Application Control Management in Active Spaces Using the ActivePresentation Infrastructure Mark Stroetzel Glasberg and Renato Cerqueira Tecgraf - Computer Graphics Technology Pontifical Catholic University of Rio de Janeiro Rua Marqus de S˜ao Vicente, 225 ITS - Gvea Rio de Janeiro, RJ, Brazil {mark,rcerq}@tecgraf.puc-rio.br

Abstract As the cost of computer devices decreases, work environments become increasingly more sophisticated and complex to administer, and a need for integrating software to simplify the use and to better explore the potential of those environments grows. In this article, we present a software infrastructure called ActivePresentation to assist the construction of synchronous collaborative work applications. We discuss some of the challenges faced in the construction of such applications and introduce the ActivePresentation infrastructure, describing a few prototypes. Additionally, we explore the idea that, with the aid of a multimedia document, ActivePresentation could be used to orchestrate a distributed multimedia presentation. Finally we discuss some related works. Keywords: Collaborative Work, Distributed Multimedia Applications

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Introduction Evident computational progresses such as greater processing power and storage space, larger network bandwidth,

new wireless technologies, longer lasting batteries and lower power consuming processors are making computers more integrated to everyday life, and a model called ubiquitous computing [1, 2, 3, 4] is being discussed for some 1

years now. More frequently than ever, workrooms are being populated with many and varied computer devices. Planned for meetings, workgroups and conferences, these rooms are designed to execute multimedia presentations composed of video, sound, static images, web pages or even conventional applications which are not directly related to multimedia content. Nevertheless, these workrooms suffer from a lack of resource integration that makes them hard to use and ends up wasting the potential that their integrated usage could bring [5, 2, 3]. The under-utilization of such rooms can also be observed in cases of distance collaboration, that is, when teams in different locations try to cooperate during a work session. Typically, collaboration mechanisms are restricted to videoconference systems, which provide limited interaction between participants. Besides, the images captured by videoconference systems do not offer satisfactory quality, requiring better image resolution and therefore bigger bandwidth. We present in this article an additional solution for videoconference systems that tries to simplify the utilization of applications in this new type of environment. The ActivePresentation infrastructure offers a low bandwidth solution, providing easy distributed control over open-source or proprietary applications in heterogeneous environments. Its control and integration mechanisms make the infrastructure appropriate for building applications to either execute synchronous collaborative work or run distributed multimedia presentations. This article is organized as follows: in section 2, we analyze some characteristics and challenges of developing applications for multifunctional workrooms under the paradigm of Active Spaces [2]; in section 3 we present the ActivePresentation infrastructure, explaining some choices made and the project’s basic architecture; section 4 shows prototypes of applications built over this infrastructure; section 5 analyzes some related works, commenting on and comparing their goals and solutions; finally, section 6 ends the article with some conclusions and future works.

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Active Spaces and Multifunctional Workrooms Ubiquitous computing environments are composed of a large variety of communication and computational devices

that add to the perception and activity of the user providing information and digital processing. Computer devices are now widely available, offering new functionalities and increased productivity, making most everyday tasks easier. At home, at work or in public areas, a ubiquitous computational infrastructure is capable of optimizing the user’s environment in response to his working and entertaining activities. Users can have access from any location and at any instant to the network and to the computational resources. In a ubiquitous-computing context, applications must be able to effectively use the available resources and sup2

port user activities. However, while the heterogeneity and the number of devices present in workrooms potentially increase interaction and productivity, they demand great integration efforts. In order to promote the development of applications for such environments, Gaia [2] has defined the concept of Active Spaces, which extends the physical space by means of computational devices and software infrastructure that manage the resources available and coordinate the activities happening in such space. This software infrastructure plays a role similar to an operating system in a conventional computer, defining a new computational environment that converts a physical space and its devices into a programmable system. An example of an Active Space hardware configuration that has become increasingly common are multifunctional workrooms. Such rooms are work environments that combine a series of computational resources that support activities such as meetings, presentations and collaborative work sessions. These activities can happen either with all the participants present in the same work environment, with some remote participants or even with all participants distributed in different locations. Therefore, it is frequently necessary to integrate and control the resources of multiple workrooms. According to the Active Spaces philosophy, this kind of situation would be equivalent to a network of Active Spaces, which could be called a Super Space. When dealing with multimedia presentations, the variety of resources available in workrooms could be used to render different contents through the many devices instead of using only one big screen. Similarly, such contents, or at least part of them, could be presented simultaneously in devices located in other rooms or even in a personal computer of a remote participant. This type of work environment naturally allows for cooperative work, in which many users interact simultaneously with the environment, either locally or not. Works such as [2, 3, 6] offer a generic infrastructure for the development of applications for Active Spaces. In addition to such systems, the use of software infrastructures specialized in certain application domains can facilitate the development of user applications. In the next section, we will present an infrastructure called ActivePresentation, which has the purpose of providing basic mechanisms for the development of collaborative applications and multimedia presentations for resourceful workroom environments.

