A Mixed XML-JavaBeans Approach to Developing t-Learning Applications for the Multimedia Home PlatformMartn Lpez NoresDepartment of Telematic EngineeringUniversity of Vigo (Spain)First International Workshop onMultimedia Interactive Protocols and SystemsMIPS 2003November 18-21, 2003 Napoli (Italy)

OrganizationIntroduction to t-learning.The MHP standard.Solutions for broadcast services.Implementation details.Summary and future work.

A Few Words about t-Learning

A lot of work is being done on distance learning.In order to overcome the limitations of traditional learning.Access to education is considered key to maintain a regions competitiveness.Introduction

IntroductionSeveral major technological approaches have been defined.

The future points towards convergence.Obstacles: networks, interoperability and users.Currently, the different mediums demand different solutions.

t-Learnings Advantages...There is at least one TV in nearly 100% of households in developed countries.Internet not expected to go beyond 70%.Television is easy to use for everybody.IDTV helps to prevent social exclusion in the access to education.Overcomes economical and cultural barriers.No need to buy a computer.No need of technological knowledge.

... and PeculiaritiesA set-top box is not a computer.Lower computing power.Limited user interaction capabilities.A TV screen has low resolution. Simple user interfaces with big visual elements.IDTV is a natural medium for broadcast and handling multimedia content.Users are predominantly passive.TV is considered as a medium for entertainment.IDTV is ideal for informal learning (edutainment).

Strategies for InteractivityApplications respond to the users actions.Typical in e-learning services.The evolution of pieces of media guides users and controls the flow of applications. Main option for t-learning.User-drivenMedia-driven

The MHP Standard

The Multimedia Home PlatformPublished by the DVB (Digital Video Broadcasting) Consortium in February, 2000.It defines a neutral framework for IDTV applications and services.Increasingly popular among broadcasters and relevant enterprises.Initially European ones.The recent GEM (Globally Executable MHP) specification prepares the way into the USA and Japan.

Communication IssuesCommunication in IDTV is highly assymetric.Broadcast networks and (optional) return channels.The MHP framework:MPEG-2 transport streams for broadcasting live audio and video, and DSM-CC object carrousels for other resources.TCP/IP and service-specific protocols for the return channel.The availability of a return channel determines the interactive capabilities.Simulated and real interactivity.

The Object CarrouselMain mechanism to broadcast data in MHP.A group of files transmitted in a cyclical way. A read-only filesystem over an MPEG-2 transport stream.Resources are not always available immediately when needed.There may be noticeable latencies.

The Problem of LatenciesLatencies can be extremely annoying.Example:520 KB @ 256 Kbps = 16 seconds per cycle !Nobody would wait so long for a program to start.MHP offers several ways to control latencies:Caching, preloading and asynchronous loading of contents.Other contributions:Adequate planning of the carrousels.Careful construction of the applications.

The MHP ProfilesMHP defines several receiver profiles.Features and cost tailored to the services required.

We pay special attention to broadcast services.Inexpensive and fast to develop.Suitable for edutainment.Interactivity may drive users towards more active profiles in their use of TV. Extensions for e-mail and web browsingInternetaccess Return channel for real interactivityInteractivebroadcastSimulatedinteractivityEnhancedbroadcast

Principles of the Architecture

Structure of the Courses

Conditional AccessUnits have a locked/unlocked state.Can be changed in response to any event.The composition of a course is summed up in a directed graph, definingThe ordering of the units.The access dependencies.This information must be available at the receivers.Local take of decisions.

Contextual BindingA simple and effective solution for the synchronization of multiple sources of information.Including the broadcast streams (media-driven units).It is based on contexts.Identifiers linked to pieces of information.Defined differently for the different types of content.Timestamps in fragments of audio and video.Regions in images.Anchors in a text.Options in menus, etc.

Templates (I)Templates are a common feature in many development tools.Make development tasks faster.Enhance software reuse.Help to separate content from graphical appearance.Their use in IDTV applications offers additional advantages.

Templates (II)Templates are configured during runtime.Not at design time.

The cost of runtime configuration is masked by latencies and loading times.

Templates (III)The object carrousel transportsthe Java class file of the template,much smaller XML configuration files.Advantages:More files can be kept in the cache.Higher efficiency. The size of the carrousel decreases.Lower round-trip time lower latencies.

ImplementationDetails

Design GoalsNo need of programming knowledge.Flexibility and support for all the phases of development.Based on free, open technologies.Low cost.Extensibility.Interoperability.

