CONTRIBUTION TO THE REQUIREMENTS ENGINEERING OF

VIRTUAL ENVIRONMENTS

Tereza G. Kirner

, Valéria F.M. Salvador

and Claudio Kirner

Methodist University of Piracicaba, Rodovia do Açúcar, Km 156, Piracicaba, SP, Brazil

University of São Camilo, Av. Nazaré, 1.501 – Ipiranga, São Paulo, SP, Brazil

Keywords: Requirements engineering, Virtual environments.

Abstract: This paper aims at contributing to the requirements engineering of virtual environments. Requirements

engineering is characterized by a process composed of the phases of elicitation, specification, and

evaluation, based on concepts from the software engineering area and on experience obtained through the

development of virtual environments. The requirements engineering process is described and exemplified

and the main conclusions are pointed out.

1 INTRODUCTION

Virtual Reality (VR) is an advanced interface

technology that enables the user to use the software

system as well as to perceive himself/herself inside

of the three-dimensional computer generated

environment. In this context, the user can explore

the virtual environment, what is made possible

through navigation, interaction and immersion

techniques (Vince, 2004).

Like for any software system, it is necessary to

define the virtual environment requirements

appropriately. However, the VR area is still very

recent, and does not count on enough studies on

requirements engineering for virtual environments

and applications. (Kim, 1999). The need to better

understand and specify the requirements of such

applications motivated this work.

This article intends to contribute for the

requirements engineering of virtual environments. A

process is presented, defined with basis on concepts

from software engineering and complemented by

contributions from experiences obtained through the

development of several virtual environments.

Section 2 summarizes virtual reality and

requirements engineering concepts; section 3 details

the requirements engineering process, applied to the

development of virtual environments; and the

conclusions are presented in section 4.

2 CONCEPTUAL FOUNDATIONS

2.1 Virtual Reality and Virtual

Environments

Virtual reality is a strong tendency in human-

computer interfaces (Myers, 1996). It is a

technology able to provide to the user immersion,

navigation and interaction in a three-dimensional

computer generated environment, using, for that,

multi-sensorial channels as vision, touch and

audition (Stuart, 1996; Vince, 2004). Besides the

keyboard and mouse, the user can use special

devices as gloves, head mounted displays, space

balls, joysticks, etc., that generate a "presence"

sense, which is a very important requirement of

virtual environments. Those devices, associated to

techniques and computer languages, make possible

the user to interact with the application, allowing the

exploration of the virtual environment and the

modification of objects in an easy and fast way - for

instance, showing, dragging, rotating and visualizing

objects under different view points.

An environment represents a certain space and

situation, including all its components, conditions

and objects. A virtual environment is an interactive

environment, generated by computer in a VR system

(Kirner; 1999; Kirner 2001).

142

G. Kirner T., F. M. Salvador V. and Kirner C. (2007).

CONTRIBUTION TO THE REQUIREMENTS ENGINEERING OF VIRTUAL ENVIRONMENTS.

In Proceedings of the Ninth International Conference on Enterprise Information Systems - HCI, pages 142-147

DOI: 10.5220/0002351701420147

 SciTePress

2.2 Requirements Engineering

Requirements represent the software system needs

and the constraints imposed on it. A requirement is a

condition or necessary capacity for a user to solve a

problem or reach an objective, concerning the

problem domain. Requirements engineering involves

the universe of information that compose the system

and all its stakeholders (Sommerville, 1997).

Requirements engineering is an essential phase

of the software system development process, that

comprises a complete definition of the external

behavior of the system, in terms of functional and

nonfunctional requirements. Several studies have

been pointed out that the inadequate definition of

requirements is responsible for a significant part of

defects in the software. The elimination of these

defects becomes more and more difficult and costly

as the software development process goes to its

subsequent phases of project and implementation

(Kirner, 1996).

The main phases of requirements engineering

are: elicitation, specification, and validation (Castro,

1995; Kirner, 1999). Such phases will be

summarized in the next section.

3 REQUIREMENTS

ENGINEERING PROCESS FOR

VIRTUAL ENVIRONMENTS

The process here described is based on software

engineering concepts (Sommerville, 1997), which

were adapted and complemented from a series of

lessons learned through the development of various

virtual environments, including those presented next.

• VE-Museum (Virtual Environment of

Museum). It was developed to represent a

Historical Museum, which is a cultural place

for public visitation. This place has

collections of objects and historical

information (Kirner, 1999). Figure 1 presents

a view of that museum.

• VE-Capoeira (Virtual Environment of

Capoeira). It was developed as part of a

collaborative virtual environment for

educational purposes, implemented as a

distributed, multi-user system (Kirner, 2001).

Figure 2 shows a scene modeled for the VE-

Capoeira.

