A. Y. Al-Zoubi and Akram Alkouz
Princess Sumaya University for Technology, Al-Jubaiha 11941, Amman, Jordan
Keywords: eLearning, Learning objects, Synchronized Multimedia Integration Language, on-the-fly SMIL generator.
Abstract: Learning objects are usually targets to transfer from one repository to another or subject to modifications
due to the unavailability of the server running the repository. Synchronized Multimedia Integration
Language (SMIL) has recently become increasingly important in eLearning environments to integrate
learning objects into a synchronized complex multimedia web presentation. However, this standard
specification lacks the ability to provide alternative links in the case of repository unavailability and may
occasionally lead to broken links. An outline of various aspects of the design and implementation of web
services based on-the-fly SMIL generator architecture (WSOSGA) is presented in this paper. WSOSGA
consists of three tiers which cooperate together in a simple way to search for multimedia learning objects
both locally and in the internet, rank them based on learning objects (LO) author considerations, generate
and publish the corresponding SMIL document and its XML profile. The latter will be used by the web
services tiers on the target web server to generate SMIL documents on-the-fly. The major advantage of
WSOSGA is thus achieved to give SMIL presentations high availability in eLearning instructional content.
Technology enhanced learning has become one of
the most important applications of the multimedia
information network (Meleis, 1996). Learning
experiences by electronic technology are expanding
rapidly since the World Wide Web (WWW)
technologies have been adapted in the eLearning
process. Learning Objects (LO), which may form
digital or non-digital entities, are the base
components of eLearning systems. They can be
used, reused or referenced during technology
supported learning. However, integrating
heterogeneous LOs such as video, audio, text, and
pictures into a standard format is a considerable
challenge. It requires the organization of LOs in both
spatial and temporal dimensions and subsequently
supporting a hypertext structure to provide
interactivity. Several solutions, including MHEG
(Prie, 1993) and HyTime (ISO/IEC et al., 1997),
have been proposed to resolve this challenge, but the
Synchronized Multimedia Integration Language
(SMIL) remains the most suitable standard for the
creation and management of multimedia
presentations (W3C Recommendation).
Link management has been examined thoroughly
through display of links to a particular object,
detection of dangling links, and display of links
relevant for selected structure or channel view items
(Rutledge et al., 1999). Existing tools for writing
SMIL documents such as Smily, provide a powerful
and controllable authoring environment close to the
well-known WYSIWYG paradigm used by usual
word processors (Kodali et al., 2004) A modification
to SMIL in order to enhance its performance lead to
the new unbreakable synchronization constructs
SMIL version (uSMIL), where parallel and
sequential constructs require that all their
components be played out, otherwise or none is
played. Nonetheless, no solutions were provided to
dynamically substitute the broken links (Muriel et
al., 1999)
In addition, SMIL provides a set of XML tags for
building interactive multimedia presentation that
may include animations and hyperlinks. SMIL is not
an attempt to specify the data formats of time-based
media; but rather it provides a way for authors to
Y. Al-Zoubi A. and Alkouz A. (2007).
In Proceedings of the Third International Conference on Web Information Systems and Technologies - Society, e-Business and e-Government /
e-Learning, pages 487-490
DOI: 10.5220/0001266804870490
schedule operating time-based media within
documents. The multimedia LOs are usually
referenced by simple URL hypertext links and stored
on distributed repositories. These repositories may
not be available at all times due to hardware or
software malfunctioning, which subsequently lead to
broken links.
Furthermore, the newer version 2.0 of SMIL
contains modules referred to as structure, layout,
media, content control, linking, timing and
synchronization, animation, time manipulations,
transition effects and meta information.
Unfortunately, none of these modules deal with the
problem of repository unavailability (Sampaio et al,
In this paper, the design architecture and
implementation of web services based on-the-fly
SMIL generator architecture (WSOSGA) is
presented. The proposed WSOSGA architecture
consists of three tiers which are synchronized to
search for multimedia LOs both locally and in the
internet. The new design is able to rank, generate
and publish the corresponding SMIL document and
its associated XML profile. This gives the web
services tiers on the target web server the ability to
generate SMIL documents on-the-fly. The major
advantage of WSOSGA is thus achieved to give
SMIL eLearning instructional content presentations
high availability.
