Service-oriented Platform for Virtual Reality Application Development

Evandro César Freiberger

1,2

, Ricardo Nakamura

and Romero Tori

PCS/POLI/University of São Paulo, São Paulo-SP, Brazil

DAI/Federal Institute of Mato Grosso, Cuiabá-MT, Brazil

Keywords:

Virtual Reality, Reuse, Interactive Content, Service-oriented Computing.

Abstract:

An important contemporary fact is the advent of Web 2.0, mainly characterized by the possibility of content

being produced collaboratively, empowering and enabling the concept of collective intelligence. Another

important feature is the popularity of virtual communities, which allow people around the world to exchange

information and experiences. In order to increase the potential for reuse and sharing of interactive content, this

paper proposes an architectural model for a software platform that enables the online production and execution

of virtual reality applications as well as sharing of interactive content. The remote online environment,

associated with the capacity to represent and store 3D interactive content, enables the sharing and reuse of

such content in the production of virtual reality applications. The paper we present the description of the main

elements of the proposed architectural model and results of the research. The results point to the feasibility of

the proposed model.

1 INTRODUCTION

Web 2.0 has changed the traditional model of

information publishing on the Web to a model of

collaborative information production. Nowadays

people extensively use Web 2.0 applications such as

Wikipedia, YouTube, LinkedIn, MySpace, Twitter,

Facebook and Google Applications to create and

share information. Web 2.0 has changed the way

people consume information and knowledge into a

collaborative approach (Bein et al., 2009).

Virtual reality (VR) is used in the production of

complex virtual environments (VE), using non-trivial

input and output devices to provide users with a

sense of immersion in real-time synthetic worlds. In

the particular case of software development for VR

application, the need for reuse is enhanced by factors

characteristic of this kind of application.

A predominant feature of VR systems is

the dependence on computing resources and

unconventional devices, such as special data input

devices, special viewing equipment, along with the

high computational power, especially with graphic

processing. New techniques have alleviated this

problem through the development of interactions

that exploit gestures and sound commands, as an

alternative control of virtual environments.

In order to reduce dependence on special input

and output devices, computational resources such

as graphic processing and enable the production

of VR applications in a collaborative production

environment, this paper proposes a software platform

that combines the features of Web 2.0 and the

of service-oriented computing model. The goal

is to enable the production, reuse and execution

of VR application elements in a distributed online

environment.

2 BACKGROUND

2.1 Virtual Reality

With the development of VR and the advancement of

computational resources, interactive and immersive

representations become easier to obtain. The

interfaces are more intuitive and break the boundaries

of computer screens, keyboard and mouse, allowing

users to act in a three-dimensional space.

VR is an advanced interface for computer

applications will be considered. It allows the user

to move (navigation) and interact in real-time in

a three-dimensional environment, making use of

multi-sensory devices, to act or feedback (Tori and

Kirner, 2006).

With VE created from the use of VR, humans

196

Freiberger E., Nakamura R. and Tori R..

Service-oriented Platform for Virtual Reality Application Development.

DOI: 10.5220/0004895301960203

In Proceedings of the 9th International Conference on Evaluation of Novel Approaches to Software Engineering (ENASE-2014), pages 196-203

ISBN: 978-989-758-030-7

 2014 SCITEPRESS (Science and Technology Publications, Lda.)

senses and abilities can be expanded, permitting to

see, hear, feel, drive and travel far beyond the natural

capacity. It creates alternatives for the production

of applications related to entertainment, simulations,

training and education.

2.2 Service-oriented Computing

Service-oriented computing (SOC) involves concepts

originating from a variety of disciplines, such

as distributed computing systems, computer

architectures and middleware, grid computing,

software engineering, programming languages,

database systems, security and knowledge

representation (Papazoglou and Heuvel, 2007).

