CAN P2P DELIVER WHAT WEB REPOSITORIES PROMISED: GLOBAL SHARING OF E-LEARNING CONTENT? Reinhard Kronsteiner1, Edgar R. Weippl2, Ismail Khalil Ibrahim1, Gabriele Kotsis1 1)
Deptartment of Telecooperation, Johannes Kepler University Linz, Austria {reinhard;ismail;gk}@tk.uni-linz.ac.at 2) University of Vienna,
[email protected]
Abstract Since the emergence of e-learning several years ago, the anticipated benefits of sharing content using P2P networks have not really been achieved yet. Clearly, sharing of music and similar content works fine using P2P technology. In this paper we explore whether and how P2P network technology could be used to share e-learning content. Our contribution is to analyze the requirements for P2P content-sharing and to elaborate on the prerequisites for building more successful attempts for sharing e-learning content. The result of our work will help others to create successful P2P e-learning networks.
1.
Introduction
P2P computing has emerged as a network model that is expected to be the basis for many applications in the near future. P2P computing can be viewed as infrastructure for supporting the creation of information sources, facilitating the process of dynamically and directly exchanging of information and services across global networks, and allowing the effective and efficient interaction among content producers and consumers in real time. This has been fueled by the explosion of unstructured data, the need to formally mange content, and internetworking and collaboration within and between enterprises which made P2P network model the most appropriate model for distributed content management systems. P2P provides access to content wherever it resides regardless of data structure and the information's native format. It provides an unprecedented number of ways to obtain information, acquire services, and vastly improve collaboration. One can create content while maintaining some control over it, and collaborate efficiently by sharing data in real time with a distributed network of users. Two approaches have been advocated for the design and implementation of P2P content networking; in the informal approach, the access to index and directory services and their related resources is uncontrolled by formal corporate polices. Examples of this approach is Napster [18] and Gnutella [3] while in the formal approach, a strictly controlled access to index and directory services residing in both the server and the client, and related sources is defined and monitored through protocols at the network level, examples of this approach are NextPage [17] and Groove[4]. These two approaches can be compared qualitatively and quantitatively with respect to security, policies and workflow.
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The formal approach can be used in situations where access to distributed, business-critical content is needed without attempting to centralize the date while the informal approach can be used in situation where the content management solutions is highly dependent on sharing real-time information across geographically disparately distributed resources. Due to the nature and characteristics of e-learning systems, P2P technology seems to be the most well suited mechanism to deal with the problems and challenges associated with e-learning. These include the massive amount of data that is stored and maintained by multiple information sources, the heterogeneity of the data objects, the dynamicity of e-learning components and the multimedia nature of the underlying data. Current e-learning systems can be arranged according to their potential of control. We differentiate between strict controlled and loose controlled learning systems. Strict controlled systems define a clear process for the participants to wade through the learning material. Loose controlled learningsystems allow participants the highest possible degree of freedom in constructing their learning processes. The p2p e-learning application we propose in the sequel of this paper aims at loosely controlled systems. P2P offers great opportunities for the delivery of e-learning content, but it needs to be controlled and integrated into the rest of the e-learning system. While traditional Computer-based training (CBT), Web based training (WBT), web lectures, ebooks, Electronic Performance Support Systems (EPSS) are fine for information transfer, they don’t provide the model and capacity to allow the learner to take control and practise over the learning cycle which can be offered through P2P networks. In this paper, we explore whether and how P2P network technology could be used to share elearning content. The paper is structured as follows: in section 2 we present an e-learning scenario to show the need of adopting P2P technology, sections 3 and 4 substantiate our approach of architecture, this paper finalises with a critical evaluation of our work and the references to related work.
2.
