A Mechanism for Accessing and Mashing-up Pedagogical Web Services in Cloud

Learning Environments

Shueh-Cheng Hu

Dept. of Computer Sci. & Communication Engineering Providence University

Taichung, Taiwan, ROC schu@pu.edu.tw

Abstract-The current approach of packing and delivering instructional materials in asynchronous Web-based learning environments has a number of intrinsic drawbacks. To resolve them, it is rational to provide instructional data and activities in the form of services. To conduct service-composed instructional processes in cloud learning environments, a mechanism for accessing and mashing-up various pedagogical Web services is critical. This article aims to clarify the corresponding requirements and design principles, then propose a reference architecture for this mechanism accordingly.

Keywords-e-learning; cloud learning; Web services; REST: S�P

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I. INTRODUCTION

Today, most of Web-based learning management systems (LMS), including those standardized, i.e., the SCORM-conformant [1] systems, organize and deliver instructional materials with a monolithic approach. With this appr�ach, learners receive instructional contents through a learnmg management system, which is responsible for unpacking the pre-aggregated learning packages, enforcing pr�defmed sequencing and navigation rules, and delivering swtable contents to learners. Taking this monolithic approach looks an intuitive way to improve the reusability of costly-produced instructional objects, but it brought or eventually will bring multi-facet drawbacks to learners LMS administrators, and copyright owners [2].

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To resolve the problems of the monolithic approach, the concept of "cloud learning" or "service-oriented learning" was proposed by a number of researchers [3-5]. With the new approach, an instructional process could be composed by orchestrating a number of learning resources, which are offered in the form of services and serve different pedagogical purposes. The physical learning materials will not be fetched through service providers until learners request them during the course of instruction.

To achieve effective learning, the most valuable attribute of the new approach is able to dynamically seek a wide variety of pedagogical resources on the Web and then apply the most appropriate one to meet learners' occasional requirements, instead of being confined to use the materials that were pre-bundled in a package. This definitely will

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I -Ching Chen

Dept. of Information Management ChungChou Institute of Technology

Changhua, Taiwan, ROC jine@dragon.ccut.edu.tw

enrich learning experiences of learners with diverse backgrounds and objectives.

The other advantages brought by the cloud learning approach include the following: first, the better recentness and consistency of instructional materials will be achieved since the dynamic binding of instructional resources ensures that learners can fetch the latest updated instructional contents from providers on demand. Second, from the perspective of contents producers or copyright owners the service-oriented approach of delivering instructional contents enables the centralized scheme of controlling their valuable digital resources. Consequently, a centralized-paradigm could be established to conduct access control, rights management, and maintenance works more efficiently and effectively, comparing to the monolithic approach. Third, because of popularity and easy access of its enabling technologies including HTTP, XML, and SOAP, an environment that support cloud learning represents an open and easy-to-share platform, which is not only ben�ficial to learners, but also convenient to those who try to deSIgn, produce, market or just contribute their creative digital works for educational purposes. This is critical since many successful Web 2.0 applications' experience indicate that the foundation and flourish of a knowledge community need active producers as well as consumers.

Despite some ideas have been proposed to conduct the cloud learning or similar concepts, rare work [6] has been done to architect and implement working environments or even prototypes for realizing a generic cloud learning platform. However, the Instructional Management Systems Global Learning Consortium (IMS), an organization that de�nes and maintains relevant standards for e-learning, has noticed the trend of service-oriented provision of instructional materials, and is taking proactive steps to define associated standards: common cartridge (CC) and leru:ning tool interoperability (L TI) [7], which aim to keep vanous external pedagogical services can interoperate with different LMSs in the future.

To realize the concept of cloud learning, the environment supporting service-oriented instructional processes must equip a mechanism that can access various pedagogical Web se�ic�s and mashu� available services according to learning obJectIves, learners profile, and other factors. This article aims to clarify the requirements and design principles of

such a mechanism. In addition, the reference architecture and key implementation issues also are presented.

The remaining parts of this paper are organized as follow: section II briefs the two types of Web services. Section III discusses the access and mash-up issues of pedagogical services. SectionN presents the design rationales and the implementation issues of a reference architecture. Concluding remarks are outlined in the last section.

