TECHNICAL CLASSIFICATION OF RUNTIME ENVIRONMENTS

FOR MOBILE APPLICATIONS

S¨oren Blom, Matthias Book, Volker Gruhn, Ruslan Hrushchak and Andr´e K¨ohler

Applied Telematics/e-Business Group, Dept. of Computer Science

University of Leipzig, Klostergasse 3, 04109 Leipzig, Germany

Keywords:

Mobility, Runtime Environments, Rich Internet Applications, Mobile Middleware.

Abstract:

This paper surveys the current state and the future of runtime environments suitable for developing Rich

Internet Applications for mobile clients. We compare the main characteristics of established technologies and

promising new developments, and assess their future potential. Furthermore, we consider middleware products

that provide an additional support layer solving typical mobility problems such as distribution, connectivity,

performance, reliability, etc.

1 INTRODUCTION

Current developments as well as recent experiences

with mobile applications lead us to the assumption

that the future of application development lies in Rich

Internet Applications (RIA). The term “Internet ap-

plication” emphasizes the fact that future applications

will be based on highly distributed components and

will be characterized by the intensive use of commu-

nication networks. Software will be mashed up with

third-party components and services at runtime, cre-

ating completely new applications ad hoc. The term

“rich” refers to the fact that applications will support

complex interaction patterns and advanced graphical

user interface (GUI) capabilities. This is a lot more

than the majority of today’s web applications provide,

which are still mainly based on static HTML.

Furthermore, application usage scenarios are also

changing radically. Especially the e-commerce ap-

plications on mobile devices will become increas-

ingly important. But mobility causes some major

concerns for application developers: a wide variety

of devices to support, unstable network connections,

limited bandwidth, high latency, security issues and

many more challenges need to be considered.

Thus, manufacturers and resellers of mobile de-

vices must decide how strongly the application devel-

oper should be supportedor restrained by the software

equipment pre-installed on the devices. They must

deﬁne which operating system and additional runtime

environment components should be installed on the

device, and howmuch inﬂuence the application devel-

oper should have on this conﬁguration. On the other

hand, application developers must choose a suitable

technology for implementing their application that is

compatible with target devices, highly ﬂexible, and

supports the development of state-of-the-art GUIs.

Considering this, an interesting question is which

runtime environments will be available in the fu-

ture for running mobile software clients, supporting

the “write once, run anywhere” paradigm, provid-

ing state-of-the-art GUIs and interaction capabilities,

as well as solving or masking known mobility prob-

lems (distribution, connectivity, performance, relia-

bility, and many more). In order to support this de-

cision process, this paper provides an overview of

current and future technologies positioned to address

these issues. In the following section, we identify dif-

ferent distribution patterns supported by different run-

time environments, and then discuss various runtime

environment technologies in detail (Sect. 2). After

summing up our ﬁndings, we discuss middleware ad-

dressing typical challenges found in the development

of mobile applications (Sect. 3). We conclude with an

evaluation of the presented technologies, and an out-

look on their future use (Sect. 4).

2 MOBILE RUNTIME

ENVIRONMENT

CLASSIFICATION

For the purpose of the following discussion, we deﬁne

a runtime environment as the set of components that

need to be present on a client in order to run appli-

153

Blom S., Book M., Gruhn V., Hrushchak R. and Köhler A. (2008).

TECHNICAL CLASSIFICATION OF RUNTIME ENVIRONMENTS FOR MOBILE APPLICATIONS.

In Proceedings of the Third International Conference on Software and Data Technologies - PL/DPS/KE, pages 153-158

DOI: 10.5220/0001879201530158

 SciTePress

asynchr.

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Operating

System

Runtime

Environment

GUI Logic

GUI Deﬁnition

Back-end

Services

Native Java ME

.NET

Compact

AJAX

Adobe

Flex

Open

Laszlo

Microsoft

Silverlight

APIs

Java ME

Runtime

.NET Compact

Runtime

XHTML

Java

Script

XHTML MXML

Java

Script

Java

Script

LZX

XAML

.NET

HTML

Pages

XmlHttp

Request

Flash

Plugin

AJAX /

Flash /

Silverlight

Plugin

Browser

CGI, PHP,

.NET, or Java

CGI, PHP

.NET, or

Java

Java EE Java EE

CGI, PHP

.NET, or

Java

Fat Client Applications

Traditional

Web Apps

Rich Internet Applications

ClientServer

Figure 1: Mobile Runtime Environment Classiﬁcation.

cations implemented using a certain technology. Fig-

ure 1 presents a classiﬁcation of the major players in

the ﬁeld of mobile runtime environments. As the ﬁg-

ure shows, we can distinguish several classes of ap-

plications by the kind of runtime environment they

require. We will give a short overviewof these classes

here, and then present the individual technologies in

the subsequent sections.

