[PDF]Provisioning a Restful Pedagogical Service in the Cloud

Provisioning a Restful Pedagogical Service

in the Cloud



Shueh-Cheng Hu #1 , I-Ching Chen #2 , Yaw-Ling Lin #3

m Dept. of Computer Sci. & Communication Engineering

Providence University, Taichung, Taiwan, ROC

'schuOpu . edu . tw

#2 Dept. of Information Management

Chung Chou University of Science and Technology, Changhua, Taiwan, ROC

2 j ineOdragon . ccut . edu . tw

#3 Dept. of Computer Science & Information Engineering

Providence University, Taichung, Taiwan, ROC

yllinOpu . edu . tw



Abstract — Online education and training play critical roles in the
age of Internet. For easy sharing and reusing pedagogical
resources that are high-priced to develop, there are standards for
encoding instructional contents and regulating their
presentational formats. However, because access interfaces and
message packing schemes of most e-learning resources are still
proprietary, the offered contents are available to privileged users
only and thus are difficult to utilize and circulate. SOAP-based
Web services to some extent solve the openness issue by enforcing
contents and their packing schemes conform to pre-defined
formats. To enrich online pedagogical resources and facilitate
sharing them among educators and learners, it is of great
importance to build them in not only open, but also efficient and
easy-accessible way. This article proposes an approach for
provisioning pedagogical resources in the cloud based upon the
representational state transfer architectural (REST) style. The
anticipation is that the constructed services enable instructors
and students to easily use a variety of devices to access
pedagogical resources under diverse learning circumstances,
which is realization of the so-called ubiquitous learning.

Keywords — e-learning; pedagogical resources; cloud computing;
SaaS; Restful Web services

I. Introduction
Many organizations have embraced e-
learning technologies and programs to train
employees or serve their customers. Comparing
with conventional classroom training, the merits
brought by e-learning are the flexible time and
location for conducting learning activities, as well
as adaptive instruction materials. To build qualified
e-learning environments, much effort are necessary
to maintain online instructional materials up-to-
dated and satisfactory. Another issue is to meet
diverse education needs, instructional packages
usually need to be delivered in different contexts
and at different level of difficulty. To manage and
deliver online pedagogical resources in a flexible
and efficient way, this article takes online question
bank as an example to clarify the corresponding



concepts and illustrate the design rationales of the
proposed solution.

Online question bank systems, or known as
e-assessment modules in the e-learning context,
acquire and store contents comprising test questions
and the corresponding answers in advance, and then
deliver requested contents on demand. Despite there
are some concern regarding the effectiveness of
their usage, they do have advantages such as
dynamic composition of test, promptly providing
questions and instantly receiving feedback so
instructors are able to identify learners' strength and
weakness [1] whenever they intend to do so.

To enrich banks' contents, it is necessary to
harness collective intelligence and instructional
experience from educators. Researchers have been
trying to find solutions to facilitate the
compatibility among different question banks [2].
The most well-known concrete result is the question
& test interoperability (QTI) specification [3],
which is currently regulated and maintained by the
IMS Global Learning Consortium. However, the
QTI only enforces the compatibility among the
contents from different question banks by applying
a common representational schema in XML.
Beyond the contents' compatibility issue, an open
and easy-to-access interface to online question
banks is vital to facilitate the utilizing, reusing, and
sharing of valuable contents from educators with
diverse perspectives and instructional experiences.

Among many advantages of service-based
pedagogical resources [4], the most attractive one to



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both content consumers and providers is the open
access method that are based on existing
standardized techniques including HTTP, XML,
and Simple Object Access Protocol (SOAP), etc.
Besides being able to couple distributed and
heterogeneous software applications, the
standardization and the derived openness and
interoperability ease the access to service-based
resources and the composition of them. The
traditional SOAP-based Web applications apply the
SOAP to encapsulate the messages being
transferred between service consumers and
providers. Consequently, the composing and
parsing of SOAP messages result in significant
processing overhead not only on server sides, but
also on client sides, which usually own inferior
processing power than computers with conventional
form factors. The overhead not only affects the
performance adversely, also indirectly restrains
users' selectivity of devices that they can use to
efficiently consume available online services [5].

To resolve the aforementioned issues, the
representational state transfer (REST) architectural
style [6] offers a promising approach. Accordingly,
this article proposed an online question bank that is
designed with restful Web service and the
associated techniques. The proposed architecture
embodies merits including lightweight, pervasive
access, scalability, and flexibility.

The remaining parts of this paper are
organized as follows: Section II briefs related
techniques and the prior works. Section III
discusses the design rationales of the proposed
architecture. Concluding remarks and future works
are outlined in the last section.

