Java Learning Object Ontology

Transcription

1 Java Learning Object Ontology Ming-Che Lee, Ding Yen Ye & Tzone I Wang Laboratory of Intelligent Network Applications Department of Engineering Science National Chung Kung University Taiwan limingche@hotmail.com, aska@lina.es.ncku.edu.tw, wti535@mail.ncku.edu.tw Abstract This paper presents an ontology, the Java Learning Object Ontology - JLOO, for organizing learning objects of Java courses in an adaptive e-learning environment. The classification is based on the Computing Curricula CC2001 of the ACM and IEEE/CS. Using the curriculum as a guideline, the ontology defines the atomic knowledge units (i.e. learning objects) for an introductory course of Java programming. The most significant contributions of JLOO are: 1) defining the atomic knowledge units of introductory courses of Java language, and the relationships among them, 2) making the knowledge units of JLOO sharable and reusable, 3) allowing different learning strategies of a e-learning environment to choose dynamically, using JLOO as a guideline, different learning paths, and 4) making the realization of adaptive learning easy. 1. Introduction In 2001, The Joint IEEE Computer Society/ACM Task Force on the "Model Curricula for Computing" (CC) published the Computing Curricula 2001 (i.e. CC2001) [1] that contains curriculum recommendations for undergraduate programming courses in computer science. The report also called for additional discipline-specific volumes for each of computer engineering, information systems, and software engineering. In the curriculum six top-level concepts are suggested for the programming fundamentals; they are Data model, Control structures, Order of execution, Encapsulation, Relationships among encapsulated components, and Testing and debugging respectively. To introduce object-oriented programming, Java is the most common used language because of its popularity and practicability. Different educational strategies may lead to different learning paths in Java course. For example, if an institute chooses Object-First as their teaching strategy, Class and Object concepts may be presented first in its course. However, if Functional-first is chosen, some functional programming languages and algorithms may be presented before Java, and Java course can start from syntax, procedure rules, or data structures instead of class and object. This paper presents a Java Learning Object Ontology JLOO, which is used as a guideline in developing the learning objects of introductory Java courses and in organizing these learning objects in an adaptive learning environment. The work is based on the Computing Curricula CC2001 of the ACM and IEEE/CS. JLOO focuses on the basic knowledge units in Java language without considering other advanced Java programming features (such as swing package, network programming, or multi-threading). The rest of this paper is organized as follows: section 2 describes the concept of ontology in brief, and analysis the methodology for building ontology. Section 3 describes the structures of JLOO in detail. Section 4 is a case study in class tutoring. Different strategies and learning path are also examined in this section. Conclusion and future work are given in section Ontology concepts and methodology Ontology is a philosophical theory about the nature of existence. Artificial Intelligence researchers reincarnate this term as their own jargon for expressing a shared and common understanding of some domain that can be communicated between people and

2 application systems [2]. A typical ontology has a taxonomy defining the classes and their relationships and a set of inference rules powering reasoning functions [3]. 2.1 Ontology Definitions Ontology is recognized as a term referring to the shared understanding of some domains of interest, which is often conceived as a set of classes (concepts), relations, functions, axioms and instances [4]. Guarino [5] established a comprehensive survey of the ontology definition from the high cited relevant works in the knowledge sharing community. For the purpose of this paper, an ontology is a formal description of concepts in a domain of concepts (we use class in this paper), properties of each concepts describing various features and attributes of the concept ( slot is used in this paper), and restrictions on slot ( facets is used in this paper). 2.2 Methodologies for ontology development This sub-section describes our methodology for JLOO development, which is called purpose-oriented model. Here we discuss general issues to consider and offer one practical process for developing an ontology. The steps are: (1) Determine the domain and purpose of the target ontology. Defining explicit domain and purpose is the most important step in developing an ontology. For example in JLOO, the domain is targeted at atomic knowledge units of introductory Java language. So the class hierarchy is constructed by learning concepts, and Java APIs are not mentioned. (2) Consider reusing legacy ontologies There are libraries of reusable ontology on the Web and in the literature, such as Ontolingua ontology library [6], DAML ontology library [7]. Lots of commercial ontologies are also available (e.g. UNSPSC [8], RosettaNet [9], DMOZ [10]). If one considers to reuse existing ontologies, it s necessary going back to step1 and check the originally purpose. (3) Survey important terms in this domain It is useful to write down a list of all important terms (or terms that have special meaning). The scope must also be limited to the domain and purpose of this ontology. (4) Define classes and class hierarchy Hhow to build a class hierarchy (in other words, considering which terms should be classes) strongly depends on the expert s view and the purpose. We organize the classes into a hierarchical taxonomy by referring two principles: (a) Each instance of B is an instance of A, if and only if B is a sub-class of A (b) If C has no instance, then C should be considered as an instance. (5) Define slots of classes What slots should be added into a class also depends strongly on the purpose of the target ontology. For example in JLOO, String is a formal learning concept (i.e. a class). But in Java, Strings are objects. Specifically they are the instances of the class Java.lang.String. While the purpose of JLOO is to provide a learning object knowledge base, not a Java APIs inventory, the package path (Java.lang) has no reason to be a slot in the String. (6) Create instances The final step is to create the instances of the classes. If an instance is unconcerned with the purpose, it should not be created. This step also refers to the principles in step The structure of Java Learning Object Ontology This section describes the ontology developed in this paper, the JAVA Learning Object Ontology JLOO. 3.1 Definition of Learning Objects The term Learning Objects is defined based on the Declarative Knowledge Representation the knowledge of facts, concepts, principles, and mental model [11]. The normal descriptions of these four knowledge types in related to Java programming language are: Facts "Know what"; Fact is a statement that explains the relationship between two objects or events. For example in Java, all the Arithmetic operators (+ (unary plus), - (unary minus), *, /, %, +, -) are Facts.

