GETTING SERIOUS ABOUT PROVIDING MOBILE WEB

SERVICE

Marc Jansen

Computer Science Institute, University of Applied Sciences Ruhr West, Tannenstr. 43, 46240 Bottrop, Germany

Keywords: Mobile Devices, Web Services, Mobile Web Service Provider.

Abstract: The role of mobile devices as Web Service consumers is widely accepted and a large number of mobile

applications already consumes Web Services in order to fullfill their task. Nevertheless, the growing number

of powerful mobile devices, e.g. mobile phones, tablets, … even raise the question whether these devices

can not only be used as Web Service consumers but at the same time also as Web Service providers.

Therefore, this paper presents an approach that allows to deploy Web Services on mobile devices by the

usage of the well-known protocols and standards, e.g. SOAP/REST and WSDL.

1 INTRODUCTION

In recent years the number of reasonably powerful

mobile devices has increased a lot. According to

(IDC, 2011) the number of smartphones worldwide

calculates to about 300 million units.

On the other hand, these huge number of

smartphones does also provide a large number of

heterogeneous devices, with respect to the operating

system that smartphones are currently using.

According to (Tudor, Pettey, 2010), there were at

least five different operating systems for

smartphones available on the market in 2010.

Therefore, a platform independent mechanism

for the communication with services provided by

smartphones seems to be necessary in order not to

re-implement each service for each of the mentioned

operating systems.

Here, nowadays usually Web Services are used

in order to provide a standardized and widely used

methodology that is capable of achieving a platform

independent way to provide services. Unfortunately,

in contrast to consuming Web Services on mobile

devices, providing Web Services on mobile devices

is not yet standardized due to several problems that

occur if a service runs on a mobile device.

This paper presents the description of a

framework that allows to provide Web Services on

mobile devices.

2 RELATED WORK

Probably the first idea of providing Web Service on

mobile devices was presented by IBM (McFaddin,

Narayanaswami, Raghunath 2003). This work

presents a solution for a specific scenario were Web

Service were hosted on mobile devices. More

general approaches for providing Web Services on

mobile devices are e.g. presented in (Srirama, Jarke,

Prinz, 2006) and (AlShahwan , Moessner, 2010).

In (Li, Chou, 2010) another approach focussing

on the optimization of the HTTP protocol for mobile

Web Service provisioning is presented.

Unfortunately, none of the formerly mentioned

approaches manages to overcome certain limitations

of mobile devices, as described in the next chapter.

The major difference between the former

research and the approach presented in this paper is

that, to the best of our knowledge, the former

research focuses very much on bringing Web

Services to mobile devices by implementing server

side functionality to the mobile device in question.

The approach presented in this paper follows a

different approach: from a technical and

communication point of view, the mobile Web

Service provider communicates as a Web Service

client with a dynamically generated Web Service

proxy.

This approach provides the advantage to

overcome certain problems with mobile Web

Services as described in the next chapter.

Furthermore, this approach does not rely on an

efficient server side implementation of Web

Services on the mobile device, which allows to

implement a very lightweight substitution to a usual

application server were a usual Web Service is

268

Jansen M..

GETTING SERIOUS ABOUT PROVIDING MOBILE WEB SERVICE.

DOI: 10.5220/0003935402680271

In Proceedings of the 8th International Conference on Web Information Systems and Technologies (WEBIST-2012), pages 268-271

ISBN: 978-989-8565-08-2

 2012 SCITEPRESS (Science and Technology Publications, Lda.)

running in.

Since there is nothing like a free lunch, this

approach also provides some drawbacks, e.g. the

presented approach implements a polling mechanism

that permanently polls for new service requests.

Therefore, this approach provides an overhead with

respect to the network communication and the

computational power of the mobile device. At least

the part with the computational overhead can

dramatically be reduced by adjusting the priority of

the polling mechanism, according to the priority of

the provided Web Service.

Another drawback of the presented approach is

that it relies on a publicly available proxy

infrastructure for the part of the framework that

dynamically generates the Web Service proxies.

This drawback might be overcome, e.g. if mobile

telecommunication companies provide this kind of

infrastructure centrally.

In contrast to the before mentioned approaches,

the approach presented in this paper differs with

respect to one major aspect: from a network

technical point of view, there is no server instance

installed on the mobile device. Therefore, a certain

Web Service client does not call the Web Service on

the mobile device directly but calls a centrally

deployed proxy. The Web Service running on the

mobile device polls in regular intervals for any new

message requests of interest. The exact sequence of

the different messages and events are described in

more detail in section 4.1. Since especially polling

mechanisms also provide a certain drawback, one of

the major questions concerning the presented

approach is the question of benefits and drawbacks

of the polling mechanism and in particular whether

the benefits justify the drawbacks.