E-learning scenario
In order to highlight the strength and drawbacks of a P2P content delivery network in the context of e-learning, we show that P2p is an efficient way of distributing large volume data. While offering unparalleled freedom the unstructured layout however, does not sufficiently support required services such as DRM. Thus, we propose to combine the powerful distribution mechanisms with server-based mechanisms. Computer Supported Collaborative Learning (CSCL) – a term that has been established a decade ago [5], [6],[14] – is learning based on interaction among learners and instructors. The learning is online and communication can be supported in one of two ways, either asynchronously, or synchronously. Asynchronous communication include discussion threads, e-mail and shared room databases. [5] These techniques allow learners to share access to a common set of materials, such as files, software, and media objects, and to collaborate on assignments and projects irrespective of time and place. Typically, asynchronous collaboration is instructor-facilitated. That is, the instructor is not available in real-time to support the learners, but interacts with the learners offline through the same e-mail and shared databases. Project evaluation, assignment allocation and quizzes can all be handled in this way.
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Real time or synchronous collaboration provides real-time, simultaneous access to content, instructors and other students. Synchronous collaboration is typically instructor-led. That is, the learners access the instructor in a virtual classroom environment. The instructor guides the learners through interactive online learning, such as shared whiteboards, shared application software, electronic hand-raising, chat functionality and audio/video over the network. Both scenarios consist of two main components, an e- learning material and its digital presentation which we call e-learning content henceforth, and the communication process which we call interaction protocol.
3.
P2P e-learning System Architecture
In this work, we solely focus on the specification of communicational infrastructures for P2P in the context of e-learning content sharing and messages exchange. As a first step, we identify the core functions (notions) on which our proposed architecture is to be founded: 3.1. Roles and Users: In any P2P, users are the main players. Roles are the standardized pattern of behaviour of users. The identification and regulation of roles is considered as part of the formalization process of the elearning system. For e-learning scenario, we can identify the following roles: •
Community of Interest: Group of people who share the same interest on a specific topic or want to learn the same thing. Community members are either students or tutors but can also adopt the role of content provider if needed. Each member of a community can be in more than one group (organized by peer-profiling as mentioned in [21]). Communication between communities is out of the scope of this paper.
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Content-providers: People or organizations that are responsible for the static content, the base material of knowledge for the community of interest.
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Tutors: People who support the community of interest in achieving their goal to increase knowledge through cooperation by reviewing of material and providing further information about this material.
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Learners: Learners are the consumer of information. They try to increase their knowledge, based on the material given by the content-provider and through communication with other learners or tutors.
There are several issues concerning role/role relationships. As a user may possibly play several roles at the same time, role/role associations standing for conflict of interests must be defined with the goal of protecting the e-learning system from user’s malicious behavior. Thus, in general, the management of user/role and role/role relationships becomes a fundamental issue for P2P e-learning system. Role-based Access Control Models (RBAC) [19] developed in the computer security arena offer well founded mechanisms for handling both types of relationships. Although RBAC manages three types of associations, namely associations between users and roles, and associations between roles, and associations between roles and permissions, in this paper we solely concentrate on the role/role associations. Another important issue when analyzing e-learning systems, we observe that roles are hierarchically organized. There are many ways of constructing of a role hierarchy to express different types of relationships among roles. As an example the content provider is responsible for his content, but the content also can be enriched by the tutor which is furthermore consumed by the student. The hierarchical order also shows the level of trust in the system. Students trust the content provider. The content provider trusts the tutor but not students to change his documents, etc. 220
3.2. Architectural Components: Today’s P2P networks differentiate between peers and advanced peers (Relay Peer in JXTA) [10]. Relay Peers just have the benefit that they know which peers are available at the moment in the network. They distribute the messages between other peers and are needed to establish ad-hoc connections. •
Peer: Each peer assigns a shared directory for access by other users. Upon connection, each peer registers at the Relay Peer with its index and its search requests. The search request can be handled either online or the central index can inform the peer about results on its search.
•
Relay Peer: The relay peer manages the communication between other peers and peer groups. Each group is dedicated to at least one relay server but only one relay server can manage various groups. The relay peer gets the search requests for each peer and informs them when and where something is available and who is available in the actual situation.
