Abstract. E-learning technologies have developed greatly in recent ye- .... in the org.dvb.dsmcc package, applications have access to the so-called. DSM-CC ...
A Mixed XML-JavaBeans Approach to Developing T-learning Applications for the Multimedia Home Platform Mart´ın L´ opez-Nores, Ana Fern´ andez-Vilas, Rebeca P. D´ıaz-Redondo, Alberto Gil-Solla, Jos´e J. Pazos-Arias, Manuel Ramos-Cabrer, and Jorge Garc´ıa-Duque Dept. de Enxe˜ ner´ıa Telem´ atica, ETSE Telecomunicaci´ on, Universidade de Vigo, Spain, {mlnores, avilas, rebeca, agil, jose, mramos, jgd}@det.uvigo.es
Abstract. E-learning technologies have developed greatly in recent years, with considerable success, which has suggested extending distance education to other mediums. This paper studies the possibilities of Interactive Digital TV to provide educational services (t-learning) and analyzes the support offered by the Multimedia Home Platform standard (MHP). We also present an approach to developing interactive t-learning courses and a tool, based on public and well-known technologies, that implements our proposal over the MHP technological framework. Our approach is remarkable for being flexible, extensible and easy to integrate with existing standards for the management of learning content, thus promoting interoperability and content reuse. In addition, applications can be developed with no need of programming knowledge. This is essential to free designers from technological details, so that they can concentrate on the broadcast contents, their sequence, interrelations and every aspect that makes up a value-added application.
1
Introduction
In the last decades, there has been growing interest for distance education systems, mainly in developed countries. These systems allow for continuous learning and training, overcoming the main lacks of traditional learning media. Access to knowledge and learning is widely regarded as the best way to maintain a region’s competitiveness, especially in today’s global economy. In recent years, this distance learning necessity has promoted significant development of Internet-based learning initiatives (e-learning). The Internet stands out for its flexibility, but its increasing use has shown several shortages related to difficulties in the use of the computer for some social sectors, limited penetration of computers in homes (ranging from 40% to 60% in Europe) and uneven presence of broadband infrastructure. To solve these shortcomings, some initiatives are being taken to port educational services to other mediums through alternative devices, e.g., t-learning (Interactive Digital TV) or m-learning (mobile devices). All these technologies
are expected to converge in the foreseeable future [1], to accommodate the different needs of the users. Therefore, it is not a question of the computer taking over the television or vice versa: it is a question of how the different services and models converge, increasing value to the consumer. Interactive Digital TV (referred to as IDTV) may be helpful in the goal of developing courses to reach the highest number of people (TV penetration in Europe is almost 99%). It also meets the socially important need to offer online learning services to people who cannot afford to buy a computer, do not have Internet access or lack the knowledge to manage this kind of technologies. But t-learning is not only targeted at homes, because it can be used to offer learning services to enterprises and traditional learning institutions as well. In any case, IDTV success obviously depends on the services being offered to the users. T-learning services may help fulfill a notorious emptiness in the set of engaging applications which TV users are willing to pay for. So, the union of distance learning and IDTV can provide mutual benefits. A multimedia course system as required for t-learning applications involves a large amount of content formats and interrelation capabilities. In addition, the applications must obey the restrictions imposed by the TV standard being used. These technical issues are beyond the tasks of content designers, and it is necessary to provide software tools to support the creation of the courses, allowing designers to concentrate on the contents to be presented to the user instead of on the way they are programmed. The goal of this paper is to present a low-cost development framework for building t-learning courses, based on free technologies, regarding the special characteristics of this medium and promoting interoperability as well as content and software reuse. The rest of the paper is organized as follows: In Sect. 2, we enumerate human, economical and technological implications regarding the possibilities of t-learning as an increased-value service. Section 3 analyzes MHP, the most important standardization initiative currently being taken in the IDTV field. In Sect. 4 we present the master lines of our development architecture proposal. Finally, in Sect. 5 we present some conclusions and future lines of research.