The proposed new architecture is presented in Figure
(1). The architecture consists of three tiers. The first
tier is for the client which includes the SMIL editor
that is used to compose SMIL documents. This tier
can search for LOs in distributed repositories. The
SMIL editor will also rank LOs of the same category
and generate a corresponding XML profile which
includes the alternative links that will be used in
case of repository unavailability depending on the
ranks selected. Tier two is the Master Web Service
(MWS) which is responsible for the on-the-fly
generation of SMIL documents based on XML
profile. The last tier is Image-Video-Audio-Text
(IVAT), which is a set of dynamically multithreaded
web services responsible for the process of checking
the availability of multimedia objects on the
specified repositories.
From an architectural viewpoint, WSOSGA has
two different use cases, one from the authors of
SMIL documents viewpoint and the other from the
users of SMIL documents viewpoint. The client tier
handles the processes of the author’s use case, while
the middle and backend tiers handle the processes of
user’s case.
2.1 Client Tier
The client tier consists of the SMIL user interface
editor which is utilized to compose documents based
on SMIL 2.1 specifications (W3C
Recommendation). These specifications divide the
document area to several regions using the <region>
tag (Synchronized Multimedia on the web). Each
region is dedicated to one type of the multimedia
objects, mainly image, video, audio, and text. The
SMIL editor acts as a web services client with search
capabilities through local and distributed repositories
for LOs that match the user criteria.
Figure 1: WSOSGA architecture and SMIL document
author’s use case.
A list of retrieved LOs will be shown to the user
to rank based on specific considerations. Rank
weights will be used as the base to substitute the
alternative LOs links in the case of repository
unavailability. The SMIL editor will generate an
HTML file and a corresponding XML profile for
each document to be published on the web server.
The HTML file will have a server side call for the
MWS in the middle tier as illustrated in Figure (1).
The XML profile will thus be used by the MWS as
an entry parameter to generate the SMIL document
2.2 Middle Tier
Middle tier contains the MWS, which is hosted on
the web server and can act as a web service client.
While users browsing the multimedia presentation, a
HTTP request for the corresponding HTML file will
be generated. The HTML will initialize a SOAP,, server side
call for the MWS with the corresponding XML
WEBIST 2007 - International Conference on Web Information Systems and Technologies
profile as a parameter. Once the MWS is invoked, it
will parse the XML profile and starts generating the
SMIL document. The MWS will make a
synchronous SOAP call for the corresponding IVAT
web service in the backend tier throughout the
generation process if a clear URL reference is
encountered, as in shown in Figure (2). The list of
links for LO that was ranked by SMIL document
author will be passed as a parameter for the IVAT
web services: I, V, A, and T corresponding to the
object type: Image, Video, Audio, and Text. The
MWS will generate SOAP synchronous calls to the
corresponding IVAT web service as the number of
alternative links to each individual LO in XML
profile; each link will be processed in a separate
thread of the corresponding IVAT web service.
Figure 2: WSOSGA SMIL document user’s use case.
2.3 Back-end Tier
Back-end tier consist of the IVAT web services,
which are a dynamically multithreaded web services.
IVAT web services are used to check the availability
of the corresponding LOs. Once the IVAT web
service received the SOAP asynchronous call from
the MWS with the list of links to the corresponding
LO as a parameter, a new thread will be invoked to
process each link. The thread will check the
availability of the LO by trying to retrieves it. The
first thread returns with confirmation will kill the
rest of the threads to maintain reasonable server
performance and returns a confirmation message to
the MWS. The confirmation message includes the
link to the highly available LO. In this way, the
MWS will generate the SMIL document on-the-fly
with a committed available link to LOs, and return
back to the user. Thus, the three tiers are cooperating
to achieve the on-the-fly generation of highly
available SMIL presentations while maintaining
adequate system performance.
Microsoft.Net 2 framework was chosen as a
platform to implement the proposed WSOSGA
system due to its simplicity, availability and low
cost, in addition to its maturity and wide spread
popularity. The SMIL editor was however
implemented as an ASP.Net web application while
the Internet Information Server was used to host the
web application because of its ease of web-service
deployment and its main characteristics as being
user friendly. The web search algorithm to retrieve
LOs from local and distributed repositories was an
important parameter of proposed system. It was
consequently decided to utilize the TREC Ad-Hoc
Algorithm,, in
the WSOSGA as means of Learning Objects
retrieval because link-based ranking schemes
outperforms keyword-based algorithm by a large
margin. Such queries are quite prevalent in web
search. This leads to an efficient ranking of LOs in
the SMIL editor. The SMIL editor has been tested in
typical network environment. Its search capabilities
were compared to existing SMIL editors such as
GriNS Pro Edition for SMIL 2.0,
ex.html and PresenterOne
/index.html. The results show that this new SMIL
editor outperforms traditional SMIL editors in a
number of aspects, mainly speed and query quality.