3.3. Content Document Structure: A content document plays a central role in our scenario. A content document has an owner and a meta-text which informs about its topics. This meta-information will be indexed at the owners peer and delivered with the content document whenever this document is requested. We call the content document static content. •
Versioning of static content documents: Each document needs a version to be identified over the network. If the owner of the document updates this document, all users need to be informed to download the newer version of the document. This can be done via messages. It also should be possible to delete files remotely if they are not changed by the local user.
•
Comment-document: All participants can make their comments to a document. These comments will be distributed within the document or separately. A comment (we call it dynamic content) can be a practical example, additional information, review information, etc. A comment document is also a document and needs to be updated. The receiver of documents can decide whether they want to download the comments or not.
•
Access / download restrictions: Digital Right Management (DRM) is one of the main features in our e-learning system. First the owner of a document needs to be identified, second the root of each comment needs to be documented. DRM is not just necessary to defend copyright interests. It can also be used to certificate the root of information and its trust-worthiness. The community of interest should decide which//whose documents they receive. Do they receive all documents or comments to the already saved documents, or do they just receive documents and comments from groups or specific persons they trust. Also the owner of a document should decide for whom the information is planed to be given. Is the information is for whole groups or just for specific persons.
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Document-Relations: The document relations associate the content stored on the peer’s shard directory. The sum of document relations builds a knowledge map for each peer which is accessed by the relay server. This central index carries all actual documents online and can be searched by users. If the user logs on to the system she sends her own personal index to the server so that the server can provide sources for the different information.
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Peer
RelayPeer Request
Content..n
Connection Information
File
Doc ument
Query
Content..i Metainformation
Peer-Kowledge-Map Versioning information Annotation Access restric tions Documtent relations
Figure 1: Content Document Structure
3.4. Message Exchange: Messages in this model are responsible for the workflow. All messages are sent via the Relay Peer that distributes the messages and stores messages that are sent to the group of users. This is necessary to provide update functionality and helps to enable a kind of workflow in the system. Messages from one online user to other online users are sent directly 3.5. P2P e-learning Processes: •
Document sharing
•
Comments on documents
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Document changing
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Message exchange
We want to introduce the review process for documents and messages to our scenario although they are usually found in class-room scenario. The role of content provider is taken by the person who introduces the content to the community. The student consumes the information and can change his role to a content provider as well. Relay Peer
Notification Message Exc hange
Document Update
Document Sharing
Peer
Peer
Learner Connec tion Information
Annotations on Documents
Tutor
Peer
ContentProvider
Community of Interests
Figure 2: System architecture
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The relay peer handles the connections between the peers and the message exchange. This message exchange is necessary for all kinds of notification about new documents, changes and added annotations.
4.
Sharing Content
In this section we first highlight the strengths and drawbacks of P2P in the context of e-learning. We will then continue to show which criteria are essential to success. Our results are based on analyzing existing P2P technology, including both research prototypes such as LOMster [20] and also commercially successful ones including Kazaa [11]. •
Advantages and Disadvantages of P2P e-learning
There are several advantages of P2P compared to other ways of sharing content. First and foremost it is easy to use. Everybody who has used Morpheus or Kazaa knows that both downloading and even more important - sharing is very easy.