Currently, the technical solution mostly adopted

for the development of services-oriented computing

is Web Services (Erl, 2009), (Papazoglou et al.,

2008). The strong adoption of Web Services

is a result of its characteristics, among which

we can highlight: platform independence and

programming languages, the possibility of exposing

any application functionality as a service over the

Internet and the use of open standards. According

to Wang and Qian (Wang and Qian, 2005),

implementing distributed computing via the Web

Services technology, has the following advantages:

increases the portability and interoperability of

distributed computing; increases the reusability

and scalability of distributed components; reduces

the complexity of composition and deployment

of components; simpliﬁes management of the

distributed system and facilitates the publication of

the legacy code through distributed service interfaces.

Another important factor for the adoption of Web

Services is the existence of a speciﬁcation controled

by a consortium which makes it less vulnerable

to particular issues of either implementation

(Papazoglou and Heuvel, 2007).

3 RELATED WORK

To support the objectives of this research, we

conducted a literature review aimed at identifying

software platforms that support the development

of VR applications, with emphasis on the reuse

of software components, in particular using the

services-oriented computing approach.

The authors Zang and Gracanin (Zhang and

Gracanin, 2008), propose a framework to build

applications on a multi-user virtual environment,

integrating content via distributed services. In

addition, they propose the use of stream for

applications feedback transfer to overcome the

performance limitations of Web Services messages.

The overall architecture of the framework is based on

distributed components integrated through services

and execution control based on events.

Shao and McGraw (Shao and McGraw, 2009)

proposed a framework named Service-Oriented

Embedded-Simulation Software (SOESS), which

combines COS and Cloud Computing to produce

military simulation, through the components

composition. The goal of the framework is to

ensure that applications developed from it are

highly interoperable with other applications, systems

and platforms, particularly with legacy software.

The components communicate via Web Services,

ensuring greater interoperability.

The authors Filho et al. (Filho et al., 2011)

propose a platform for development of virtual

environments called Hydra. Hydra is composed

of a set of frameworks and tools with the purpose

of facilitating and accelerating the applications

development. The applications development is

accomplished by means of plugins that allow you to

customize the behavior of particular applications.

The work of Chevaillier et al. (Chevaillier et al.,

2012) is proposed a methodology and a framework to

design semantic VR environments. The development

of VR applications is done through an approach based

on models created with a specialization and extension

of the Uniﬁed Modeling Language (UML). This

modeling covers aspects of semantic representation

of VE, such as: domain ontology, the structure of the

environment, the behavior of entities and interactions

between agents and activities.

The vast majority of studies analyzed propose the

reuse of software elements for the development of VR

applications through the incorporation of portions of

specialized code, for example, using API components

or the extent of frameworks. This paper proposes a

model of representation of applications that enables

the production of VR applications with high-level

representation, without the need for coding and

compiling. The difference lies in the ability to provide

such functionality through services. This enables

different technologies (programming language and

execution platform) to be used for the development

of applications production and running environments.

4 ARCHITECTURAL MODEL

In this work, we use the paradigm of service-oriented

computing. This model is capable of being totally

produced and executed in a remote environment. The

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speciﬁed platform is characterized as a service bus

that provides the capacity to produce and execution

VR applications, in a distributed online environment.

4.1 Subsystems Architecture

The logical view of the platform elements, illustrated

in the Figure 1-B, consists of four subsystems

and their dependency relationships. The following

subsystems are described:

Figure 1: Platform Logical View.

• Virtual World Production Subsystem - has the

functionality to create, update, delete and reuse

elements of VR applications. A VR application

is composed of one virtual world, one or more

scenes, which are composed of virtual objects,

behaviors and appearance characteristics;

• Virtual World Execution Subsystem - provides an

execution context for the applications produced

on the platform. An execution context consists of

user context, input devices, output devices, a VR

application and resources;

• Access Subsystem - gathers the features that

enable access control and authorization for

platform users. Besides the management of

users, the subsystem provides authentication and

veriﬁcation services of authorizations to other

subsystems of the platform;

• Resource Subsystem - gathers management

features, searches for and rescues resources

used in the production and execution of VR

applications such as: images, sounds, videos, 3D

object models and textures.