As already mentioned before, one of the major

problems by dealing with Web Services on mobile

devices is the fact that mobile devices usually switch

their networks pretty often. Therefore, the Web

Service running on a mobile device is usually not

available under a fixed address, which leads to a

number of problems for the consumer of a mobile

Web Service. Besides the usual network switch, also

the fact that mobile devices are usually not meant to

provide 24/7 availability, but are designed towards

providing his user with the possibility to exploit

certain service, e.g. phone calls, short messages,

writing and receiving emails, … yield to the problem

that mobile devices might get switched off by the

user. Hence, the provided Web Service might not

only be available under different network addresses

but might not be available at all.

All these drawbacks can be solved by using the

here presented approach. By using the central proxy,

the service requests of a certain Web Service client

can be stored and if the mobile Web Service is

running, he can pull for service requests that of

interest to him. Since from a technical point of view

the Web Service provider only acts as a client to the

Web Service proxy, the potentially changing

network addresses of the mobile do not provide a

problem at all.

Furthermore, one of the major drawbacks of the

described polling mechanism can be limited by

adjusting the priority of the Web Service running on

the mobile device, resulting in a lower frequency of

the polling for the service request.

3 SCENARIO DESCRIPTION

The major idea for the implementation of the

middleware is to provide a Web Service proxy,

according to the proxy design pattern (Gamma et al.,

2005), in order for being able to overcome certain

problems in mobile scenarios as described by

(Svensson, 2009). One major problem here is that

mobile devices usually switch networks pretty often,

e.g. at home the mobile phone might be connected to

a WiFi network, at work the connection might be

established through another WiFi network and on

the way from work to home the mobile phone might

be connected to a GPRS/UMTS-network. Each of

these different networks, provide different IP

addresses and possibly different network

constellations, e.g. private IP addresses with network

address translation (NAT), where the Web Services

running on the device are not directly accessible

from the internet, or public IP addresses.

In order to overcome the problem of constantly

changing IP addresses, the presented approach

implements a Web Service proxy that dynamically

creates a proxy for each Web Service that gets

deployed on a mobile device. The created proxy

allows to receive service requests as a representative

to the actual service, store this service request along

with the necessary data. In the next step, the mobile

Web Service provider continuously polls for

requests to its services and sends the result back to

the dynamically generated Web Service proxy.

Afterwards the proxy send the result back to the

original client.

4 IMPLEMENTATION

The major goal of the work presented here is to

GETTINGSERIOUSABOUTPROVIDINGMOBILEWEBSERVICE

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provide a solution to the formerly described

scenario. Therefore, we implemented a middleware

that allows the provision of Web Services on mobile

devices. Here, the standard protocols (e.g. WSDL

for the description of the Web Service interface,

SOAP/REST as the standard network protocol and

http as the usual transport protocol) are used in order

to provide no additional effort on the client side for

requesting a mobile Web Service.

The following three sections provide a short

introduction to the services offered by the

middleware, afterwards the communication between

the mobile Web Service provider and the Web

Service client/consumer is described and last but not

least some details about the Java based

implementation for the test scenario are presented.

4.1 Communication between the

Mobile Web Service and Its Clients

In order to explain the communication that is

necessary for service request from the Web Service

client to the mobile Web Service provider, we

modelled the communication flow within the

sequence diagram shown in Figure 1.

Figure 1: The UML sequence diagram for the

communication between a Web Service provider and its

client.

First of all the mobile Web Service provider

needs to register its service with the Web Service

proxy. As part of the service registration process the

Web Service proxy creates the necessary data

structure for storing the service requests in the

database.

After the mobile Web Service provider registered

his service, it permanently polls the Web Service

proxy for new service request. The Web Service

proxy asks the database if a new service request for

the according mobile Web Service provider is

available and if so, returns the requests metadata to

the mobile Web Service provider. After receiving

the metadata of a new service request, the mobile

Web Service provider performs the service and

sends the result of the service to the Web Service

proxy that directly stores the result in the database.

From a client point of view, the Web Service

client simply calls the service provided by the Web

Service proxy. While receiving a new service

request, the Web Service proxy stores the necessary

request metadata in the database. Afterwards the

Web Service proxy directly starts to permanently

poll the database for the result of the according

service request. Once the mobile Web Service

provider has finished performing the request and

stored the result (via the Web Service proxy) in the

database, the Web Service provider is able to send

the result of the according service request back to

the client.