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The ActivePresentation Infrastructure A thorough use of a multifunctional workroom during either a multimedia presentation or user interaction must

contemplate multiple inputs through different devices. To deal with multiple input and output interfaces of the many devices present in such rooms, the system needs some degree of autonomy, either by means of a system to capture user intention [3] or by somehow programming of the use of the environment [2, 6]. 3

The construction of such autonomous systems relies on the communication among devices, the exchange of information such as files and messages among applications, the availability of computational resources (software and hardware) and the state of running applications. Such functionalities are typically provided by Active Space Middleware such as Gaia [2], Aura [3] and BEACH [6]. The ActivePresentation infrastructure presented here does not intend to be an Active Space middleware, but rather to complement such systems by organizing and structuring applications that do cooperative work or execute distributed multimedia presentations. However, in order to focus on the main goals of this work, we opted not to use an Active Space middleware at this time; instead, we created simplified versions of the services specifically designed for the applications we would like to investigate. Functionalities such as message exchange between machines, file sharing, checking for application execution state and availability of computational resources, among others, had to be implemented. In addition to this project decision, instead of developing totally new applications we chose to use well established components. This approach, apart from drastically decreasing development time, also allowed us to integrate well known single-user [7] applications. Therefore, a great part of the ActivePresentation infrastructure is destined to provide integration and control mechanisms for existing applications and components. This approach, besides drastically reducing the development time of prototypes used to investigate new ideas, also allowed users to use applications with which they were already familiar. Hence, a great part of the ActivePresentation infrastructure’s purpose is to provide integration and control mechanisms for existing applications and software components. At times, the task of controlling different applications becomes quite complex because each application provides its own API and middleware technology such as Java, COM, .NET and CORBA. One possible approach for controlling such applications is to use interface standards for different APIs, providing adaptors that will be able to access different applications. Sometimes, this approach may restrict the available functionalities and increase development time due to the implementation of such adaptors. In this work we have tried an alternative approach in which we seek application control through their original API and middleware technology. To deal with the interoperability between different middleware, ActivePresentation uses LuaOrb [8, 9]. LuaOrb is a tool for the development of applications based on software-component standards such as Java, COM, .NET and CORBA, creating dynamic bridges across different componentware technologies. In addition, LuaOrb provides a simple and flexible interoperability mechanism, creating dynamic bridges between components of different technologies. The control of applications in a multifunctional workroom allows us to use them to orchestrate a distributed mul-

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Presentation Node Presentation Node Presentation Node Execution Supervisor

Application

Node Manager File Server

Controller Node Application Groups

Observer Execution Supervisor

Application

Figure 1. The ActivePresentation Infrastructure

timedia presentation or to use a group of different media in order to do synchronous collaborative work. Moreover, through the connection of different multifunctional rooms, this same infrastructure also enables us to coordinate applications in different locations. Because the user is allowed to control applications remotely, regardless of his location, he can take part in a collaborative work session.

3.1

General Architecture

The model presented in figure 1 shows the entities of the ActivePresentation infrastructure. The figure shows some Presentation Nodes, one Controller Node and the Node Manager. The Node Manager has Application Groups and a File Server; the Presentation Nodes have one Execution Supervisor and one Application each; the Controller Node has an Execution Supervisor, an Observer and an Application. Application The application seen in figure 1 is a software (either open source or not) that offers programmatic control of its execution. The automation interface, besides providing methods for executing specific application tasks, must allow them to be started and finished programmatically. Through the distribution of the automation interface, the application can be remotely controlled. Usually these remote method invocations demand low communication, offering an interesting solution for environments with 5