As can be seen in Figure 1-B, the production

subsystem uses the services of the access and

resource subsystems. It is also possible to

observe that the execution subsystem uses the

services of the resource, access and production

subsystems. The subsystems were designed with this

distribution of responsibilities to allow deployment in

different servers, with adequate computing resources

according to the characteristics required by each

subsystem.

Figure 1-A illustrates the client-side of the

platform, potentially consisting of several production

environments of VR applications. The client

applications use Web Services to create, seek and

save elements of applications in the repositories of

the platform. Each production environment can use

different representations and models of interaction

with the end user.

Communication between production

environments (client-side) and the platform

(server-side) is performed by means of Web Services,

through which data (entities) that represent resources

(e.g. images, sounds, textures), virtual objects, scenes

or virtual worlds are sent and received.

Figure 1-C illustrates the client-side of the

platform responsible for the interaction and viewing

of the server-side execution. The execution

environments (client-side) capture data and events

from input devices and send them through Web

Services to the execution context of the server-side.

From the deﬁnition of subsystems, an

architectural model was produced to be used as

the basis for the subsystems. The goal was to deﬁne

an architectural model that could be adopted for

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all subsystems to facilitate the understanding and

implementation of subsystems. The next section

presents the elements of this architectural model.

4.1.1 Subsystems Logical Architecture

Each subsystem consists of three components: a

Service to expose the functionalities of the subsystem,

a Domain that implements the functionalities and

a Repository that stores information related to the

subsystem.

Figure 2: Domain Component Logical Architecture.

Figure 2 highlights the standard architecture

deﬁned for the subsystems Domain component. The

subsystems’ Domain component is divided into three

layers of abstraction; they are:

• Persistence - consists of classes that are

responsible for the persistence and recovery

of entities of the subsystem. This layer is

responsible for the implementation of the

object-relational mapping (MOR) of the entities

deﬁned in the subsystem domain layer, isolating

this action from the rest of the subsystem (Matic

et al., 2004). The persistence layer uses the

architectural pattern of data sources called Table

Data Gateway (Fowler, 2003).

• Domain - consists of two groups of classes,

domain and entity. Domain classes contain the

logic of the subsystem. Entity classes represent

the domain model of the subsystem, using the

paradigm of object orientation. These classes

represent the information and their relationships.

The domain layer uses the architectural pattern

known as Domain Model (Fowler, 2003).

• Facade - represents the subsystem interface,

deﬁned by classes that combine the public

functionality of the subsystem. It aims to

hide the complexity of the subsystem and to

abstract class responsibilities that make up the

subsystem. This layer should be implemented

using the architectural pattern for domain logic

named Service Layer (Fowler, 2003).

The Repository component consists of a

Relational Database Management System (RDBMS)

used for the subsystem’s data persistence. Each

subsystem has its own RDBMS due to the distributed

architecture of the subsystems.

The Service component is formed by the Web

Services that expose the capabilities of the subsystem.

The services of each subsystem can be consumed

by other subsystems of the platform or by external

applications.

4.2 Application Representation

In this study we used the paradigm of object

orientation associated with the paradigm of

service-oriented computing to conceive a platform

to build and run VR applications on a remote

environment. Also proposed a model to represent VR

applications. This model is capable of being totally

produced and executed in a remote environment.

The representation model illustrated in Figure 3,

modeled and implemented through the paradigm of

object-oriented development allows instances of these

objects to be remotely created, edited and persisted

through service interfaces.

On the platform, a VR application consists of a

virtual world (VirtualWorldVO), one or more scenes

(SceneVO), which are composed of virtual objects

(VirtualObject3DVO) and appearance characteristics

(AppearanceVO, MaterialVO and TextureVO). Virtual

worlds, scenes and virtual objects are created and

maintained independent, allowing them to be reused

to compose other scenes and virtual worlds.