2
Exploring T-learning
In the late 1990s, it was expected that IDTV would experience an enormous growth, but expectancies have not materialized so far. Apart from world-wide economy considerations, we think that the main cause of this slow expansion is the lack of services that users may regard as a necessity. Many people show interest in the services currently offered, but only a small percentage are willing to pay for them. Several mass studies (see [2]) have shown that t-learning is considered to be an interesting service, capable of gathering a number of paying users. In order to successfully exploit this interest, it is essential to take the consumer’s habits into consideration, as long as television has always been an entertainment medium.
Distance learning is a social phenomenon, not a technological one, and potential IDTV users have a lower level of preparation and predisposition to learn new technologies than Internet users. So, a new concept has arisen in this context, edutainment, standing for education and entertainment and meaning the suitable approach to developing models for a less formal learning process. A key issue is that t-learners expect two different forms of interactivity. First, the obvious interactivity with applications, as provided by user interface elements (buttons, menus and the like). Second, and surely most important, is interactivity with people (other actors in the learning system, mainly teachers and other students). This need to interact with other people indicates that feedback mechanisms must be strongly promoted. As a starting point for t-learning, we must take a look at the e-learning field, where extensive research has been done since the mid 1990s [3]. The experience accumulated in developing for the Internet gives some useful theoretical insight for t-learning, as well as a number of standards and tools for content management (see [4]). These standards promote automation and interoperability of contents, and also provide means for creating and reusing pieces of learning via the socalled shared content objects and distributed content repositories, as described in the SCORM [5] and IMS [6] standards. Many of these standards are based on XML, and, although designed for e-learning, they can also be applied to t-learning, as there are no distinctions in content-management requirements. Despite the e-learning experience being useful, there is unavoidable work to be done in order to accommodate the peculiarities of the television environment, such as the following ones: – The running platform is quite different from a personal computer: lower computing power, lower resolution in presentation devices and rather limited user interaction capabilities, as most of the receivers are operated only by means of a remote control. – The fact that TV is usually watched from a higher distance than a computer screen imposes further limits on the size of the elements of an application. – The information distribution mechanisms of IDTV are more complex than Internet ones, mainly because of the packaging of the information and the mandatory signaling of the transport stream. – Internet courses have text and graphics as a central axis, while TV should be based on audio and video in a natural way. This type of media demands greater interrelation between contents and a temporal reference. In addition to technical specifics, the profile of the t-learning users greatly differs from the e-learning ones, which advices against direct translation of the models developed for Internet courses. In this regard, it is necessary to consider that Internet users usually play an active role, promoting the design of userdriven services; on the contrary, TV users have been traditionally passive, which recommends media-driven strategies in the implementation of interactivity. Although the growth of IDTV during the last years has not been as big as expected, there are several running examples of its being used for educational purposes, with USA and UK as leading countries (see [2]).
3
The MHP Standard
The change from analog to digital TV is unavoidable, but also complex and expensive. In order to reduce costs and speed up the transition, it has been necessary to define standards to ensure compatibility and to achieve a market size big enough for operators to recover investments in the short term. In the last decade, the Digital Video Broadcasting (DVB) Consortium has played a leading role in this normalization process, publishing technical standards that have achieved widespread use. In February, 2000, DVB published the Multimedia Home Platform (MHP) standard [7], specifying all the mandatory rules that conforming receivers and interactive applications should follow. The proposed normalization enables content developers to create services that can be broadcast over any network. The aim is to promote horizontal markets, with competition in every level of the business chain. The standard defines two types of applications: DVB-HTML and DVB-J. The DVB-HTML model follows a declarative approach taken from the Internet world, and includes many of its technologies (XHTML, ECMAScript, cookies, etc.), with slight modifications to address the specifics of the television context. It is a vast set of elements that is commonly regarded as too difficult for receiver manufacturers to implement, and too complex for content developers to use [8]. On the other hand, DVB-J applications are written in Java, and are commonly referred to as xlets. An xlet may be viewed as a set of class files and other resources that are broadcast within a service, to be executed by a local Java Virtual Machine. MHP imposes two main restrictions to xlets: they must use only a completely specified set of APIs to implement their functionality; and they must obey a well-defined life-cycle that allows a system entity, the Application Manager, to control their operation. Xlets are delivered as compiled, ready-to-run class files, whereas DVB-HTML applications are tagged files to be parsed and interpreted. This has clear performance implications. In addition, the Java language, enhanced with the