II. Related Techniques and prior works

The cloud learning or service-oriented
learning approach fundamentally changes the way
of provisioning pedagogical resources. Basically,
pedagogical resources are prepared in advance and
accessible through Web service providers during
instructional process, as Fig. 1 illustrates. In other
words, all pedagogical resources in the cloud could
be wrapped and offered in the form of service, and
then, learning management systems can



dynamically request required services on demand
and on behalf of learners.

Cloud h aiding pedagogical resources




Fig. 1 The provision of learning materials in cloud learning environments

In summary, the service-oriented approach
for conducting Web-based instructional processes
will bring a number of advantages over the current
approach. Besides the general ones such as flexible
and evolvable structure, distributed and cross-
platform operational environment, those in the
context of e-learning include first, the improved
recentness and consistency of instructional
materials. Because instructional resources access
through dynamic linkage ensures that learners can
retrieve the latest updated instructional contents
from providers on demand. On the other side, there
will be reduced inconsistency among different
courses that share the same resource, that is because
every user acquires the contents dynamically,
instead of duplicating and embedding individual
copies to different course packages separately.
Second, an unleashed, or at least more extensible,
scope of reachable pedagogical resources is
possible. This aspect allows learners to experience
best available learning contents, no matter where
the contents are located. In other words, all
pedagogical resources through accessible services
rather than only those pre-packed in a collection
could serve learner's needs upon request. This
definitely will enrich the learning experiences of all
types of learners. Third, from the perspective of e-
learning contents providers, the service-oriented
approach of delivering instructional contents
enables the centralized control scheme over



37



learning resources. In other words, a centralized-
paradigm for managing learning resources allows
the providers of e-learning contents to conduct
access control, right management, and maintenance
works more efficiently and effectively, comparing
with the monolithic approach.

When Web service techniques were applied
in the provision of e-learning resources, its
platform-neutrality characteristic means no matter
which implementation techniques and operating
platforms were chose, once an instructional
resource was developed or just wrapped as a service,
all clients on the Internet can send compliant
request to access it. Obviously, that will leverage
the reusability and sharing of learning objects and
instructional processes beyond the current level,
which is conducted by the SCORM-compliant e-
learning products.

Basically, there are two kinds of Web
service enabling technologies: SOAP (Simple
Object Access Protocol) based and REST
(REpresentational State Transfer) styled. Due to the
overhead of volume message processing, the
SOAP-based Web services became bulky to sites
with intensive traffic. To address the issue, the
REST-styled service presented by Roy Fielding in
his dissertation [6] looks a promising approach for
architecting various Web services that need to serve
vast amount of user requests.

The Restful Web applications [7] emerged
as an lightweight alternative for realizing the
concept of software as a service (SaaS) [8, 9],
which is one of the major service delivery models
in cloud computing [10] environment, the other two
service models are infrastructure as a service (IaaS)
and platform as a service (PaaS). In a SaaS model,
functionalities are delivered to users through the
Internet; users do not need executable files and data,
instead, they are hosted in the cloud. Basically,
users can consume SaaS via a Web client software
(browser) that might run on diverse form factors
such as smart phones, thin clients, tablet PCs,
desktops, and so on. Besides offering a fairer
pricing scheme that charge users based on real
usage, the SaaS model accelerated functions and



data delivery, this feature is very critical to modern
learning platforms where people keep up with new
knowledge and skills for better competitiveness.

In a restful Web application, everything that
could be accessed or operated are treated as
resources. The resources must be identifiable via an
uniform naming scheme, and the uniform resource
identifier (URI) is practically used in all restful
Web applications. In contrast with its heavyweight
counterpart: the SOAP-based Web service, the
restful Web service associates standard HTTP
methods with operations that intended to be
performed on resources. In general, the four basic
HTTP methods: PUT, GET, POST, and DELETE
have been used to symbolize the create, retrieve,
update, and delete operations on resources,
respectively. For example, to identify a pedagogical
resource comprising a bank of questions on a
specific subject: Java programming, the provider
can use the URI like

http://www.onlineqb.org/banks/java/; to retrieve all
question items from that resource, a HTTP GET
request could be sent to the URI; identifier of the
target resource.

Due to the open and uniform identifying
scheme and access (operation) interface, the restful
approach significantly reduces the complexity that
are caused by the required processing of SOAP-
based messages; either message composition or
decomposition. Consequently, message recipients
can receive and then directly interpret (map) the
request sent by users. Such reduction offers users
and bystanders a lightweight option for utilizing
Web services in the cloud. Moreover, the plain
HTTP-based access interface facilitates the
integration of popular and lightweight techniques
such as asynchronous JavaScript and XML (AJAX)
into client side of restful Web applications, which
further enables more service consumers using
devices with various form factors to access online
pedagogical resources ubiquitously.