+
–
Easy-of-use
Security
Encourages sharing
Critical volume required
Rating systems of content
Rating systems not powerful enough
Second, since downloaded content is placed per default into the shared folder, sharing is encouraged. Moreover, Kazaa, for instance, assigns a participation level to each user indicating whether he or she shares a lot or not. More specific this participation level represents the ratio of uploads and downloads. Users with a higher participation level get priority over others. Therefore, this also serves as an incentive to share. Modern P2P clients offer a way of rating the content. Kazaa, for instance, allows users to rate the integrity or quality (on the levels poor, average, excellent). The rating is essential to ensure that high quality content spreads faster than low quality and just can be done by a qualified instance of trust. Rating systems are still very limited. For popular (illegal) content such as MP3 the title and a rough quality rating may suffice. In the context of e-learning more detailed meta-data would probably be useful. Quality of contributions and the quality of metadata are clearly essential to the success of any P2P approach. Even if rating schemes do not work reliably in existing networks we are confident that given a DRM this can be dramatically improved. Only few people give accurate ratings of quality and usually do not complete metadata for MP3s. The main reason is the missing incentive to do so. Users have to act anonymously and often change pseudonyms to avoid being tracked when illegally sharing content. We can use p2p networks in the sub process of fact-finding. Peers can grant access primary to their content but also to the roots of their content (i.e. primary information). This access to a pool of primary content leads us to more complete view on produced content and therefore knowledge. Despite all the advantages P2P generally suffers from various drawbacks. Security is the first major concern when sharing content. In Kazaa mainly MP3 and the other digital content is shared. These
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files cannot contain malicious payload such as viruses. However, when sharing executables or office documents the risk of infection is high. E-Learning content typically includes also these file types. However, in a scholarly setting, people would in many cases not want to remain anonymous. First, there actions are not illegal and second, “being known” and respected by many others is one of the major drivers in scholarly activities. Given a reliable DRM, content would be signed and thus the identity of the contributor is known. Third, the last major drawback that P2P approaches may suffer from is that not enough content is available within the network. This is mainly caused by the aforementioned lack of quality. Given even a reasonable number of high quality content, users will be drawn to the P2P approach and over time the content base will most certainly grow. 4.1. Requirements Drawing from the experience with existing P2P networks and a study of several experimental networks (LOMster [16], Edutella [15]) we will now look at the prerequisites for a P2P network to share e-learning content. Based on our findings it will be easier, though definitely not straight forward, to build such a P2P network In this paper, we adopt as a main goal the availability and search ability of content. Similar to Lionshare [12] we propose to use an existing P2P standard (such as Gnutella's communication protocol). In addition we incorporate a DRM component to control access to content. The Internet has leveraged the opportunities for students to act dishonestly according to academic standard. Plagiarism, although not a new phenomenon, has received increased attention due to the fact that sharing term papers over the Internet has become common misconduct. P2P is associated with boundless and uncontrolled sharing. However, given a simple DRM component, access to content can be traced in case of suspected plagiarism auditing records can be analyzed. Figure 3 illustrates a way of encapsulating digital content into cryptographic containers. The mode of distribution is irrelevant for the authentication, access control and auditing mechanisms. Authentica tion Server (AS) 1. User sends authentication data
2. Server sends signed ticket enc rypted for TGS back to the c lient viewer, certifying that the user authentic ated
Ticket Gra nting Server (TGS) 5. The client viewer forwards the ticket to the DKS 6. The DKS sends the key for the specific page
3. The client viewer forwards the ticket and asks for a specific key server 4. TGS signs a tic ket if the user is allowed to acc ess the content
Decryption Key Server (DKS)
Figure 3: Content can only be accessed via the digital container's methods
Content cannot be accessed directly but only via specified methods of the container. If the user executes a method such as showContent() the container checks the user's identity, authenticates the user, obtains a service ticket and retrieves a key to finally decrypt the content. Once the content is displayed the key is discarded; thus the content is never stored in an unencrypted way (Figure 4).
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Digital Content Conta iner void showContent() { PromptUserAuthentication (); authenticateUser (); getTGSTicket (); getDKSKey (); decryptContent; displayContent; }
Encrypted Content Viewer Figure 4: After authentication (1,2) and receiving a service ticket (3,4) the container obtains a decryption key to display the content.