limited bandwidth capacity. Presentation Node The Presentation Node works as a wrapper for the application, allowing the application’s execution to be conducted and observed. This enclosure provides infrastructure functionalities to the Applications such as connectivity with the Node Manager, control of registered observers interested in the application’s notifications and access to data files. Because the Presentation Node is constantly connected to the Node Manager, even when no application is running it grants access to the device, thus enabling applications to be started and finished remotely and providing information about computational resources of the devices in which they are running. The process of including an application in the Presentation Node is very simple: a small layer must be built between the application and the node class in which methods to start and finish the application should be written. In addition, the application’s API must be distributed through the Node Manager. Because LuaOrb [8, 9] does type conversions, the user does not need to worry about converting data types between CORBA and the application’s API. Controller Node While the Presentation Node assumes a passive attitude towards other applications, the Controller Node acts actively controlling and observing them. By means of calls over a distributed automation interface, the Controller Node is able to control single applications or a group of them. By receiving events through the Observer service (which implements the well known Observer-Observable design pattern), the Controller Node can make decisions and adapt its execution accordingly. The Controller Node may be driven by different ways, such as a script, a user or an artificial intelligence program. The ActivePresentation infrastructure also allows more than one controller to be active at the same time, thus enabling a system to be operated through multiple interfaces and users. The separation between Presentation Node and Controller Node is for organizational purposes. Due to the many particular differences between each type of node, the different nomenclature helps to organize and structure the applications. Nevertheless, some implementations can mix functions of these two types of node. Node Manager The Node Manager centralizes information about Nodes and their running Applications. The separation between Node Manager and Nodes is similar to that of a client-server architecture, which could suggest a lack of scalability 6

in the solution. Nonetheless, this does not represent a problem due to the low communication traffic and the very little processing done in the Node Manager. In fact, the application built over the ActivePresentation infrastructure will not centralize processing functions in the Node Manager but rather will use the Presentation Nodes and the Controller Nodes. The Node Manager stores the following information about the Nodes: a name (usually the node’s machine name), a unique identifier, a remote reference of the node and a remote reference of the running application. Through this information, the Node Manager can answer questions such as which applications are in execution or which groups are active, among others. Besides, the Node Manager notifies observers about entering and exiting nodes and applications. Observer The Observer is responsible for receiving notifications sent by the applications running inside the Nodes or by the Node Manager itself. The notifications use a simple format that provides basic information about events; it is the responsibility of the receiver of such notifications to interpret them correctly. In the future, we expect to extend the notification messages so that it is possible to represent the application events exactly as they were generated. In order to do that we will probably use the XML standard. Application Groups To allow the simultaneous control of multiple applications, the ActivePresentation infrastructure offers a group mechanism. A group is capable of controlling multiple applications that share the same API. Groups are created and managed by a module called Application Group, which organizes them by name. Moreover, the Node Manager keeps the remote references to the applications organized in Application Groups, allowing generic group control for any kind of application. Notedly, all applications in a certain group must follow the same programming interface, semantic and should always be synchronized. Execution Supervisor The Execution Supervisor is responsible for initializing and terminating Applications and for registering and cleaning up references to it in the Node Manager. The Execution Supervisor ensures that at most one application is running inside the Presentation Node. When the Presentation Node is not running an application, the Execution Supervisor can be ordered to do so through its 7

constant connection to the Node Manager. In order to initiate and finish an application in a group, it may be necessary to use a data file. The Execution Supervisor is responsible for providing this file, requesting it from the Presentation Manager according to the group where the application belongs. File Server The File Server serves as a content provider, being able to manage multiple simultaneous connections. Typically, when executing a new application, the Execution Manager communicates with the Presentation Manager in order to obtain information about the file and where to find it; so, even though the File Server is presented here as part of the Node Manager, it can be developed to be separated from it. In the future, we expect to add the results obtained in Gaia’s [2] Context File System [10], which makes files appear or disappear from the virtual file system according to the current context of execution and provides streaming capabilities.

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Prototypes To verify the adequacy of ActivePresentation in the construction of collaborative work applications and distribu-

ted multimedia presentations, we developed some prototypes. We present in this section prototypes that integrate R and Windows Media Player , R two commercial applications that offer control through Microsoft PowerPoint

COM [11] automation. A simple abstraction of the COM interface of these applications allowed us to distribute them through CORBA [12]. In order to accomplish this we used the gluing language LuaOrb [8, 9], which facilitates interoperation between different middleware, converting data types and allowing the development of quick prototypes. In addition to those commercial applications, we integrated the 3D Navigator, an open-source tool built to allow the user to navigate through different three-dimensional models.