Fat client applications are applications that are

ﬁrst downloaded and installed on the client device.

The application then runs locally on the device. The

client is capable of some processing and potentially

even limited persistent storage. Installed applications

may be implemented directly on the device’s operat-

ing system as native applications, or on a generic run-

time environment such as Java ME or .NET Compact.

From a technical point of view, they are bound to a

certain technology and put a ﬁxed memory footprint

on the client, but do not need a permanent network

connection.

In contrast, web-based applications do not require

any downloads, but can be accessed just like a web

site. They form a special class of web applications

insofar as they need to take into account the limita-

tions that are unique to mobile devices, such as small

screen size.

Recently, these technologies have been adapted

with the aim to provide a richer, more responsive user

experience that is similar to desktop-based applica-

tions. These Rich Internet Applications (RIAs) are

based on technologies that provide(at least simulated)

asynchronous client/server communication, improved

usability and portability. They are characterized by

the following aspects (Duhl, 2003):

1. RIAs are executed within a particular runtime en-

vironment, i.e. a software infrastructure required

for the execution of the application that may of-

fer base services such as GUI rendering, security,

data and communications management.

2. The layout of user interfaces in RIAs is described

using declarative languages, while the functional-

ity of the interface (i.e. the interaction with the

user) is implemented in a scripting language.

3. The RIA’s business logic and back-end services

are typically implemented remotely on a central

server. This way, clients only need to handle

immediate user interaction, but can refer to the

server for all heavyweight processing and data

management.

Besides the bare AJAX technology, the major

players on the RIA market are currently Adobe with

Flash and Flex, Microsoft with Silverlight and Open-

Laszlo Systems with a product that generates code for

a number of these technologies.

2.1 Native Applications

Technically, the most straightforward way of devel-

oping a mobile application is by implementing it di-

rectly on the basis of the device’s operating system

(OS). Major products in this area are PalmOS, which

still has a signiﬁcant market share in the PDA market;

ICSOFT 2008 - International Conference on Software and Data Technologies

154

Windows CE, which is targeted to a number of em-

bedded device classes as diverse as PDAs, automotive

terminals and smart phones; and Symbian OS, which

has had a strong focus on telephony features from its

conception and comes in different “series” targeting

different handset classes. The LiMo Foundation, a

consortium of device manufacturers and network op-

erators, has recently begun efforts to deploy Linux-

based operating systems on mobile phones (LiMo,

2007). Last but not least, Google has announced the

Open Handset Alliance, an industry consortium of

more than 30 mobile technology companies who col-

laborate on the development of Android, an open and

comprehensive platform for mobile devices (Google,

2007a). Android will deliver a complete stack of soft-

ware for mobile devices: an operating system, mid-

dleware and key mobile applications. The Android

Software Development Kit (SDK) is open source; an

early version is already available.

Native applications are executable without the

need for a particular runtime environment, and poten-

tially run faster as they can directly access native fea-

tures of the device through the application program-

ming interface (API) of the operating system. On the

downside, this direct access to internals of the device

and operating system also elevates the security risks

for both the device and the application.

Since native applications need to be compiled for

a particular OS, they are typically not as portable as

applications built for a more generic runtime environ-

ment. In particular, different mobile OS may use dif-

ferent paradigms to achieve similar tasks such as dis-

play control, ﬁle management, multi-threading etc.,

some of which may even be entirely unsupported on

other devices. However, more recent OS develop-

ments such as Android or LiMo may ameliorate this

issue somewhat, as they speciﬁcally aim to provide

the ﬂexibility for making applications available across

a wide spectrum of devices.

2.2 Java Platform, Micro Edition /

Microsoft .NET Compact

Framework

The Java Platform, Micro Edition (Java ME) as a

runtime environment tailored to the special features

and restrictions of mobile devices. Microsoft’s .NET

Compact framework, a subset of the full .NET frame-

work also geared speciﬁcally to mobile devices, has

a very similar aim. Since both solutions are concep-

tually related, we will focus on Java ME in the fol-

lowing discussion. Our conclusions, however, can be

generalized for either framework.