Besides the representation of the static elements

that make up the VR applications, elements of

the dynamic characteristics of applications are also

represented the. The behavior of the applications is

represented by the elements related to the association

of inputs (InputVO), events (EventVO) and behaviors

(BehaviorVO). Events can be generated by means

of data entry services (InputEventVO), depending

on time (TimerEventVO) or caused by events that

occur directly with objects in the virtual world

(Object3DEventVO).

Figure 4 shows the production of applications on

the platform. The aim is to discuss the potential for

reuse of the key elements that can compose a VR

application produced on the platform. It is possible

to observe the symbolic representation of four VR

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Figure 3: Application Representation Model.

applications produced by the combination of the other

elements present in the repositories of the platform.

In the hierarchical representation model of the

proposed application, reuse can occur at four levels:

1. the Resource element (3D models, images,

sounds, videos) can be reused to deﬁne the virtual

objects or scenes, for example, a virtual object

that accesses a ﬁle with 3D representations, an

image that is used as texture of a virtual object.

This is illustrated in Figure 4 by the elements R3

and R4;

2. the VirtualObject element that can be reused to

make various scenes. This is illustrated in Figure

4 by Ob2, Ob3 and Ob4 elements;

3. the Scene element may be reused to form different

virtual worlds. This is illustrated in Figure 4 by

S1, S3 and S4 elements;

4. the VirtualWorld member can be reused to write

different applications. This is illustrated in Figure

4 by the VW2 element.

The capability to be reused is not only restricted

Figure 4: Levels of Reuse in Applications Production.

to the structure and appearance characteristics of

the application. The behaviors associated with

VirtualObject, Scene and VirtualWorld elements are

automatically reused, as part of the deﬁnition of these

elements.

4.3 Production Subsystem

In this article, the VR applications production

subsystem, consisting of components

such as VirtualObjectProductionManager,

SceneProductionManager,

VirtualWorldProductionManager and

ApplicationProductionManager, has been detailed.

Each component has its own service that exposes

its functionality through service interface. Figure

5 illustrates the main classes of the production

subsystem.

As described in the previous section, each

production subsystem component has a service that

exposes its functionality. Figure 5 illustrates, as

an example, the application production service

named ApplicationProductionService. The

ApplicationProductionService service exposes the

functionality of the ApplicationProductionManager

domain class responsible for the inclusion, change,

deletion and retrieval of ApplicationVO instances of

the applications repository. The ApplicationDAO

class is responsible for object-relational mapping of

ApplicationVO instances.

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Figure 5: Production Subsystem.

5 ARCHITECTURE VALIDATION

A VR applications production environment prototype

was developed, as can be seen in Figures 6, 7, 8 and

9. The development of this software prototype had

two aims: 1) to evaluate the model representation,

editing and reuse of elements of VR applications in

the designed remote environment, and 2) to evaluate

the service interface provided by the VR applications

production subsystem. The production environment

prototype allows to create and edit four elements that

constitute a VR application as well the Application

element itselfas according to the representation model

illustrated in Figure 3.

Figure 6: Prototype of a Production Client - Virtual Object.

Figure 6 illustrates the editing screen of the

VirtualObject element. This element represents the

virtual objects that can be deﬁned into 3D models by

means of reference Resource ﬁles, or by deﬁnition

of geometric shapes or by composition of more than

one virtual object. In this case study, the virtual

objects were produced by reference to the Resource

element previously inserted in the repositories. Figure

10 shows the inserted virtual objects in the case

study: Bladder-VO, Uterus-VO, LeftOvary-VO and

RightOvary-VO.