extensive set of MHP APIs, is more powerful than its declarative counterpart and provides more specific support for the characteristic features of the IDTV medium. So far, it should be no surprise that we have chosen DVB-J for our t-learning proposal. Next, we analyze some aspects of the MHP APIs closely related to the purposes of this paper [9]. An in-depth description of these and other features can be found at [10]. Asynchronous Loading of Contents. One of the main implications of contents being broadcast as DSM-CC object carrousels (introduced in ISO/IEC 13818–6) is that object classes and data files cannot always be loaded immediately when they are needed, as they may come up with noticeable latency. Synchronous loading of those contents (as done by the java.io package) would prevent other actions from taking place in the meanwhile, making applications slow and surely annoying for the user. This would have great impact on t-learning applications, where many content sources may need to
be displayed at once. Fortunately, the MHP APIs provide for caching in the receiver, and for applications to give indications on how to use it. The corresponding API has methods for both synchronous and asynchronous loading, as well as methods to indicate that a certain file should be preloaded in the cache if possible, because it could be needed soon; or that a certain resource will not be needed anymore, so that it can be flushed from the cache. Synchronizing Applications and Streaming Media. By using the classes in the org.dvb.dsmcc package, applications have access to the so-called DSM-CC stream events, which are markers embedded in the MPEG-2 transport stream, intended to provide applications with one or more temporal references. Each marker can be linked to objects carrying any desired information, making it possible to synchronize applications and streamed media, as required in media-driven strategies. The API provided follows a subscription model, as illustrated in Fig. 1.
subscribe() StreamEventListener
DSMCCObject receiveStreamEvent() receiveStreamEvent()
MPEG-2 Transport Stream
time markers
Fig. 1. The subscription model for synchronization with streaming media
The Return Channel. MHP defines several receiver profiles, and only the simplest one (“enhanced broadcasting”) does not support a return channel. Where available, it can take any form (such as cable, PSTN or ADSL), but is always accessed by the well-known java.net classes. A number of transport protocols may be used, including TCP, UDP and service-specific ones. The use of a return channel may be essential for some services, especially some t-learning ones. Applications can specify their hardware requirements, so that if they are not met at a particular receiver, those applications are not offered to the user. The return channel provides rich interactivity, and it can be used for several purposes: student tutoring and evaluation, additional consultations from Internet sites or online discussion forums involving teachers and students. One step further, multiconference systems, with cameras on the user’s side, would greatly improve the learning experience.
4
Our T-learning Applications Development Approach
In order to provide the highest degree of flexibility, we have designed a simple, non-restrictive structure for the courses. They are just sets of pedagogical units (PUs), and those units define most of the application’s logic. Pedagogical units can contain any kind of components (text, graphics, audio and video clips, etc.), that can be laid out in multiple sub-units 1. Units can be designed as media-driven or user-driven, depending on whether the user’s role is expected to be more passive or active, respectively. User-driven units are typical in e-learning schemes, while media-driven ones further exploit the multimedia capabilities of IDTV and cover the traditionally passive role of TV users. Mediadriven strategies are, by far, the most suitable approach for edutainment. Our approach for developing t-learning applications has several remarkable features that make it different from existing e-learning frameworks: – As for any distance learning system, we provide mechanisms for conditional access. This refers to the fact that, in many cases, one student should not go on browsing units if he/she has not proved some knowledge in the preceding ones. In e-learning schemes, it is usually the server who decides whether access is granted or forbidden. On the contrary, in t-learning this must be decided at the receiver, because the broadcast channel is one-way and there might be no return channel. – Similar comments apply to the use of templates when designing applications. This is a common feature for many e-learning development tools, but the delivery mechanisms of IDTV make suggestions on how and when templates are configured, in order to optimize bandwidth requirements and reduce latencies by improving the effectiveness of caching policies. – The large amount of content formats and the predominance of multimedia contents demand great interrelation capabilities among multiple sources of information. Thus, we have devised a mechanism for contextual binding, which is also used to achieve synchronization between application data and the underlying media streams, as required by media-driven units. 4.1
Defining the Structure of the Courses
The configuration of a course determines the sequencing of the pedagogical units, the order of the scenes that make up the units and the interrelations among them. As earlier described, a media-driven approach is desirable for interactivity in t-learning courses. To this aim, active entities must exist to keep control of content presentation and user interaction. We have defined every content element included in a given scene as an active entity, controlled by a manager responsible for changing its properties, starting and stopping reproduction, etc. 1
Sub-units can be classified as views or scenes, depending on the application. The term view is more suitable for the arrangements of the elements in user-driven units, while the term scene is preferable for media-driven ones.
