NEW WEB SERVICES BASED ON-THE-FLY SMIL GENERATOR

ARCHITECTURE FOR HIGHLY AVAILABLE ELEARNING

PRESENTATION

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.

1 INTRODUCTION

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

487

Y. Al-Zoubi A. and Alkouz A. (2007).

NEW WEB SERVICES BASED ON-THE-FLY SMIL GENERATOR ARCHITECTURE FOR HIGHLY AVAILABLE ELEARNING PRESENTATION.

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

 SciTePress

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,

2001).

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.

2 SYSTEM ARCHITECTURE

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

on-the-fly.

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,

http://www.w3.org/TR/ws-addr-soap, server side

call for the MWS with the corresponding XML

WEBIST 2007 - International Conference on Web Information Systems and Technologies

488

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.

3 RESULTS AND DISCUSSION

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, http://www.w3.org/TR/ws-addr-soap, 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

Fluition, http://www10.org/cdrom/papers/317/,

GriNS Pro Edition for SMIL 2.0,

http://www.realnetworks.com/products/editorpro/ind

ex.html and PresenterOne

http://www.realnetworks.com/products/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

NEW WEB SERVICES BASED ON-THE-FLY SMIL GENERATOR ARCHITECTURE FOR HIGHLY AVAILABLE

ELEARNING PRESENTATION

489

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.

4 CONCLUSIONS

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

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