Figure 7 illustrates the editing screen of the Scene

element. This element represents the scenes that

are used to compose different virtual worlds. A

Figure 7: Prototype of a Production Client - Scene.

scene element can contain multiple VirtualObject

elements previously inserted in the repositories of the

platform. Besides the virtual objects, ambient light,

directional lights, geometric transformations, events

and respective behaviors are deﬁned. Figure 10 shows

scenes inserted in this case study: Scene01, Scene02,

Scene03, Scene04 and Scene05.

Figure 8: Prototype of a Production Client - Virtual World.

Figure 8 illustrates the editing screen of the

VirtualWorld element. This element represents the

virtual worlds that are used to compose different

applications. A VirtualWorld element can contain

multiple Scene elements previously inserted in the

repositories of the platform. Figure 10 shows

the inserted virtual worlds in this case study:

VirtualWorld01, VirtualWorld02 and VirtualWorld03.

Figure 9 illustrates the editing screen of the

Application element. This element represents the

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VR applications produced on the platform. An

Application element must contain a VirtualWorld

element previously inserted in the repositories of the

platform. Figure 10 shows the inserted applications

this case study: Application01, Application02,

Application03 and Application04.

Figure 9: Prototype of a Production Client - Application.

The prototype presented consumes services

provided by the platform subsystems, allowing these

elements to be created, edited or deleted. Different

production environments can be developed to suit

different levels of users. Another important aspect is

that due to the fact that the platform offers services

such as Web services, different implementation

technologies can be used for the development of

production environments. These environments can

be produced in different programming languages and

execution platforms.

Figure 10: Case Study Elements.

Besides the application production prototype, a

prototype for a VR application execution environment

was developed, created through the production

prototype. Figure 11 shows the three screens of

the implementation prototype. The ﬁrst (top) is the

interface used to locate the application to be run

and the second and third (middle and bottom) shows

the feedback of the execution of the application on

Figure 11: Prototype of a execution client.

the server side. In this ﬁrst prototype, feedback is

obtained by successive calls to the service which

returns frames that represent the rendering that occurs

on the server.

Once these critical points have been validated, the

design of the platform enters a phase of development

and deployment, where all the functionality of the

subsystems will be implemented for deployment and

delivery of the platform in a production environment.

Aspects of performance and robustness of the

platform will also be considered.

6 CONCLUSIONS

The proposed architectural model using the paradigm

of service-oriented computing allows any application

that is capable of invoking Web Services to

consume the services offered by the platform. The

representation model of VR applications presented

allows instances of virtual objects, scenes, virtual

worlds and applications to be created and edited

remotely via Web Services interface.

The representation of VR applications in an

online environment allows interactive content to be

shared and reused to produce new VR applications.

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Reducing dependence on special features such as

graphic processing, high volume storage devices and

speciﬁc input, extends the possibilities of platforms

used as clients. With the holding of the execution

of applications on the server platform, it is possible

to reduce the requirements of these resources on the

client-side. The use of a service-oriented model

allows any computing environment (desktop, Web

or mobile devices) to be used to host applications

consuming the platform service.

The prototyping of the production and execution

subsystems on the server-side, together with

the prototyping of the production and execution

environments on the client-side, made it possible

to assess the viability of the proposal. Despite the

limitations of the prototype, it was possible to verify

the efﬁciency of the VR applications representation

model and remote services offered by the platform,

allowing the production, storage, reuse and execution

of VR applications in a remote and collaborative

environment.

As future work can be considered the development

of production and execution environments to run

in an Web platform, deﬁnition of a iconographic

representation of VR application elements, should

also be treated the performance and robustness

aspects of the platform, expanding the possibilities

of applications representations that require response

low-latency.

ACKNOWLEDGEMENTS

The authors thank CAPES, the Brazilian government

entity dedicated to the training of human resources

and FAPEMAT, Foundation for Research Support

of the State of Mato Grosso, for providing support

towards the viability of the EPUSP/UFMT/IFMT

agreement for the completion of the PhD on which

this work is based.

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