4.2 An Example Implementation

In order for being able to test the described approach

according to its performance, we implemented the

Web Service proxy in Java. Additionally, the mobile

Web Service provider was implemented for

Android. Here, we focused on an intuitive and easy

way for the implementation of the Web Service.

Therefore, we oriented ourselves on the JAX-WS

(Java API for XML-Based Web Services) described

in he Java Specification Request 224 (JSR 224).

Figure 2: UML class diagram of major parts of the

example implementation.

The major idea that we used from JAX-WS was that

a Web Service can easily be implemented by the use

of two different annotations: the

@MobileWebService annotation marks a class as a

Web Service and methods within this class can be

marked as methods available through the mobile

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Web Service with the help of the

@MobileWebMethod annotation.

The basic relationships between the major

classes of the example implementation are shown in.

For the sake of simplicity and transparency, less

important classes (and methods of each class) have

not been modelled.

Basically, the implementation consists of two

packages. One package that is usually deployed on a

server that is reachable from the internet via a public

IP address, this is the proxy package. Here, we find

one class that implements the necessary methods for

the registration of a new mobile Web Service, the

permanent polling from the mobile Web Service for

the service request metadata and the method that

allows to store the result of the service request in the

database. All of these methods are themselves

reachable as Web Services, so that the

communication between the instance running the

mobile Web Service and the Web Service proxy is

also completely Web Service based.

The provider package holds one of the major

classes, the MobileWebServiceRunner where the

mobile Web Service gets deployed to. This class is

comparable to an application server in usual Web

Service environments, but with a lower footprint.

This is extremely important to mobile devices due to

their limited resources. Additionally, this package

provides the two formerly mentioned annotations

allowing to make a class as a mobile Web Service

and accordingly a certain method of such a class as a

mobile Web Method. Last but not least, this package

also implements the ServiceRequestFetcher class.

This class inherits the java.lang.Thread class since

its responsibility is to permanently poll the Web

Service provider for new service requests.

5 CONCLUSIONS

The presented approach is capable of solving some

of the problems that usually occur while providing

Web Services on mobile devices, e.g. the problem of

permanently changing IP addresses. Furthermore,

the overhead that is inherent in the presented

approach does not seem to be a show stopper. As

shown, the performance in usually available mobile

networks like UMTS or GPRS, is comparable to

usual Web Service calls.

Therefore, it could be said that the presented

approach provides an interesting alternative to the

usual Web Service provisioning by mobile devices

where the mobile device acts as a server also from a

technical point of view. It eliminates certain

problems that usually occur if mobile devices

provide Web Service provider infrastructures, and

the resulting drawbacks from the performance point

of view are acceptable.

ACKNOWLEDGEMENTS

This work was partly supported by an Amazon AWS

research grant.

REFERENCES

AlShahwan, F., Moessner, K., 2010. Providing SOAP

Web Services and REST Web Services from Mobile

Hosts, In: Fifth International Conference on Internet

and Web Applications and Services (ICIW).

Gamma, E., Helm, R., Johnson, R., Vlissides, J., 1995.

Design Pattern – Elements of Reusable Object-

Oriented Software, Addison-Wesley.

IDC Worldwide Quarterly Mobile Phone Tracker, January

27, 2011.

Li, L., Chou, W., 2010. COFOCUS – Compact and

Expanded Restful Services for Mobile Environments,

In: Proceedings of the 7

International Conference on

Web Information Systems and Technologies,

Noordwijkerhout, The Netherlands

McFaddin, S., Narayanaswami, C., Raghunath, M., 2003.

Web Services on Mobile Devices – Implementation

and Experience, In: Proceedings of the 5

IEEE

Workshop on Mobile Computing Systems &

Applications (WMCSA’03), Monterey, CA

Srirama, S., Jarke, M., Prinz, W., 2006. Mobile Web

Service Provisioning, In: Proceedings of the Advanced

International Conference on Telecommunications and

International Conference on Internet and Web

Applications and Services (AICT/ICIW 2006),

Guadeloupe, French Caribbean

Svensson, D., 2009. Assemblies of Pervasive Services.

Dept. of Computer Science, Institutional Repository –

Lund University.

Tudor, B., Pettey, C., 2010. Gartner Says Worldwide

Mobile Phone Sales Grew 35 Percent in Third Quarter

2010, Smartphone Sales Increased 96 Percent,

Gartner, http://www.gartner.com/it/page.jsp?id=1466

313, last visited 19.11.2011

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