Types of ApplicationsApplications programmed in Java.Two main restrictions:MHP APIs.Xlet lifecycle.A declarative language, based on Internet standards.XHTML, CSS, cookies, etc.DVB-JDVB-HTML

Foundational Technologies: XMLA standard syntax forthe composition of the courses,the configuration files for a template,the definition of contexts in the different types of information.Also used when assembling pedagogical units.To communicate with content-management systems.SCORM, IMS, etc.

Foundational Technologies: JavaBeansA components architecture for Java.Promotes components reuse.Provides for visual development.Beans are building blocks to construct applications.Interrelations handled by means of event adapters.Enough for simulated interactivity.Not for non-broadcast services.

A CASE Tool for t-LearningWe have implemented our approach on top of the NetBeans Platform.Features:Entirely visual development.Simple assembling of pedagogical units.By retrieving content from repositories or creating it ad-hoc.Several wizards and assistant tools.To define the composition of the courses.For the automatic creation of multiple-choice tests.To delimit contexts in the different types of information.Automatic generation of the transport streams.

Summary and Future Work

Main ConclusionsHuman and technical factors advice against direct translation of e-learning solutions.Broadcast services are essential at an initial stage.Preparing the way towards highly-interactive services.The MHP standard provides a satisfactory platform.Simulated interactivity.Latencies.Predominance of multimedia contents.Essential distinction between user-driven and media-driven strategies.

Future WorkExploit the power of the return channel.Real interactivity with applications and other users.Personalization of contents.Creation of virtual learning communities, involving people with shared interests.Analyze new multimedia formats: MPEG-4.

End

Good morning. My name is Martn Lpez, and I am here to give you a brief introduction to the work we are doing at the University of Vigo, regarding applications and services for Interactive Digital Television.This presentation deals with our approach to the development of educationalservices.The presentation is organized as follows.We begin by discussing the advantages and peculiarities of t-learning,that is, the provision of educational services on Interactive Digital TV.Next, we give a short overview of the MHP standard, which is the mostimportant normalization initiative in the IDTV field nowadays.After that, we comment some of the specific solutions needed for t-learningservices, especially considering the implications of broadcasting. This isfollowed by some details about the implementation of our approach.The presentation finishes with a summary of the main conclusions, and adescription of what we are currently doing, following the work presentedhere.So, we begin with a few words about t-learning.We all know that there is a lot of work being done on distance learning, in order to overcome the limitations of traditional learning, mostly related toits being rather unflexible.

The importance of distance learning is stressed because access to education is a key to maintain a regions competitiveness, especially in thebackground of a global economy. In this context, the goal is to make learningaccessible to the largest number of people possible.To provide for this need, several major technological approaches have beendefined. The first is e-learning, that is, the use of personal computers toaccess educational services on the Internet. The others are t-learning,supported by Interactive Digital TV, and m-learning, based on the use ofmobile devices, such as PDAs.

The future trend in education points towards convergence of all these mediums, leading to a lifelong and ubiquitous learning experience. However, there is still a long way to go, because of the different networks and protocolsinvolved, the still limited interoperability of applications and contents and,above all, the different profiles, contexts and learning needs of the users.As a result, nowadays, the different mediums promote and demand differentsolutions.For the rest of the presentation, we will concentrate on t-learning, and webegin by commenting its advantages. First, there is at least one TV in nearlyevery household in developed countries, while the penetration of the Internetis not expected to go beyond 70%.

Furthermore, television is easy to use for everybody. As a result, IDTV helpsto prevent social exclusion in the access to education, overcoming botheconomical and cultural barriers. First, because there is no need to buy acomputer to access t-learning opportunities; and, second, because no technological knowledge is needed.T-learning also has several technical and human peculiarities that make itdifferent from e-learning.First, a set-top box is not a computer. It has lower computing power and morelimited user interaction capabilities, because it is usually operated only bymeans of a remote control.In addition, a TV screen has much lower resolution than a computer screen,which conditions the design of user interfaces.IDTV is also a natural medium for broadcasting and handling multimediacontent.Finally, it is important to note that TV users are predominantlypassive, while Internet users commonly play an active role. Television hasalways been regarded as a medium for entertainment, and so IDTV isideal for informal learning, that is, edutainment, a kind of educationthat has proved pedagogical value.

The commented aspects suggest a distinction between user-driven andmedia-driven strategies to provide interactivity. In user-driven strategies,applications respond to the users actions, which is typical in e-learningservices.