4.1

The First Prototype

R is very attractive as a presentation component due to the simplicity of its use but also Microsoft PowerPoint

because of its content-creation convenience. In addition, its user-friendly interface in the slide-show mode makes it an interesting tool for both cooperative work and distributed multimedia presentations.

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R presentation is seen on a cellular phone emulator Figure 2. A PowerPoint

Our main objective with this prototype was to check the infrastructure’s flexibility regarding application control. In order to do that we tested different types of group controllers, such as stand-alone applications, web pages, voice R recognizers, cellular phones and PowerPoint ’s own user interface. R Microsoft PowerPoint ’s automation interface allowed us to achieve good integration results. Functionalities

such as starting and finishing applications, file transfer and group control aided us in the construction of a system R instances worked in a synchronized manner across different for cooperative work in which multiple PowerPoint

machines. R application In a collaborative environment with debate and interaction, the distributed control of a PowerPoint

may be regulated by the following semantic: all slide change operations are sent to the group and the final slide is the result of the union of all actions. In the future, the ActivePresentation infrastructure will be altered to provide ways of organizing the controllers in a master-slave style, where only some controllers can make operations over the execution of an application. Using the development tool Brew [13] for CDMA cellular phones, we built a different viewer and controller for R application. Image 2 shows the Brew emulator, in which a small slide image of a real presentation the PowerPoint

is seen. The arrows also shown in the picture can be used to control the real presentation. Because Brew is a tool for mobile devices, it offers a reduced software infrastructure, allowing the communication between devices only through Sockets. In order to integrate the cellular device to the ActivePresentation infrastructure, we had to use a proxy which, through a simple communication protocol, integrated both systems. Figure 3 shows this system’s architecture. The Cellular Proxy was built as an application inside a Controller Node and receives commands from the cellular

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Presentation Node Application

Controller Node

Node Manager

Cellular Proxy

Application Groups

R control using Brew Figure 3. PowerPoint

phone requesting slide changes. Such commands are then forwarded to the Node Manager, which has control over R instances. If the user changes the PowerPoint R slide, the Controller Node receives a a group of PowerPoint

notification from the Presentation Node and can update the cellular phone with an image of the new slide.

4.2

The Second Prototype

R R was added as an audio Following PowerPoint ’s integration with ActivePresentation, Windows Media Player

and video reproduction tool. As before, we used the COM automation interface to control and observe events occurred during its execution. One of our goals in this prototype was to check the generality of the ActivePresentation infrastructure. Good R Our second objecresults were obtained when we implemented a distributed version of Windows Media Player .

tive was to combine both applications running in different machines in order to perform a distributed multimedia R presentation. To coordinate them, we built an application in a Controller Node to control a Microsoft PowerPoint

presentation synchronously with a video reproduction. We used the ASF video format [14], which allows time marks R which informs through the to be inserted in video files; these marks are recognized by Windows Media Player

automation interface when they are reached during a video reproduction. The notification of these events makes the R slide. Controller Node change the PowerPoint

4.3

The Third Prototype

Three-dimensional environments present in games, simulations and engineering projects are now part of the daily work in many companies. In our third prototype, we investigated the use of a visualization tool called 3D Navigator,

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R presentation Figure 4. Virtual control and visualization environment for a real PowerPoint

an application for three-dimensional navigation developed in our laboratory which provides facilities such as 3D model loading, smooth navigation control and interaction with objects. In this prototype we inserted the 3D Navigator into a Controller Node. Image 4 shows a screenshot of this 3D rendering program where a three-dimensional model of a computer is shown executing a fictitious instance of R The slide seen on the virtual computer’s screen is taken from a real PowerPoint R presentation which PowerPoint .

is taking place on a remote computer. The real presentation can be manipulated by clicking on the virtual arrows, which can be selected inside the 3D environment. Moreover, if a slide change happens in the real presentation, the image on the virtual computer is updated immediately. This prototype’s purpose was to explore the potential of the infrastructure, showing that different controllers can be created and used. In the future it can be used to remotely operate complex systems, thus allowing them to be controlled by a virtual interface with high resemblance to the real one.