Due to the power and memory limitations of

mobile devices, Java ME provides only the essen-

tial libraries and virtual machine capabilities (Helal,

2002a; Helal, 2002b). Applications developed using

this technology are deployed as so-called MIDlets,

which require (like all Java-based programs) a Java

Virtual Machine (JVM, or just VM) as their runtime

environment.

While Java ME beneﬁts from its relationship to the

desktop and server editions of the Java platform and

thus technically allows the reuse of code fragments

and developer skills, its portability is characterized

by the challenge of striking a balance between cater-

ing to the lowest common denominator of all mobile

devices, or tapping the potential of different device

classes’ features. This is not necessarily a fault of the

VM, but a consequence of the diverse range of capa-

bilities (such as display resolution and input modes)

offered by devices (Kochnev and Terekhov, 2003).

The approach to incorporate the Java VM directly

into the mobile phone’s operating system initially also

seemed like a viable alternative. However, develop-

ment of Sun’s own JavaOS, as well as the third-party

SavaJe OS, have recently been discontinued. The lat-

ter is currently being incorporated into Sun’s JavaFX

Mobile platform (Sun, 2007), a Java-based operation

and application environmentbased on a Linux OS that

is explicitly positioned for the development of Rich

Internet Applications. A more thorough evaluation of

this technology will be possible once JavaFX matures

from its current alpha development stage.

In contrast to most other runtime environments

discussed in this paper, Java ME has the beneﬁt of be-

ing independent of a permanent network connection,

as all necessary logic can be deployed on the client

device. It also beneﬁts from long-established devel-

oper skills and a wide spectrum of development tools.

As such, it is well-suited for rather isolated, compact

applications whose purpose does not hinge on a per-

manent network connection. Of course, this ease of

development and network independence comes at the

price of a comparably heavyweight runtime environ-

ment. However, for applications that rely heavily on

remote resources or content, and thus require a per-

manent network connection by virtue of their appli-

cation domain anyway, Java ME cannot keep up with

the ﬂexibility and small footprint that the runtime en-

vironments for RIAs offer.

2.3 AJAX

Since a few years, interest in a new class of dynamic

web applications has surged, largely fueled by the

Web 2.0 hype: By using a combination of estab-

lished web-based technologies, developers are cre-

TECHNICAL CLASSIFICATION OF RUNTIME ENVIRONMENTS FOR MOBILE APPLICATIONS

155

ating applications with a look and feel that resem-

bles desktop-based interaction patterns much more

than the usual page-centric paradigm. Collectively

termed AJAX (Asynchronous JavaScript and XML)

(Paulson, 2005), these technologies effectively hide

the request-response communication taking place be-

tween client and server, and instead present users with

a self-contained, highly responsive interface that al-

lows them to manipulate and interact with the content

directly.

To achieve this, AJAX applications rely on a num-

ber of prerequisites. To circumvent the interactive

limitations of HTTP, AJAX applications employ fair

amounts of JavaScript to control the behavior of the

user interface and implement minor application tasks.

This presentation logic communicates with the server

by exchanging HTTP requests that are extended over

long periods of time to achieve the illusion of asyn-

chronous communication.

The technologies that jointly constitute what may

be called the “runtime environment” for AJAX ap-

plications are meanwhile incorporated in all major

web browsers. Experiences with running AJAX ap-

plications on mobile phones are still quite limited

– while technically feasible on sufﬁciently equipped

smart phones, it may be a challenge to carry the us-

ability of AJAX applications (which tend to make ex-

cessive use of the direct manipulation paradigm) over

to mobile phones with their limited display and input

capabilities. On the other hand, the iPhone’s multi-

touch display is a prime example of the usability po-

tential inherent in direct manipulation interfaces – if

device manufacturers are willing to give up the tradi-

tional ten-button/two-softkey input paradigm.

Regarding future developments, it seems likely

that AJAX will continue to enjoy high popularity

among developers and end-users. Its major advan-

tage over other approaches is the dependency on just

a very basic set of technologies that are built into

any modern web browser, so it requires zero installa-

tion. On the other hand, it must be noted that the im-

plementations of different web browsers may contain

enough subtle differences to make the development

of complex portable AJAX applications a non-trivial

challenge. The independence from a dedicated run-

time environment makes AJAX especially attractive

for mobile devices, as it does not introduce a persis-

tent memory footprint of its own, and it can be exe-

cuted in a controlled environment that is unlikely to

expose the handset or network to serious threats.

