that the learner fails to solve a task that is lower in the hierarchy but can solve another task that is at a higher level. This is the consequence of a certain degree of instability of knowledge [17]. According to the original theory the learner's answer to a question is dichotomously classified as correct or incorrect. This is well suited for the classical domains, but in other cases, like: psychological assessment, attitudes, and opinions the dichotomous case appears to be too restrictive. To solve this problem a polytomous generalization of the model was presented [18]. In one of the latest extensions of CbKST the Competence-based Concept-Cognitive Learning Model (CbCCLM) was introduced where CbCCLM can study the transformation relationship between skills and knowledge from the perspective of competences [19].
2.3 Time dependency
In a well-known and general sense, time is a temporal concept that represents one specific moment or duration. One moment can be also called one time-instance and a duration can be called a time-interval. The Web Ontology Language (OWL) is a language for defining Web ontologies. The temporal properties of a real-world object can be represented by the OWL-Time ontology [20].
3 The proposed evolving knowledge space graph
3.1 General description of the proposed model
In this paper the Evolving Knowledge Space Graph (EKSG) model is proposed. The network that represents prerequisite relations in CbKST can be displayed in a precedence diagram. The units of study in ontology can be the replacement of question/problem nodes of this precedence diagram. Thus, using prerequisite relations and units of study, a directed graph can be constructed. The resulted graph combines the benefits of ontologies and CbKST. Additionally; two important features are added to the proposed model. To cover the requirements of an evolving domain model, time dependency is introduced, and the term of abstract time is defined. Although the term of time dependent graph is well known and studied [21] it has not been incorporated in educational knowledge representations yet. Second feature is the use of evoking-hooks that evokes certain knowledge elements by external triggers.
3.2 Abstract time
As opposed to the well-known and general meaning of time, in this paper time is considered as a higher-level abstraction. The reason why the model needs an abstract time property is to be able to represent evolving knowledge. There are domains where knowledge is not changing that fast, like mathematics, physics, or chemistry, etc. But in other fields, like the computer programming domain knowledge is constantly evolving.
From the perspective of change the term “time” does not have to mean Gregorian date-and-time. Software scientists invented the concept of “version” to represent change. A version behaves like a time instance. The main properties and functions of time concept, like “before”, “after” and “interval” are also interpretable in the concept of version.
Definition 1
The proposed general abstract time in the given domain is an ordered finite set of instance values that are strongly related to the domain. Formally:
Definition 2
Let
Definition 3
Let
Time delay is not interpreted in the proposed model.
3.3 Evoking-hooks
An evoking-hook is a word or set of words that can be found in a domain document and is strongly related to a node of the knowledge graph. For example, in the python-programming-domain the keywords ‘for’ and ‘in’ are evoking the ForLoop knowledge-unit. A similar solution is mentioned in the definition of FrameNet, where frame-evoking words are used to evoke elements of FrameNet [22].
3.4 Formal description of the proposed EKSG model
Definition 4
The proposed EKSG model is a labeled acyclic directed graph that can be described in the following way:
Remark 1
If the given time interval is empty the default value steps in, which is
Definition 5
There are several ways to process an evolving, time dependent graph. Here the so-called snapshot solution is described using discrete time-dependent units and time independent relations. Given the snapshot
Consequently, the described EKSG model can be considered as a sequence of static knowledge graphs
4 Experiments and analysis
The knowledge that is needed to complete the remove prefix or suffix operation is different in version 3.8 and 3.9. The structural difference can be seen in Fig. 3c.
According to the domain expert before version 3.9 the following prerequisites existed for the resulted PrefixSuffixHandling knowledge unit: NumberOfItems, Condition, StringDataType. Since version 3.9, the RemovePrefixSuffixFunction has only one prerequisite relation: StringDataType.
In the implemented data model with a simple cypher query the required knowledge structure can be requested, Code 1 is showing the query.
Code 1
Cypher query of determining the knowledge structure in version 3.8 for prefix and suffix handling.
5 Conclusion
Expectedly, in the next decade ITS systems will be part of everyday life. In these systems it will be increasingly important to represent evolving knowledge while maintaining the possibilities of personalized teaching. The presented EKSG model provides enough flexibility to represent a regularly developing knowledge domain.
The presented EKSG model unites the advantages of CbKST and ontologies by realizing a knowledge graph that utilizes the prerequisite relation concept from CbKST and real-life entities (knowledge-units) from ontologies. With introducing the abstract time concept to the system, EKSG is able to model fast evolving knowledge, e.g., computer programming languages. Adding evoking-hooks to the system EKSG can realize connections between knowledge-units and existing external knowledge forms, e.g., pieces of program source code.
The knowledge-units within the EKSG model must be atomic to build correct prerequisite relations, which is crucial to define personalized learning paths. This study will be continued with the aim of defining knowledge-unit atomicity as well as how learning paths can be efficiently predicted using assessment results and pedagogical techniques.
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