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Related Works Currently, synchronous collaborative work between Active Spaces is done through systems that are naturally

distributed or systems that duplicate the execution of single-user [7] applications. Examples of naturally distributed systems are instant-message applications on the Internet and the World Wide Web. The ConferenceXP [15] project from Microsoft Research is an example of a naturally distributed system for collaborative work. This system offers, besides group-to-group videoconferencing, a selection of tools such as a PowerPoint Presentation application that generates slide images automatically, enabling a slide presentation to be

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viewed regardless of the person’s location, and Real-time Inking, which allows a group of separated people to draw on a virtual board. Systems that reproduce the execution of single-user applications can be divided in two categories: centralized systems, in which applications are executed in a single machine and their graphical output are transmitted to multiple devices, and replication systems, which actually run the applications in multiple machines in a synchronized way. Some commercial systems use the centralized architecture, such as NetMeeting and SunForum. This solution, although easier to implement, provides slow interaction with the user and, in case of disconnection with the server, invalidates the client immediately. The Access Grid [16, 17] project presents a system for group-to-group interaction which includes videoconfeR and Web Browsers. rencing and the use of replicated applications such as image viewers, video, PowerPoint

This project has a strong focus on the videoconference system and, as far as we know, does not have an elaborate infrastructure for the execution of group applications. The ABC Framework, described by J. Bardram [18], focuses on the construction of a framework for the use of replicated applications in a collaborative work session. The ABC Framework was also inspired in works that describe ubiquitous computing environments, such as Gaia and Aura [2, 3]. Moreover, the ABC Framework also researches the use of heterogeneous applications for the execution of the same task. We differentiate our project from this approach for we believe that the control of homogeneous applications has a more practical appeal due to its relative simplicity. We have analyzed some systems that execute multimedia presentations through application control, such as Online Presentations [19], Presentation Studio [20], Accordent’s PresenterOne [21] and StreamAuthor [22]. Each one of R Besides these, the HyperProp [23, these systems can perform audio and video synchronization with PowerPoint .

24] system allows control over different applications using the NCL [25, 26] file format to describe the spatial and temporal requirements of the presentation. Notably, these systems only work for execution in one machine.

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Conclusion and Future Works In this work we have presented ActivePresentation, a software infrastructure for application control in ubiquitous

computing environments. We observed that by means of the automation and distribution of the application’s programming interface, we could build synchronous collaborative applications using the available software technology. This approach is different from others that use only naturally distributed applications (for example, instant messaging systems), and we can integrate applications that are familiar to a greater community of users, such as Microsoft 12

R and Windows Media Player . R PowerPoint

We have discussed the functionalities necessary in ubiquitous computing environments, which we called Active Spaces, but our purpose was not to provide all the functionalities present in systems such as Gaia [2] or Aura [3]. Instead, we built an infrastructure to complement such systems, analyzing and implementing functionalities necessary for the accomplishment of our objectives. In section 4 we described prototypes built over the ActivePresentation infrastructure which confirm its efficiency. The flexibility of the infrastructure allowed us to use different controllers for both proprietary and open-source applications. We have shown that the remote access to applications allows us to determine relation and thus guide applications to compose a distributed multimedia presentation. In the future we plan to create an autonomous system that, guided by a multimedia document, can orchestrate a presentation. We intend to use the NCL [25, 26] description language for spatial and temporal synchronization, extending the language as necessary. We will deal with synchronization problems between machines possibly by adding new services to the ActivePresentation infrastructure. Moreover, we plan to integrate the ActivePresentation infrastructure with the Gaia Active Space system, as was already mentioned. We intend to use resource information services to dynamically adapt multimedia documents according to the different workrooms and to use the context file system to handle streaming while preparing a distributed multimedia presentation.

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Acknowledgments We would like to thank Luiz Gustavo Nogara and Reinaldo Mello for the implementation of LuaBrew and for the

R controller for cellular phones; Henrique Pinheiro for the research and conseffort in the creation of the PowerPoint

truction of some of the infrastructure’s modules; Vinicius Almendra for all the support in the use of LuaCom [27]; Frederico Abraham for his assistance in the construction of the 3D Navigator; and Carolina Alfaro for proofreading this document.