II. PEDAGOGICAL WEB SERVICES

In this section, the enabling techniques of a cloud learning platform will be briefly presented first. Then, how different pedagogical services could be offered with appropriate Web service techniques will be discussed.

The cloud learning or service-oriented learning approach fundamentally change the way of provisioning the learning materials. Basically, pedagogical resources are prepared and accessible through Web service providers during instructional process, as figure I illustrates. In other words, all pedagogical resources on the Web could be wrapped and offered in the form of service, and then, learning management systems can request required services on behalf of learners.

Cloud holding pedanonical resources -----------

Learning plalfonn supporting cloud learning approach

figure I The provision of learning materials in cloud learning environments

Although their applications in e-Iearning domain is not pervasive, Web service technologies have been widely adopted in e-business [8] and e-commerce [9] areas since late 1990s. Web service technologies enable the service-oriented architecture (SOA) [10, 11], a new paradigm for software system design and implementation. Due to the platform-neutrality of its two fundamental elements: XML and HTTP, Web service is able to integrate distributed, heterogeneous information systems to fulfill a new requirement. This might explains why it has been widely adopted in many applications of enterprises that always must come up with solutions for facing new challenges, but need to take into account their long-haul investment on information systems simultaneously.

When Web service techniques were applied in the provision of e-Iearning materials, its platform-neutrality characteristic means no matter which implementation techniques and operating platforms were chose, once an

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instructional resource was developed or just wrapped as a service, all clients on the Internet can send compliant request to access it. Obviously, that will leverage the reusability and sharing of learning objects and instructional processes beyond the current level.

Basically, there are two kinds of Web service enabling technologies: SOAP (Simple Object Access Protocol) based and REST (REpresentational State Transfer) styled. In early stage of its development, the Web services include three core technologies: SOAP, WSDL (Web Service Description Language), and UDm (Universal Description, Discovery and Integration) [12], thus, the services using these techniques are called SOAP-based. The SOAP-based Web service requesters and providers need to handle XML-encoded SOAP envelopes whenever a request or a response was sent and received; i.e., a significant amount of computing overhead is required to conduct the SOAP-based communication protocol. As a result, the SOAP-based Web services became bulky to sites with intensive traffic. To respond to the issue, Roy Fielding presented the REST-styled services in his dissertation [13].

On the contrary, due to its comparative simplicity in protocol, computation process, and usage, the REST-styled Web services has being quickly embraced by many Web-based enterprises including those leaders such as Google, Yahoo, Amazon, eBay, Facebook, etc. Although the REST-styled Web service has been gaining popularity at the cost of SOAP-based services, the later one still have a number of advantages such as stronger typing, supporting transactions, and stricter service contracts. Thus, SOAP-based techniques can realize more complex distributed applications.

To exalt the merits of each Web service technique, pedagogical resources could be classified into two categories: instructional data and instructional activities. Accordingly, corresponding services can be designed as data providers and activity facilitators, respectively. For those services that aim to offer learners instructional data such as practices, assessment items, supplementary materials, a synchronous and stateless connections between the intermediary LMSs and service providers will be sufficient to fulfill its function. Consequently, the lightweight REST-styled Web services can properly serve as instructional data providers.

On the other hand, during the course of instructional processes, many activities such as formative assessment and online discussion forum, need repetitive interactions among participants who might be learners, instructors, tutors, or imitated intelligent agents. Usually, the states of communication need to be preserved for progress-tracking and other pedagogical purposes. Besides, asynchronous communication is necessary to support those long-lived and human-involved instructional activities. Based on these requirements and the stateless principle of REST services, SOAP-based Web services emerge as a better option for conducting instructional activity facilitators.

III. ACCESS AND MASHUP OF PEDAGOGICAL SERVICES

In a cloud learning environment, pedagogical services need to be pre-linked or dynamically bound during an

instructional process. The service access module must be able to seek available services that are appropriate to a leamer's profile and learning objectives. After identifying the required service, the access module needs to send compliant service requests to target service provider. To access both SOAP-based and REST-styled services, the corresponding service specification techniques; WSDL for SOAP and W ADL (Web Application Description Language) for REST, need to be implemented in the service access module.