The major improvement of this proposal is that the distribution of high volume data can be achieved by P2P technology. Besides obvious benefits concerning download speeds, the advantage of distributed storage also increases availability of relevant data. This basic idea is, for instance, also used by the Lockks [13] system that attempts to create distributed digital libraries and preserve publications through distribution. This system also incorporates a DRM to allow only site (libraries) to store only the data (i.e. publications) that they have subscribed to and paid for. Clearly, without such a system no publishing house would even think about supporting such a system. 4.2. Improvements To make a P2P e-learning system successful it is of paramount importance to address fundamental issues such as the quantity and quality of content and security. Security actually plays the central role of an enabling technology. Many people refrain from using P2P software in professional and academic setting because of security concerns. Only when users can trust the system to fulfil their security requirements will they start using it. 4.2.1. Quantity of Content To be used by people it is essential that a wide variety of content exists. On Kazaa, for example, hundreds of thousand users share terabytes of data. Therefore it is a good idea to base any P2P system on a large user base. So, if for example a P2P network for history teachers one might consider also targeting history students or even everyone who interested in history. 4.2.2. Quality of Content Attempts from the music industry to discourage usage of P2P networks including flooding the P2P network with fake content. A quality rating system – quickly devised – solves the problem. Moreover, a good indicator of the content's quality and genuineness is the number of nodes that currently offer the file. Corrupt files are quickly deleted by most users. As previously indicated quality rating of music or videos is fairly straight-forward. For e-learning content, however, it is not that easy. Perceived quality of the content also depends largely on the user's expectations. Therefore it is essential to correctly classify and describe the content. There are several standardized formats of meta-data such as LOM or SCORM (see section “Related Work”). 4.2.3. Granularity of content Smaller content-units are easier to share than larger ones. Cohesive entities easier fit the demands of learnwilling participants. The structuring of content in reusable entities [1] is also necessary for further introduction of a workflow management system.
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4.2.4. Security Security encompasses many aspects. The biggest thread is certainly executable content or macro enables documents containing malicious payloads. Current antivirus software will prevent infection quite reliably and some P2P client software even comes with anti-virus protection. P2P is often associated with copyright infringements. This clearly is an issue. A DRM that is too prohibitive not only prevents fair use of the content but also ultimately prevents learning. For instance, if users are not allowed to print content, those who better learn from paper-based manuscripts can no longer learn efficiently. Given the usual willingness of academics to share knowledge, we are convinced that a proof-of-origin will suffice. Even if users access content in ways they should not, most academics do not mind as long as everyone knows who originally created the content. Another security concerns pertains to the files that are shared. Users are sometimes afraid that everyone will be able to access all their files – which is obviously not true. Assuming a trustworthy P2P product it is very easy to change which files are shared and which not. It simply involves moving files to and from a shared directory. Today, several P2P software products (e.g. Kazaa) contain spyware. Even though alternatives (e.g. Kazaa light) exist many people still do not trust these systems. We assume the major reason to be the fact that P2P is often used for illegal activities. User who illegally distribute copyright protected music and videos cannot easily complain about malicious software. In an academic setting, given the well-established procedures of peer-based code reviews in the open-source community, it is very likely that a stable and powerful client without spyware can be built. In fact, the Lionshare Project [12] uses Limewire which is available under the Gnu Public Licence (GPL). Being written in Java it runs on different platforms and since the source code is available to everyone, hidden spyware is unlikely to be included.
5.
Critical Evaluation
Clearly, P2P is a buzzword. Before setting up a P2P environment one has to carefully evaluate why P2P could encourage sharing. The Web has been around for quite some while. Personal home pages would be an obvious choice to publish content. Compared to P2P there are several differences. With P2P •
Publishers and distributors can remain anonymous.
•
No Web space is required. The local PC provides the required space.
•
Replication of popular data on various nodes is performed without explicit mirroring
•
Easy to use
When sharing illegal content anonymity may be required but in this paper we do not consider any illegal activities. Even if users are not involved in any law-breaking activities there may still be users you would want to remain anonymous. However, our experience in the (technical) scientific community has shown that researchers and teachers are usually very proud of sharing and want others to see their names. The effort of content production as we think leads to the willingness to share. We therefore conclude that anonymity is of small importance in the context of e-learning. For many users large Web space may not be available. At universities, however, Web space is usually not a problem even though it will most likely not be as large as modern local hard drives in PCs.