The scenes in a PU are controlled by the PU Manager, which handles user input, context synchronization and communication with other PUs. Finally, all the PU Managers are coordinated by a Course Manager, the highest authority in course execution, that is in charge of loading the PUs and setting their parameters. These global relations can be observed in Fig. 2.
Course Manager Pedagogical unit
Pedagogical unit
Pedagogical unit
PU Manager Scene textMan.
Scene graphMan.
videoMan.
Fig. 2. Course structure for a media-driven interactivity approach
The Course Manager is also in charge of the conditional access mechanism. At any moment, the PUs can be locked (access forbidden) or unlocked (access granted). This locked/unlocked state of an unit can be changed by actions related to components in that unit or any other one, in a way that unlocking can be associated with events such as passing a certain test. These events are gathered and handled by the Course Manager. In our scheme, the Course Manager is the MHP application itself. It is built as an xlet that, when initialized, reads the name of an XML configuration file from its associated context. The file describes the composition of the course, and determines the rest of the Course Manager’s actions, starting with the first unit to be loaded, set up and displayed. 4.2
The Use of Templates
Our development approach promotes the use of templates for pedagogical units. Everything that is common for several units can be saved as a template that will be instantiated and parameterized to create them, with no need to modify or recompile any source code. Configuration parameters are stored in XML files.
Our approach to templating differs from those of other applications in two fundamental aspects: – Templates can be configured out of the program in which they were created, allowing for configuration to take place at the receiver. On the contrary, for example, typical applications for creating slide-shows also use templates, but these can only be configured within the program itself. – Configuration takes place at runtime, and not at design time (see Fig. 3). This has a clear advantage in the MHP environment, because this way only one class file has to be inserted in the object carrousel, whereas the alternative would require one different class file for each pedagogical unit, regardless of how similar they are. The XML configuration files of the pages have to be broadcast as well, but they are usually considerably smaller than class files representing complete units.