References [1] M. Weiser, “The computer for the 21st century,” Scientific American, vol. 256, no. 3, pp. 94–104, Sept. 1991. [2] M. Romn, C. Hess, R. Cerqueira, A. Ranganathan, R. H. Campbell, and K. Nahrstedt, “A middleware infrastructure for active spaces,” IEEE Pervasive Computing, vol. 1, no. 4, pp. 74–83, 2002. 13

[3] D. Garlan, D. P. Siewiorek, A. Smailagic, and P. Steenkiste, “Project aura: Toward distraction-free pervasive computing,” IEEE Pervasive Computing, April-June 2002, vol. 21, no. 2, pp. 22–31, 2002. [4] R. Ballagas, A. Szybalski, and A. Fox, “Patch panel: Enabling control-flow interoperability in ubicomp environments,” pp. 241–252, Mar. 2004. [5] R. Cerqueira, C. K. Hess, M. Romn, and R. H. Campbell, “Gaia: A development infrastructure for active spaces,” Workshop on Application Models and Programming Tools for Ubiquitous Computing, Sept. 2001. [6] P. Tandler, “The beach application model and software framework for synchronous collaboration in ubiquitous computing environments,” Journal of Systems and Software, vol. 69, no. 3, pp. 267–296, Jan. 2004. [7] D. Li and R. Li, “Transparent sharing and interoperation of heterogeneous single-user applications,” Computer supported cooperative work, pp. 246–255, 2002. [8] R. Cerqueira, C. Cassino, and R. Ierusalimschy, “Dynamic component gluing across different componentware systems,” International Symposium on Distributed Objects and Applications, 1999. [9] R. Cerqueira, LuaOrb, PUC-Rio, Rio de Janeiro, Brazil, May 2001, http://www.tecgraf.puc-rio.br/luaorb. [10] C. K. Hess and R. H. Campbell, “A context-aware data management system for ubiquitous computing applications,” International Conference of Distributed Computing Systems, May 2003. [11] D. Box, Essential COM.

Addison-Wesley, 1998.

[12] The Common Object Request Broker Architecture and Specification; Revision 2.2, OMG, Needham, MA, Feb. 1998, http://www.omg.org. [13] Brew Technology, Qualcomm, Jan. 2001, http://www.qualcomm.com/brew. [14] Advanced Systems Format (ASF) Specification, Microsoft Corporation, Redmond, WA, USA, Sept. 2003, http: //www.microsoft.com/windows/windowsmedia/format/asfspec.aspx. [15] Conference XP, Microsoft Research, Redmond, WA, USA, 2002, http://www.conferencexp.net/. [16] L. Childers, T. Disz, R. Olson, M. E. Papka, R. Stevens, and T. Udeshi, Access Grid: Immersive Groupto-Group Collaborative Visualization, Argonne National Laboratory and University of Chicago, 2000, http: //www-unix.mcs.anl.gov/fl/publications/childers00.pdf. 14

[17] J. T. von Hoffman and V. Venkataraman, User’s Guide to Shared Applications for AG Toolkit, Boston University, May 2004. [18] J. E. Bardram, “Supporting mobility and collaboration in ubiquitous computing,” Aarhus, Denmark, Tech. Rep., 2003. [19] J. Hunter and S. Little, Building and Indexing a Distributed Multimedia Presentation Archive using SMIL, University of Queensland, Australia, Mar. 2001, http://archive.dstc.edu.au/RDU/staff/jane-hunter/ECDL01/ ECDL01.html. [20] Presentation Studio, WebEx, 2004, http://www.presenter.com/. [21] Accordent’s PresenterOne, Real Networks, 2004, http://www.realnetworks.com/products/presenterone/. [22] StreamAuthor, CyberLink Corp, 2004, http://www.gocyberlink.com/english/products/product main.jsp? ProdId=32. [23] L. F. G. Soares, R. F. Rodrigues, and D. C. M. Saade, “Modeling, authoring and formatting hypermedia documents in the hyperprop system,” ACM Multimedia Systems Journal - ACM, pp. 118–134, Mar. 2000. [24] R. F. Rodrigues, L. M. Rodrigues, and L. F. G. Soares, “A framework for event-driven hypermedia presentation systems,” VIII Multimedia Modeling Conference - MMM2001, pp. 169–185, Nov. 2001. [25] M. J. Antonacci, “Ncl: Declarative language for hypermedia document authoring with spatial and temporal synchronization,” Master’s thesis, PUC-Rio, Rio de Janeiro, Brazil, Apr. 2000, portuguese only. [26] D. C. M. Saade, “Relations in hypermedia authoring languages: Improving reuse and expressiveness,” Ph.D. dissertation, PUC-Rio, Rio de Janeiro, Brazil, Mar. 2003. [27] R. Cerqueira and V. Almendra, LuaCom, PUC-Rio, Rio de Janeiro, Brazil, 2004, http://www.tecgraf.puc-rio. br/∼rcerq/luacom/.

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