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In existing P2P networks we can observe that popular content is available on many nodes. This is due to two facts: First and foremost popular content is per definition downloaded by many people and in most cases downloads are shared per default. Second, since sharing is rewarded by increasing the user’s priority, there is an incentive to share popular content rather than unpopular – assuming disk space is limited. Ease-of-use, the last remaining factor, is clearly a contributing factor. Informal interviews with many teachers (mostly in non-technical subjects) indicate that this is indeed the most contributing factor. The distribution and multiple storage of content aggravate the quality control of shared content. In p2p-networks the success of an update process can’t be guaranteed. A further basic problem in p2p-networks is the missing monitoring on the process flow. Especially in learning scenarios this kind of control is necessary for teachers and tutors to do their job. Courses usually follow a pedagogic elaborated plan. Learning material has to be distributed area-wide in a specific order. Although we propose a p2p approach for e-learning we can’t abandon a server to fulfil the requirements on an e-learning system. Not only has the process-flow needed to be controlled by a central instance. Also the notifications about changes and annotations need to be published from a central instance to grant data-consistence. These functions, however, can be implemented on top of the centralized authentication and authorization system.
6.
Related Work
Since the advent of first computer-based training solutions, reusability and scalability have always been seen as key advantage. To be able to reuse content it obviously is of paramount importance to find what one is looking for. Therefore, various approaches of describing and structuring e-learning content have been proposed. LOM stands for „Learning Objects Metadata“. Since 1997, the IEEE Learning Technology Standards Committee (LTSC) has maintained the standard. The main purpose of the project is to “search, evaluate, acquire, and utilize Learning Objects” and to enable the “sharing and exchange of Learning Objects” [7], [8], [9] SCORM stands for “Shareable Content Object Reference Model”. SCORM is a content model relying on recommendations to keep implementations by the different vendors consistent. SCORM is designed for various aspects such as learning management systems, content authoring tools. It builds upon the work of the AICC, IMS, IEEE, ARIADNE aiming to create "reference model of interrelated technical specifications and guidelines designed to meet DoD's high-level requirements for Web-based learning content.” [1][2]. S. Ternier presented the development of a peer-to-peer (P2P) based tool to share and reuse learning objects. The general idea is to make it easy to publish and search their metadata. The goal of LOMster is to leverage the popularity of file sharing in the context of e-learning content. LOMster uses XML files to store metadata. Its implementation is based on the JXTA P2P Framework. [10]. Edutella [15] – a similar project – uses RDF (Resource Description Framework) as a metadata standard. RDF provides a categorization system to support the exchange of knowledge. Using RDF to describe the content Edutella builds on the technical infrastructure of the JXTA Framework [10].
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According to Ternier et al. [20] users often find it cumbersome to insert new material in a clientserver based repository. They are exploring whether LOMster-like approach may help to overcome this problem. They envision that contributing new material is as easy as dropping the relevant files in the shared directory. Even though this approach obviously reduces the effort required for sharing, it does not take the time to complete metadata into account. Unfortunately, this could result in poor metadata.
7.
Conclusion
This paper explores the benefits that P2P technology may offer to share e-learning content. The paper’s main contribution is to clearly show which features contribute to today’s popularity of P2P. We think that a P2P network will finally succeed to implement the benefits of reusable e-learning components. Sharing content – previously through Web repositories – was one important reason for promoting e-learning. Moreover, the rationale of various classification schemata is to facilitate sharing. It may be only due to the difficulty of using and the required time that Web-based content repositories have not proven as successful as predicated. In our opinion P2P can, if correctly used, overcome these drawbacks and offer what has long been promised.
8.
References
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