In the service-seeking phase, the access module needs to query the repositories where SOAP and/or REST services had been registered, then to send requests to providers that can fulfill required instructional functionality. To find out appropriate services, it is necessary to match instructional requirements with the pedagogical attributes of available services. The standard for describing learning objects: the IEEE LOM (learning object metadata) [14], has been included in many relevant specifications, can be used to describe the pedagogical attributes of SOAP and REST services.

Besides obtaining the access of data or activities through service providers, there must be a mash-up module for orchestrating a series of available services to complete an instructional process. Usually, instructional designers or instructors need to design an instructional process according to learning objectives and learners' profile in advance. Obviously, the mash-up module must be able to specify various instructional processes by using the constructs of a service-enabled process description language such as the WS-BPEL [15].

The invention of WS-BPEL carne from that the process-oriented approach to SOA requires a language for describing how a number of Web services should be composed into a business processes. The major function of WS-BPEL is allowing process designers to define abstract and executable processes, which are formed by chaining a various activities including invocation of Web services. The expressive capability of the five structured tasks (including sequence, switch, pick, while, and flow) in the popular WS-BPEL is sufficient to program the similar sequencing and navigation rules that are widely adopted in the current LMSs.

IV. DESIGN PRINCIPLES AND THE REFERENCE

ARCHITECTURE

In this section, two design principles of a mechanism for accessing and mashing-up pedagogical services in cloud learning environments will be settled first. According to the requirements discussed in the previous section and the design principles, a reference architecture of such a mechanism and corresponding implementation options were proposed.

To make current Web-based LMSs still function as usual, the service access and mash-up mechanism needs to be designed as an expansion, instead of an integrated part of a current LMS, which is an application deployed within an application server.

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To keep track of and persist learners' status and progress, all service request and response messages must go through the central control unit in a Web-based learning environment: LMS. Thus, the LMS will send a learning requirement to the service access proxy, which then search and bind an appropriate provider. All response messages from providers will be sent to the LMS first, and will be forwarded to the client after necessary book-keeping works. In other words, even it has this kind of capability; the client will not contact the service providers directly.

Web application server

Learning management system (Moodie)

figure 2 A reference architecture of the access and mash-up mechanism in cloud learning environments

Based on the prior requirements and design principles, the reference architecture of the mechanism could be depicted as Figure 2 shows. There are three major modules in the service access and mash-up mechanism: mash-up module, proxy module, and service registry module. The mash-up module contains a Web application in which service-oriented instructional processes could be described and executed. The open-sourced ActiveBPEL [16] will be a proper option for fitting this role. The service registry module can utilize the Adjoovo Spaces registry [17] due to its support for registering and locating both REST and SOAP services. The proxy module is a WSDL- and W ADL-awared service broker from which all requests will be sent to service providers.

V. CONCLUSIONS

The concept of cloud learning resolves a number of problems those are inevitable in the current Web-based learning environments. Not only resolving the drawbacks, the service-oriented approach of provisioning instructional materials can facilitate the reusing and sharing of pedagogical resources on the Web.

Nevertheless, the realization of this concept needs to take practical factors into account, such as the compatibility with existing e-Iearning environments, the efficient access of required learning resources that are in the form of services, and the interoperability between different modules in the mechanism and other external services in cloud learning environments.

This paper aims to analyze the fundamental requirements and settle a set of design principles for the service access and mash-up mechanism in a cloud learning environment and propose a reference architecture accordingly. The prototype for proving the concept could be built by utilizing a number of open-sourced software packages.

Among many foreseeable challenges, how to achieve the compliance to standards insuring the interoperability between external pedagogical services and LMSs is the most significant one since the key standard: the IMS learning tool interoperability is still under development at this moment. However, the loosely-coupled approach of service-oriented architecture can reduce the revamping works for adapting to the fmalized standards.

REFERENCE

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[15] OASIS, "Web Service - Business Process Execution Language (WS-BPEL)," http://www.oasis-open.org/committees/tc_home.php?wg_abbrev=ws bpel,2006.

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