On the other hand, in a media-driven strategy, the evolution of a piece of audio or video guides users, and also controls the flow of applications.Because of the passive role of the users and the predominance of multimediacontent, media-driven strategies are the first option for t-learning, at least in the short-to-medium term.We now take a look at the MHP standard, commenting those aspects that condition the development of t-learning services.The MHP standard was published by the Digital Video Broadcasting group in February, 2000. It defines a neutral framework for IDTV applications andservices, that is becoming increasingly popular among broadcasters and otherrelevant enterprises. It was first adopted in Europe, but now it is getting intothe American and Japanese markets as well, because of the GEM specification,with GEM standing for Globally Executable MHP.The most remarkable fact in IDTV nowadays is that communication is highlyassymetric between service providers and users. Most of the content isdelivered via broadcast, leaving return channels as an option.

Broadcasting in MHP is based on the use of MPEG-2 transport streams forlive multimedia content, and object carrousels for other resources, such asimages or Java classes. On the other hand, the return channel is mostly operated by means of the TCP/IP suite of protocols.

The important fact here is that the availability of a return channel determines the interactive capabilities, leading to a distinction between simulated and real interactivity. It is simulated when it is only possible to interact with contents in the transport streams, and it is real when the user can actively interact with service providers and other users.Object carrousels are the main mechanism for broadcasting data in MHP, and their use has several implications regarding our purposes.

A carrousel is a group of files that are transmitted in a periodical way, offeringthe view of a read-only filesystem on top of the transport stream.Cyclicality implies that resources cannot always be loaded immediately whenthey are needed. On the contrary, there may be noticeable latencies.

And these latencies can be a major headache for application developers.For example, a carrousel holding 520 kilobytes of information may typicallyneed 16 seconds to complete a cycle. Obviously, nobody would wait so longfor a program to start, or for a given resource to be displayed.

Fortunately, the MHP standard provides several ways to control latencies, such as caching, preloading and asynchronous loading of content.Other contributions to alleviate the problem are possible, including theadequate planning of the carrousels, and several ways to optimizeapplications, that I will explain later.The MHP standard defines several receiver profiles, in order to tailor features and cost to the services required.Enhanced broadcast is the only profile lacking a return channel, so it merely provides for running multimedia-rich applications based onsimulated interactivity. Interactive broadcast introduces a return channelto provide for real interactivity, and the Internet access profile extendsthe latter with capabilities for e-mail and web browsing.

The architecture for t-learning services that we propose here pays specialattention to broadcast services, because quality return channels are not yetavailable everywhere. So, our aim is to exploit the capabilities of Enhanced broadcast.

Broadcast services are inexpensive and fast to develop, because nothing butthe already existing infrastructure is needed. In addition, they are suitable for edutainment, and are also important because their interactive features may drive users towards more active profiles in their use of the medium, bringingup new service and business opportunities.Now, we are going to discuss some of the principles of our architecturefor t-learning services.In our approach, educational services are built as courses, consisting on a set of pedagogical units. These units can be made to resemble different subjects of the national curriculum, for example.

Access to the units is controlled by an entity called the Course Manager, thatmakes it possible to reject access to one unit until some knowledge has beenproved on the preceding ones.

The internals of the units define most of the applications logic. Theirelements can be laid out in multiple scenes, and any kind of interrelations canbe established among them. This is, for example, to make a button start avideo when pressed.

A special kind of interrelation is needed to keep different pieces of media synchronized. For example, as the user browses a text file, images illustratingthe subject should be changed accordingly. For the sake of scalability, this type of binding is controlled by an unique entity, called the Unit Manager.In order to provide for conditional access, units have a locked/unlocked state,that can be changed in response to any event, such as passing a certain test.

The composition of a course is expressed in a graph, defining theordering of the units and the access interdependencies among them. In thesimple graph on the right, we see a course made up of three units in which,to be given access to a certain unit, all the previous ones have to be unlocked.

Because there may be no return channel, all the information aboutconditional access has to be available at the receivers, to permit a local take of decisions by the Course Manager.Now we describe contextual binding, the solution we propose for thesynchronization of multiple sources of information, including the audio and video streams, as required by media-driven strategies.

Our solution is based on contexts, that is, identifiers linked to pieces ofinformation, which are defined differently for the different types of media.For example, they are delimited by timestamps in fragments of audio andvideo, by regions in images, etc.

Synchronization works in a very simple way: whenever an element of an unit detects a context change, it notifies the corresponding Unit Manager, whichpropagates the change to the rest of the elements. Then, each element that recognizes the new context switches to it by taking appropriate actions.The last mechanism we will comment refers to the use of templates to build applications. This is a common feature in many development tools, becausethey make development faster, enhance software reuse and also help toseparate content from graphical appearance.