Not surprisingly, the aforementioned
strengths motivated flagship online enterprises
including Yahoo, Facebook, and Google that must
handle millions of user requests daily, to
aggressively adopt the restful approach for



38



developing their Web applications and publish the
corresponding APIs with an eye to the performance
and pervasiveness. Besides online enterprises,
research organizations such as the Lawrence
Berkeley National Laboratory also developed a
restful API for scientists, thus they can remotely
access an array of high performance computing
(HPC) resources that were deployed within the
laboratory via light-weight mobile devices with
Web browser [11]. Besides, an early feasibility
prototype using restful Web service in
telecommunication industry also indicated that the
REST architectural style is also suitable for
bridging services across technologies and
application domains [12]. In summary, the restful
style have being applied to develop Web
applications with diverse purposes [13-16].

III. Design rationales of the proposed architecture

The proposed architecture of online question
bank consists of major components as shown in Fig.
2. Fundamentally, the architecture is similar to the
multi-tier structure of typical Web applications. The
noticeable features include the usage of the restlet
[17], an API and a reference implementation of
Java-based restful Web service interface (JAX-RS
1.0). The restlet framework aims to simplify and
speed up the development of restful Web
applications with Java technologies. The
implementation of this work chose restlet Java EE
edition, which allows our restful Web services run
on regular JVMs or in servlet containers. The
Apache Tomcat was used as a servelt container to
host resources that were developed within restlet
framework.




% 8-



I



Dala rtiiw
-« ►






■ s. a



Fig. 2 The architecture of the proposed pedagogical resources provisioning

Regarding the response messages, typical
restful applications allows that resources have



different representation formats, e.g. plain text,
XML, and JavaScript Object Notation (JSON) [18],
etc. The client usually can ask for specific
representation via the content negotiation protocol.
In the proposed design, JSON is chosen due to its
native compatibility with JavaScript-enabled Web
clients. On the client side, any devices running
browsers that can handle a particular AJAX object:
XMLHttp Request can be served as a platform for
using and administering available restful resources.

Another feature is that the uniform interface
for accessing all resources in this question bank,
which include sub-banks with items in particular
subject, question items, and the corresponding
answer items that are persisted in a relational
database. The design of the interface for accessing
this question bank complied with the following
constraints: first, all types of resources in the bank
will be organized in hierarchical style, e.g., the
bank consists several of sub-banks that in turn
comprising questions associated with a specific
subject domain, and one question may contain a
number of valid answers. Second, identifiers of all
resources follow a common URI pattern, and thus
could be represented hierarchically. For example, to
identify a particular (say, the 100th one) question
item in a sub-bank focusing on specific subject
domain: Java programming, we can use
http://www.onlineqb.org/banks/java/100,
correspondingly, the 2nd valid answer to this
question item could be identified via
http://www.onlineqb.Org/banks/java/100/2. Third,
the four basic HTTP methods: POST, GET, PUT,
and DELETE are uniformly used to map the CRUD
(Create, Read, Update, Delete) operations on a
resource, respectively. Accordingly, to create a new
instance for the 2nd valid answer of the 100th
question item, a POST request including the HTTP
verb and the answer contents would be sent to
http://www.onlineqb.Org/banks/java/100/2.

In general, the APIs for accessing question
items about a particular subject such as Java
programming, could be formatted as TABLE I
shows. Overall speaking, all the features and
constraints mentioned above will make the online



39



question bank lightweight (high performance), easy
to use (pervasiveness), and scalable (elasticity).



TABLE I

API DESCRIPTIONS OF RESTFUL RESOURCES



API function


HTTP
method


URL path


Retrieve all
items


GET


/banks/java


Create a new
item


POST


/banks/java


Retrieve details
of a particular
question item


GET


/banks/java/[item_id]


Change details
of a particular
question item


PUT


/banks/java/[item_id]


Delete a
particular
question item


DELETE


/banks/j ava/[item_id]



IV. Conclusions

Cloud computing offers people a new
approach to utilize computing resources, either
hardware or software. Comparing with the present
usage of computing resources, the new approach is
more elastic, fairer in terms of pricing scheme, and
energy-efficient.

The "software as a service" concept in the
cloud computing field, can realize the pay-per-use
model, has being substantially reshaped the way
that people develop, utilize and maintain software.
Basically, there are two techniques for realizing the
SaaS concept: SOAP and REST. Comparing with
its SOAP-based counterpart, restful Web service is
relatively favorable in terms of implementation
complexity and message processing overhead. This
simplicity makes restful Web applications not only
lightweight, but also easier to use from the
perspective of patrons who need to use various
devices to access resources in the cloud.

This article proposed an restful approach for
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