2.4 Adobe Flash / Flash Lite

Adobe Flash (formerly Macromedia Flash) is a pop-

ular proprietary technology for the development of

multimedia content that has been around for a long

time by now. The runtime environment for Flash

applications is the Flash Player, which is executed

within a web browser. Through its combination of

media content with programming logic, Flash is es-

pecially suited for the multi-medial representation of

complex processes. With the help of ActionScript,

it is possible to implement online games, multimedia

tutorials, and A/V streaming.

For mobile devices, the Flash Lite technology has

been derived from the basic Adobe Flash, and opti-

mized to achieve a more lightweight runtime envi-

ronment in terms of ﬁle size, memory footprint and

performance requirements. A disadvantage of Flash

technology may be that its authoring tools are more

geared towards designers than developers, and that

the ﬁle format is proprietary. However, the multime-

dia capabilities and its installed base are virtually un-

paralleled, with many popular Web 2.0 applications

using Flash technology. In the mobile world, Flash

Lite is also quite well established (Adobe, 2007).

2.5 Adobe Flex

Adobe Flex is a development framework that strives

to make the traditionally designer-centric Flash tech-

nology more accessible to software developers by en-

abling them to build RIAs based on Flash technol-

ogy. A Flex application is developed using the pro-

gramming language MXML for the description of the

user interface, and ActionScript for the implementa-

tion of the client-side logic. The Flex compiler will

then translate this code into Flash bytecode that can

be executed by any Flash runtime environment. Flex

can be especially attractive as a front-end for complex

information systems, where the business logic can

be implemented using Java EE on the server, which

communicates with the Flex front-end through the so-

called Flex LifeCycle Dataservice.

The use of Flex offers the advantage that the im-

plementation of the presentation logic on the client al-

lows for a highly responsive user interface, while the

server-side business logic has easy access to back-end

systems.

2.6 Microsoft Silverlight

Silverlight (Microsoft, 2007) is Microsoft’s attempt

to introduce a browser extension into the market that

ICSOFT 2008 - International Conference on Software and Data Technologies

156

shall provide the capabilities of the Windows Presen-

tation Foundation (WPF) to arbitrary platforms.

Silverlight consists of a browser plug-in which

also includes a runtime environment for .NET (the

.NET Framework for Silverlight) in version 1.1. Us-

ing the Silverlight technology, WPF user interfaces

can be realized as RIAs, which would enable large-

scale reuse of application paradigms know from the

Windows world. GUIs are described declaratively us-

ing the open and standardized XAML language, while

different programming languages can be used to im-

plement the GUI logic. Client-server communication

is realized using JavaScript (similar to the AJAX ap-

proach); from version 1.1, limited .NET support for

web services is also available. Since all GUI code is

executed on the server and all communication is con-

ducted across web services, there are no prerequisites

as to which server platform should be employed.

Since Silverlight is still a young technology, dis-

advantages are its relative immaturity and sparse in-

stalled base among end-users. Silverlight support is

still low in the mobile realm: Microsoft provides Sil-

verlight runtime only for Windows Mobile platform.

2.7 OpenLaszlo

OpenLaszlo (Laszlo, 2007) is another platform for the

creation of Rich Internet Applications. The technol-

ogy is freely available as open source software under

the Common Public License.

The architecture is similar to Adobe Flex in that

it does not require a runtime environment of its own,

but employs existing runtime technologies: The GUI

description and logic are encoded in the XML-based

LZX format, which is translated by a compiler into

Flash bytecode or DHTML. Either of these represen-

tations can be presented in a browser by clients. In ad-

dition, it is possible to generate applications for other

runtime environments such as AJAX or Silverlight.

Beneﬁts of OpenLaszlo applications are the use

of an open, declarative language, which offers a great

selection of standard GUI components, and the pos-

sibility to integrate it with server-side business logic

implemented in Java. However, developers need to be

aware of potential restrictions imposed by different

target platforms that the OpenLaszlo application may

be compiled to. Still, OpenLaszlo is attractive due to

its support of different target runtime environments.

3 MIDDLEWARE FOR MOBILE

APPLICATION SUPPORT

Runtime environments for mobile applications, and

especially technologies for RIAs, have the potential

to open up a large universe of information to users

through lightweight user interfaces. However, their

network dependence makes them prone to temporary

losses of connectivity, which may lead to anything

from erratic application behaviour to loss or corrup-

tion of back-end data.