We will see now that their use in the IDTV environment can provide someadditional advantages.The important fact about templates in our approach is that they are configured during runtime, and not at design time, as is typical in e-learningscenarios.The parameters are stored in XML files, and applied by means of reflection.The cost of doing is masked by the effect of latencies and loading times.

Our approach is advantageous, for example, when the same template is used for several units, which is common practice.In this case, the object carrousel transports the Java class file of the templateand XML files containing sets of parameters for it.The interesting point is that these files are usually much smaller than complete Java classes, typically in a one to ten ratio.

This results in several advantages. First, because files are smaller, more ofthem can be kept in the cache at once, leading to a higherefficiency. Moreover, as the size of the carrousels decreases, they becomefaster and therefore provoke lower latencies.Now, I will comment a few details regarding the implementation of the commented approach. We have created a CASE tool to assist in thedevelopment of broadcast t-learning services, for which we initially fixed the following design goalsThe first was that it should be possible for a non-expert to create courses.It was also important to provide a flexible tool, offering support for all the phases of development.

Finally, the implementation should be based on free and open technologies, in order to come up with a low-cost and extensible solution. Furthermore,interoperability is also a concern, especially towards future convergence withother mediums, as commented before.The current version of MHP supports two types of applications. First,DVB-J applications are programmed in Java, with restrictions regarding theAPIs they can make use of and the lifecycle they must implement.On the other hand, DVB-HTML applications are programmed ina declarative language, taken from the Internet world.

Both models have similar capabilities, but DVB-J is more flexible, ellegant,extensible and even easy to understand, so we have chosen it as the basisfor our implementation.The first of the foundational technologies chosen is XML, which providesa standard syntax for the composition of the courses, the configuration filesfor the templates, and the definition of contexts, among others.

Furthermore, XML is used when assembling pedagogical units, in order toretrieve content from repositories such as those defined by the SCORM andIMS standards.The second foundational technology is JavaBeans, an architecture of components for Java that promotes reuse and facilitates visual development.

Beans are basic building blocks with which to construct applications. The interrelations among them are handled by means of event adapters, that bindevents in the source object with the actions to be taken in the target ones.

The mechanism of event adapters suffices for simulated interactivity,provided that beans offer a rich interface. However, non-broadcast services demand ways to define complex interaction patterns among thedifferent users, and complex actions to be bound to particular events.We have implemented our approach on top of the NetBeans platform, and our development tool currently offers the following features. First, applications can be developed in an entirely visual way, with no need to write a single line of code. Pedagogical units can be assembled in a very simple way, by retrieving content from repositories or creating it ad-hoc. There are several wizards, assisting the developer to define the compositionof the courses, to create multiple-choice tests, and to delimit contexts in thedifferent types of information.Finally, our tool also generates the transport streams automatically, with options to optimize the performance of the carrousels.

Here, we can see a snapshot of our wizard to define contexts in videos, which offers the typical buttons for playing, pausing and stopping, and also the possibility to save the decomposition in an XML file.

In this other example, we see the effect of applying the same XML file defining a multiple-choice test over two different templates, that name theirelements the same way, but define different looks and layouts, contributingto separate content from graphical appearance.

To conclude, I will now summarize the main ideas of the presentation,and also suggest future lines of work, some of which we are currentlyundertaking.We have seen that there are both human and technological factors that maket-learning different from existing e-learning solutions, and so it needs someparticular attention. In this regard, broadcast services play a leading rolebefore highly-interactive services can be massively deployed, that require larger investments.

We have also seen that the MHP standard provides quite a satisfactoryplatform for t-learning, with some mechanisms addressing the mainconcerns of broadcast services, such as the presence of latencies and thepredominance of multimedia content.

Finally, we have suggested that there exists and essential distinctionbetween user-driven and media-driven strategies for interactivity.The work we are doing now deals with the adequate exploitation ofthe return channel in order to develop highly-interactive and personalized services. We resort to peer-to-peer techniques, in order to promote the creation of virtual learning communities that involve people with commoninterests.

Another concern deals with analyzing the impact of new multimedia formats,not currently supported by the MHP standard. We concentrate on the MPEG-4 standard, which we consider to be a main actor for thefuture of all multimedia applications and services.And this is the end of the presentation. If you have any question, I will tryto answer them as well as my English permits. Thank you very much for yourattention.