PU template Template repository
Multiple scenes
Fully specified PU XML file
Runtime configuration
Fig. 3. Runtime configuration of templates from XML files
The alternative option (configuring templates at design time) is typical in e-learning scenarios: once the contents have been selected, convenient HTML pages are created. This approach makes sense on the Internet because resources are downloaded on demand. Doing the same in an IDTV environment would result in bandwidth squandering and, most important, in increased latencies, because object carrousels would get crowded with bigger objects, reducing the number of resources that could be kept at once in the cache. 4.3
Contextual Binding
When displaying several informational resources, they commonly refer to a same set of topics. In such a case, it is desirable to keep them in touch so that, for example, as the user browses a text file, images illustrating the subject are
changed accordingly. This need to interrelate pieces of information extends to all types of media. It is also the key to synchronization with the media streams, as required in media-driven strategies, in order to support features such as the reproduction of a video controlling the sequencing of the scenes. We handle all these bindings by means of contexts. When a context change occurs in an element of a pedagogical unit, the corresponding PU Manager tells the rest of the elements to switch to the new context, and changes the current scene if so designed. Some of those elements might not recognize the new context and do nothing, while others would take appropriate actions. To achieve synchronization with streaming video and audio, context changes are notified in response to markers embedded in the transport stream, as explained in Sect. 3. Contexts always have an associated context name, and are delimited differently for the different types of media (using timestamps for video clips, anchors for text files, etc.). In any case, the decomposition of information in contexts is saved in XML files, with syntax defined ad-hoc to accommodate the type of media. Most commonly, these files will be created by extracting information from content-management systems. Although the distinction between media-driven and user-driven units is clear, actually the approach should always be mixed. This is to leave, at least, minimum control over the application’s flow in the user’s hands. Designing units either way depends on which events are handled and what contexts are defined. 4.4
The Development Framework
Several tools have been developed to help in the task of programming applications for IDTV. In our experience, none of them turned out to be suitable for t-learning purposes. In some cases, we noticed lack of flexibility due to extreme ease-of-use, as in the case of Sublime’s ITV Suite [11]. Other tools, such as Alticast’s AltiComposer [12] and SnapTwo’s GEAR [13], are intended for general applications and provide no suitable support for t-learning. A common problem with most of the existing tools is that they are based on expensive proprietary solutions tying content developers to use one company’s programs all along the developing process, and also making it difficult to communicate with standard content-management systems. Keeping this in mind, we have created our t-learning specific tool on the basis of two standard and freely available technologies: XML [14] and JavaBeans [15]. XML. XML is an increasingly accepted technology for use in a wide range of applications that entail structuring, exchanging and processing information. We use it to express all those entities with a more or less predefined structure, such as the specification of parameters for templates and the decomposition of pieces of information in contexts, among others. As stated in Sect. 2, a number of standards for the management of e-learning content are also based on XML. This interoperability simplifies content reusing tasks, and greatly reduces development costs. As an example, tests can be automatically generated from databases instead of having to create each and every question manually in the visual builder tool.
JavaBeans. A Java bean is a reusable software component, subject to certain naming conventions, that can be manipulated in a visual programming environment. Beans are used as building blocks when composing applications. In addition to designing the layout of an application, the interrelations among the different components can also be defined in a visual way, automatically binding events and the actions to be taken. Beans can be laid out and connected in order to make up the pedagogical units, making it possible to build arbitrarily complex compositions. Any other approach would require huge amounts of meta-information to achieve the same flexibility. Of course, processing all that information would be timeconsuming, while PUs generated with JavaBeans can be distributed as compiled, ready-to-run class files. Moreover, they can also be saved as general templates for later use, providing for software reusability. We have developed a set of specialized beans, taking into account the commented considerations about the characteristic features of the IDTV environment, ranging from extensions to the user interface elements to context-aware objects managing access to and representation of multiple media resources. Due to the possibly limited resources of the receivers, visual beans are programmed so that, when they are not visible, they automatically minimize their memory needs and stop any running threads they have created. In order to reduce the effect of latencies, resources are loaded asynchronously, with convenient indications being given to the caching subsystem to prefetch some of them. To make it possible for templates to be configured from an external XML file, its elements must provide means for being referred to. That is why we have developed all the necessary beans having a name property, so that an element that is given a name is automatically exported for external configuration. The Course Manager is responsible for finding the elements to be configured at runtime and setting the specified attributes. It is done by using the Java reflection mechanism and has low performance costs. Moreover, this solution provides for separation of content from graphical appearance, because different templates whose beans are named the same way may be configured from the same files, as illustrated in Fig. 4, in which an XML file describing a multiple-choice test is applied on two templates defining different layouts. Our Development Tool. The use of standard technologies promotes interoperability, as well as content and software reuse. On one hand, several sets of beans from different vendors can be used in any JavaBeans-aware development tool. On the other, there are also plenty of applications for handling XML content. However, the task of developing t-learning applications has further requirements. To abstract developers from technological issues, there should be no need to use different tools during the development process: one to design the layouts and several others to import content, etc. This is why we have developed an end-to-end, integrated environment, providing support for all of the features in our development approach, including the following:
Fig. 4. Configuring distinct templates from the same XML file
– User interfaces and layouts for templates and pedagogical units can be created by visual manipulation and drag-and-drop operations. – The XML files containing the decomposition of pieces of information in contexts can be created with editors designed ad-hoc for the different formats. – An editor deals with the composition of the course, defining the ordering of the pedagogical units and the conditional access dependencies among them. – There are wizards, at an initial stage of development, to import the courses’ contents from standard content-management solutions. One of these wizards allows for automatic creation of multiple-choice tests, involving any kind of elements (text, graphics, video clips, etc.) in questions and options, with any desired layout. – It is possible to mark up the media streams in order to synchronize media and application data, which is essential for media-driven units. – The packaging and signalling of the courses is controlled automatically. Our implementation is based on the NetBeans Platform [16], which offers a quite convenient framework to create development environments for nearly every conceivable application. As an example, SnapTwo’s GEAR is delivered as a NetBeans module.