3 Concepts Know that A Concepts is a class of items, words, or ideas that are known by a common name, shares some common features and includes multiple specific examples. In Java language, declaration statement could be a concepts. Principles Know why A principle is a type of relational rules that can be used as if-then or cause-effect relationships. For example, in Java, Double-selection structure (if/else), and Multiple-selection structure (switch) could be the principles. Mental Model A mental model is a network constructed from facts, concepts, and principles. For example, in Java, many higher level abstractions, such as the Recursion or the Iteration could be defined as mental models. fit as possible to the original description for the data model in CC2001, which is Standard structures for representing data; abstract (described by a model) and concrete (described by an implementation) descriptions. In addition to the primitive types in Java language, class, the user defined data type, are also included in JLOO. The Control Structure Concepts As mentioned above, Learning Object is defined as: a significant instruction entity (maybe a text, a talk, a test, or other kinds of representations), which belongs to a fact, concept, principle, or mental model. 3.2 Classes and class hierarchy This sub-section describes the classes and the class hierarchy of JLOO. Protégé 3.0 beta [12] is used to build JLOO. The leaf nodes are the concretizations of facts ; they are the template definitions of atomic learning objects which can have various learning contents for the facts. A non-leaf node, on the other hand, represents the concretization of concepts, principles, or mental model ; an instance of it should integrate, in some form, the instances created from all the leaf nodes that are direct descendants of the node. Figure 2. Sub-Class Hierarchy of Control structure The original description of control structure in CC2001 is: Effects of applying operations to program objects; what an operation does (described by a model); how an operation does it (described by an implementation). It implies the inclusion of all the expressions and statements in programming languages; thus, they are included exactly as expressions and statements concepts in JLOO and shown as that in figure 2. The Order of Execution Concepts The Data Models Concepts Figure 3. Sub-Class Hierarchy of Order of Execution Figure 1. Sub-Class Hierarchy of Data models Data models cover the basic data types in Java and some simple concepts in OO paradigm. They adhere as The original description of order of execution in CC2001 includes: Standard control structures: sequence, selection, iteration; function calls and parameter passing. This description implies that the execution order maybe different while some variables