To ameliorate these problems that typically plague

mobile applications, a number of middleware solu-

tions exist that decouple the client- and server-side

processing logic from the network by providing trans-

parent caching and synchronization services. In Fig.

1, these middleware implementations would be de-

ployed on a client layer just below the web browser,

where they can transparently manage the cooperation

with remote components and handle communications

with the server.

The recently-introduced Google Gears framework

provides a mechanism for continuous execution of

AJAX-based applications even under unstable net-

work conditions (Google, 2007b). It serves as a data

management layer between the client-side applica-

tion UI and the client’s network layer. This data

management layer comprises a connectivity switch,

caching/synching logic and local database. In con-

nected operation, Google Gears will transparently

pass all data between client and server, while keeping

the local background database up-to-date with this in-

formation. When the network connection is lost, the

connectivity switch will reroute all read/write oper-

ations from the application UI to the local database,

which should be able to answer most requests for

data, and can cache all data updates. Once the connec-

tivity has been restored, the local database is synchro-

nized with the server, and the regular connected op-

eration resumes. The effectiveness of Google Gears’

masking of connection losses depends heavily on the

application domain and its reliance on external real-

time information.

For more heavyweight mobile applications, a

number of middleware solutions exist that support

disconnected operation, caching/replication, and con-

ﬂict resolution. Among the most interesting prod-

ucts are XMIDDLE (Mascolo et al., 2002) and OSGi

(OSGi, 2007), two Java-based middleware implemen-

tations.

As a ﬁnal example, the MobCo middleware

(Gruhn and Sch¨afer, 2007) currently developed by the

Applied Telematics/e-Business Group at the Univer-

sity of Leipzig in cooperation with Deutsche Telekom

TECHNICAL CLASSIFICATION OF RUNTIME ENVIRONMENTS FOR MOBILE APPLICATIONS

157

Laboratories strives to increase application availabil-

ity and ubiquitous usage scenarios for mobile clients.

MobCo offers a middleware and framework for the

development of components that are able to run both

on the server and the mobile client, but whose actual

execution location is determined at runtime. As the

middleware is context-aware (regarding mobile hard-

ware, network situation and application status), com-

ponents are able to migrate from server to client or

vice versa, depending on where they can experience

better performance or increase system availability (in

situations where the mobile client needs to switch to

ofﬂine mode). This is combined with a persistence

layer that is able to store and retrieve data from either

local or remote locations transparently to the applica-

tion. The optimal execution location for components

will be determined through simulation, which will en-

able derivation and evaluation of component migra-

tion strategies. With such ﬂexibility in the applica-

tion’s architecture, the MobCo middleware will allow

distributed applications to cope much better with the

heterogeneous and ever-changingconditions (in terms

of network infrastructure, hardware, etc.) of mobile

software, and thereby expand the number of contexts

in which an application can successfully be run with-

out having to write it more than once.

4 CONCLUSIONS

Our comparison of runtime environments shows that

the future of mobile application development lies

in Rich Internet Applications, which are based on

highly distributed components and characterized by

the intensive use of communication networks, com-

plex interaction patterns and advanced GUI capabil-

ities. In contrast, fat client applications built as Java

ME, .NET Compact or native applications can make

a more efﬁcient use of system resources and depend

less on a permanent network connection. However,

they are lesser platform independent, as their close-

ness to the underlying system causes distribution and

compatibility issues.

The more promising way for mobile devices thus

seems to be reliance on the above-mentioned RIA

technologies. AJAX is a prominent representative of

this approach, as the fast-growingamount of commer-

cial applications with this basis shows. From a soft-

ware process perspective, OpenLaszlo showswhat the

future of Rich Internet Application development may

look like: an open, declarative language that enables

the generation of GUIs for different runtime environ-

ments and the opportunity to smoothly integrate it

with server-side business logic.

Finally, it is important to consider emerging spe-

ciﬁc middleware products for use in mobile environ-

ments. They are solving the typical mobility prob-

lems, which are of particular relevance when develop-

ing applications for demanding businesses use cases.

In combination, open and highly ﬂexible technologies

for lightweight GUI development as well as highly

specialized middleware products will be the crucial

tools for developing the mobile Rich Internet Appli-

cations of tomorrow.

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