5
Conclusions and Future Work
IDTV’s success greatly depends on new services arising, capable of creating necessity in the users. According to several mass studies, t-learning is widely regarded as one of such services, and the MHP specification offers a quite satisfactory platform for it, as we have studied through this paper. We have presented the master lines of our approach to developing t-learning courses, and also the functionalities of a tool aimed at supporting the development of these applications. The specific characteristics of IDTV, technological
ones and those derived from the users’ profile, advice against direct translation of previous experiences in e-learning and recommend a media-driven approach when implementing the interactivity features. This fact has greatly conditioned the course structure we have proposed. Our approach is based on freely available technologies. JavaBeans is suitable for visual development, and XML is surely the best choice for everything related to information structuring and exchanging. Thanks to the use of these standard technologies, our approach stands out for its low cost, flexibility and interoperability with content-management standards. Some future lines of research can be suggested, including the following ones: – Allowing IDTV learners to make hand-written or voice annotations, highlight phrases in texts or insert markers in videos. This may require introducing new input devices to extend the possibilities of the remote control. – Devising an extension to the proposed architecture in order to facilitate the development of distributed services, promoting interactivity among users to allow for the establishment of virtual learning communities. – Exploiting new ways of using the return channel that are to be opened with the spread of cable and ADSL technologies. This will be the starting point for quality multiconferencing systems. – Further working on efficient and effective metadata architectures intended to communicate with content-management solutions.
References 1. Lytras, M. et al.: Interactive Television and E-learning Convergence: Examining the Potential of T-learning. ECEL 2002, The European Conference on e-learning, Brunel University, (2002). 2. PJB associates: A Study into TV-Based Interactive Learning to the Home. http://www.pjb.co.uk, (2003). 3. Alexander, S.: E-learning Developments and Experiences. Education and Training, 43 (4/5), 240-248, (2001). 4. Clarke, P. et al.: Knowledge Management and Collaboration. Proceedings of PAKM 2000, Basel (Switzerland), (2000). 5. SCORM: Shared Content Object Repository Model. http://www.adlnet.org (2002). 6. The IMS Project. http://imsproject.org, (2002). 7. DVB Consortium: The Multimedia Home Platform. http://www.mhp.org, (2001). 8. Gil, A. et al.: Surfing the WEB on TV: the MHP Approach. International Conference on Multimedia and Expo. Lausanne, Switzerland, (2002). 9. Gil, A. et al.: Exploring T-learning in the MHP Context. IADIS International Conference WWW/Internet. Lisbon, Portugal, (2002). 10. Morris, S.: The MHP Tutorial. http://www.mhp-interactive.org, (2002). 11. Sublime. http://www.sublimesoftware.com, (2003). 12. Alticast. http://www.alticast.com, (2003). 13. SnapTwo. http://www.snaptwo.com, (2003). 14. W3C: Extensible Markup Language (XML). http://www.w3.org/XML, (2000). 15. Sun Microsystems: The JavaBeans Specification. http://java.sun.com/products/javabeans, (1997). 16. The NetBeans Platform. http://www.netbeans.org, (2003).