Integrating the proposed SMIL editor with
commonly used eLearning platforms such as
WebCT, Moodle and CourseWork would be a
valuable element in enabling authors to rank their
existing LO efficiently. This would also be an
important step towards the standardization of the
proposed WSOSGA system.
Master Web Service, which is the core of middle
tier, was implemented based on standard web
services technology in Dot.Net framework and
hosted on the web server where HTML and XML
profiles are hosted. The MWS here acts
simultaneously as client and server by responding to
SOAP requests form ASP.Net client. At the mean
time, it implements the proxy file of the IVAT web
services. This scheme reduces the processing
overhead of mapping and results in increasing the
speed of individual IVAT web services calling. The
amount of overheads generated is minimized
compared to the standard method of hyper linking
LOs in which the clear URL appears in HTML file
format. The remaining overheads that have been
created as a result of both SOAP calls to MWS and
IVAT web services should be measured to estimate
the processing overhead and network traffic.
Measurement, which has been performed using
Ipswitch WhatsUp Professional Premium tools,
shows a significant increase in network traffic. In
addition, the level of processing overhead caused by
parsing XML profile was found acceptable because
of the implementation of multithreaded MWS.
The backend tier was hosted on a separate web
server, in order to maintain the system at a normal
performance level. Subsequently, asynchronous
SOAP calls to IVAT web services were used and
each link availability was checked in a separated
thread. This resulted in a highly efficient system
performance and increased LOs availability. A
further advantage of this scheme to the client is the
transparency achieved by hosting middle tier and
backend tier servers in the same LAN where the
network traffic takes place.
The overall system performance may be further
improved by incorporating means such as caching
mechanisms. The high availability of LOs it offers
remains its major advantage which makes the
proposed system an efficient architecture for
implementation in standard eLearning platforms,
particularly from authors’ perspective. Its integration
in such platforms should seriously be considered.
A new system of web services based on on-the-fly
SMIL generator architecture was proposed to
provide high availability of learning objects for
eLearning presentations. The system consists of
three tiers designed to search for multimedia
learning objects, publish and generate the SMIL
documents on-the-fly. The system may be
considered as an efficient method for
implementation in standard eLearning platforms. Its
speed, which is degraded by its inherent on-the-fly
mechanism, may however be improved by
incorporating means, such as caching mechanisms,
in order to make it a competitive candidate for
integration in popular eLearning platforms such as
WebCT, Moodle and CourseWork
Kodali, N., Farkas C., and Wijesekera D., “Creating Non-
Decomposable stream Bundles in Multimedia Web
Services using uSMIL”, Proceedings of the 2004
workshop on Secure web service, pp. 67-76 , ACM
Press, Fairfax, Virginia, 2004.
Muriel J., Laurent T., Lionel V., “SMILY, a SMIL
authoring environment”, Proceedings of the seventh
ACM international conference on Multimedia (Part2),
pp. 198 , ACM Press, Orlando, Florida, United States ,
Meleis, H., “Toward the Information Network”, IEEE
Computer Magazine. Vol. 29 (10): pp 59-67, 1996.
Rutledge L., Hardman L., Dick C. and Bulterman A,
“GRiNS: a graphical interface for SMIL”, Proceedings
of the seventh ACM international conference on
Multimedia (Part 2), pp. 200, ACM Press, Orlando,
Florida, United States, 1999.
Prie R., “MHEG: An Introduction to the Future of
International Standard for Hypermedia Object
Interchange”, Proceedings of the First ACM
Conference on Multimedia, pp. 121-128, ACM Press,
Anahiem California, August 1993.
Sampaio P.N.M, Lohr C., Courtiat J.P, “An Integrated
Environment for the Presentation of Consistent SMIL
2.0 Documents”, Proceedings of the 2001 ACM
Symposium on Document engineering, pp.115-124,
ACM Press, Atlanta, Georgia, USA, November 2001.
ISO/IEC JTC1/SC18/WG8 N1920, Information
Technology: Hypermedia/Time-based Structuring
Language (HyTime), Second edition, ISO/IEC, 1997,
W3C Recommendation, “Synchronized Multimedia
Integration Language (SMIL) 2.1 Specification”,
“Synchronized Multimedia on the web”,
“Web Services Addressing 1.0, SOAP Binding”,
“A Case Study in Web Search using TREC Algorithms”,
“GriNS Pro Edition for SMIL 2.0“,
WEBIST 2007 - International Conference on Web Information Systems and Technologies