4 values are changed. The results in JLOO are shown as in figure 3. The Encapsulation Concepts. Figure 6. Sub-Class Hierarchy of Testing and Debugging Figure 4. Sub-Class Hierarchy of Encapsulation The primary description of encapsulation concept in CC2001 is: Indivisible bundling of related entities; client view based on abstraction and information hiding; implementer view based on internal detail. This implies the necessity in the course to comprise OO concepts (client view) and the related syntax (implementer view). Thus, JLOO contains the necessary knowledge in the hierarchy. The result is shown as in figure 4. The Relationships among Encapsulated Components Concepts. Figure 5. Sub-Class Hierarchy of Relationships among Encapsulated Components The original description of the relationships among encapsulated components in CC2001 states: The role of interfaces in mediating information exchange; responsibilities of encapsulated components to their clients; the value of inheritance. The concepts are reflected in JLOO as composition, inheritance, package, polymorphism, and scope rules as shown in figure 5. The Testing and Debugging Concepts The description of testing and debugging concepts in CC2001 is just: The importance of testing; debugging strategies. In fact, the concepts of testing and debugging are hard to be classified. Referring to the debugging and testing techniques found in software engineering, JLOO classifies the concepts as error types, testing strategies, testing techniques, and etc, as shown in figure Definition of Slots In JLOO three specific slots are defined for a concept: PREREQUISITES MUST-TAKE OPTION-TAKE They are discussed as follows PREREQUISITES Part of the values of PREREQUISITES indicates the learning objects that must be learned first to gain the prerequisite knowledge before studying an instance learning object of this class; i.e. a learning object is not to be taught unless that the prerequisite condition is satisfied. The remaining values indicate some learning objects that can be optionally learned. Figure 8 illustrates the concept of PREPREQUISITES. To enhance the scalability and flexibility of PREREQUISITES, two template classes, AND-GATE and OR-GATE (both with type Boolean ) are added in JLOO. The meaning of AND-GATE and OR-GATE is similar to the logic gates. Figure 10 shows two examples. On the right side (Multi-selection Structure (switch), Class Method use Static) are the target learning objects, and on the left side are the corresponding prerequisite learning objects. That is, the AND-GATE points to the required objects. All the objects that connect to the left hand side of the AND-GATE must be taken, i.e., the AND-GATE will be set true if and only if all the connected objects were

5 done (in the reality, for example, pass a test). The OR-GATE will be set true if and only if one of the connected objects was done. Name constant Variable Initializtion Call Assignment public static Value-returning Method Void Method break Primitive Type Modifiers Method Multi-selection Structure (swtich) Class Method use Static Figure 7. Case Study of Type Class There are two significant implications of PREREQUISITES. (1) As the first case shown in figure 7, there are multiple ways to get into Multi-selection Structure (switch). Also at the second case, to get into Class Method use Static, there are multiple selections. Different learning strategies may choose different paths, especially in an e-learning environment. In such an environment, the course structure is quite different from the traditional instruction, such as the concept-oriented instruction, programming-skill-oriented instruction, or even the certification-oriented instruction that with limited teaching hours. In the implementation, we referred to experts opinion and gave each learning object the corresponding prerequisite values, which could be the minimal restriction of the learning path chosen. (2) With different learning paths, the content of the target learning object should be adjusted. For example, as the first case in figure 7, if the prerequisites of the target is Variable ; Assignment ; break; Primitive Type, the content of switch should not include Initialization or others MUST-TAKE & OPTION-TAKE. These two MUST-TAKE and OPTION-TAKE are used to describe the non-leaf nodes of the class hierarchy. As mentioned in a previous section, non-leaf node is the concrete knowledge with types concepts, principles, or mental model, and the learning content is constructed by its children. The value of MUST-TAKE records the must take learning objects, and OPTION-TAKE records the optional learning objects which can enhance the comprehension of the target. Ontology (JLOO), which is used to be a guide for various learning strategies chosen. As we showed above, JLOO is a reusable and sharable ontology. In most institutions, programming skills (at least programming fundamental concepts) are provided in the introductory courses, i.e., students may touch this domain at the first year of college. With the specific slots, JLOO is easy to help teachers to build the most suitable instruction process. This paper also presents a purpose-oriented methodology that we use to build JLOO. Comparing with the existed ontology development methodologies, the proposed methodology provides a more practical way to build a domain specific ontology. References [1] Computing Curricula of The Joint IEEE Computer Society/ACM Task Force. [2] Gruber, T. R., Toward principles for the design of ontologies used for knowledge sharing, IJHCS, 1994, no. 43(5/6), pp [3] Tim Berners-Lee, James Hendler, and Ora Lassila, The semantic web. Scientific American, 2001, May. [4] Gruber, T. R., A translation approach to portable ontology specifications, Knowledge Acquisition, no. 5, pp , [5] Guarino N., Understanding, Building and Using Ontologies: A Commentary to Using Explicit Ontologies in KBS Development", by van Heijst, Schreiber, and Wielinga, International Journal of Human and Computer Studies, no. 46(2/3), pp , [6] [7] [8] [9] [10] [11] Gagne, R., The conditions of learning, New York: Holt, Rhinehart and Winston, [12] 4. Conclusions This paper presents a Java Learning Object