• VE-Engineerig (Virtual Environment for

Engineering). It was developed to give

support to the remote use of a Coordinate

Measuring Machine (CMM), used in the

construction of high precision mechanical

parts (Calonego, 2004). Figure 3 illustrates

the MMC, in a virtual reality scenery.

Figure 1: Virtual Museum.

Figure 2: Capoeira Scene.

Figure 3: Coordinate Measuring Machine.

Z axis

X axis

B axis

A axis

Touch

probe

Y axis

CONTRIBUTION TO THE REQUIREMENTS ENGINEERING OF VIRTUAL ENVIRONMENTS

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3.1 Requirements Elicitation

The elicitation phase involves actions that aim to

capture and register information that will help in the

complete and correct understanding of the user

needs and expectations (Castro, 1995; Sommerville,

1997). The requested tasks can become complex,

since the stakeholders have experiences, knowledge,

previous concepts and different terminologies.

For the three considered virtual environments,

requirements elicitation applied techniques

traditionally used in the development of other types

of applications, such as: observation, interviews,

meetings, besides the identification and analysis of

pertinent documentation. In this context, three

elements were focused: the potential system users,

the tasks to be performed, and the system

environment.

3.1.1 System Users

There are several considerations regarding a system

user, among which it can be mentioned: if the

application will be mono-user or multi-user; if the

users will stand at their place or remotely; and if the

users will be experts or novices, in terms of use of

virtual reality applications.

For the VE-Museum, the users were any people

interested to know the place. Therefore, the system

should be user-friendly to allow the user not to get

lost in the system actions. The actions and the

people's interactions were observed in the real

environment of the Museum, along with interviews

that were performed with employees and the

studying of the history of the city. The virtual

environment was built as a mono-user system.

The VE-Capoeira theme was selected by the

users, children and teenagers. Besides, as the

objective was to create a collaborative environment,

to work in a distributed platform, it was necessary to

identify types of avatars (virtual objects that

represent the users) representative of the theme and

also attractive to the users.

For the VE-Engineering, the users were students,

teachers, and engineering researchers, working in

projects for production of specific mechanical parts.

Given the specificity of the subject, it was identified

the need to train the users for an appropriate and

efficient use of the virtual environment.

In the three mentioned environments, the

requirements elicitation involved a meticulous

exploration and observation of the real environment.

For the VE-Museum, there were taken pictures and

measurements of the whole environment and of

objects that composed it; for the VE-Capoeira,

besides pictures, there were developed texts, films,

music, etc.; for the VE-Engineering, the

configuration and operation manuals were studied.

That explained the location of the objects in the real

world and also showed details of the floors, walls

and illumination, which would help the future

construction of the virtual environment objects.

3.1.2 System Tasks

In the requirements engineering phase, it is essential

to define the goals of the application, the necessary

tasks to reach those goals, and how the tasks will be

accomplished in the system.

For the VE-Museum, it was defined that it would

be a replica of the real museum. Therefore, it was

modeled with the higher level of realism possible.

The tasks that should be accomplished by the users

are to "walk" around the environment, visit the

rooms of the Museum, sign the visitors' book,

consult data regarding the collection of available

objects, etc. Those tasks should be performed

through a workstation, in a mono-user platform.

For the VE-Capoeira, the theme “Capoeira” was

chosen and approved by most of the users.

Consequently, it was necessary to identify the main

tasks that the users could accomplish, besides simply

to "walk" in the environment. For this, there were

identified and studied the main Capoeira poses that

would be implemented later through graphic

modeling and animation techniques.

For the VE-Engineering, the level of realism of

the Coordinate Measuring Machine was fundamental

so that the users could accomplish the foreseen tasks

of modeling the parts. It was also essential to

understand the correct operation of the machine,

including the complete domain of all movements

and the commands for triggering those movements.

3.1.3 Application Environment

The application environment can be defined by

several ways, as the physical environment, the

working environment and the social environment.

For virtual environments, the definition of the

physical environment in which the system will work

deserves special attention. It is important to

highlight that the physical environment can

represent the real environment with realism or create

an imaginary representation of the reality.

For the VE-Museum, the physical environment

constituted a replica of the museum, based on the

modeling of the rooms, the representation of the

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objects, and the drawing of the floor plan of the

building.

For the VE-Capoeira, there were identified

typical places of Capoeira games, as streets and

squares of Bahia, that were represented as sceneries

in the virtual environment.

For the VE-Engineering, it was created a scenery

representing a laboratory, not necessarily similar to

the real laboratory in which the machine was put.

3.2 Requirements Specification

3.2.1 General Functional Requirements

This specification aims to represent the requirements

by conceptual models (textual or in a graphic

notation) which describe the components and the

behavior of the intended software system.

The functional specification of the three

considered virtual environments were prepared in

Unified Modelling Language (Rational, 2006),

supported by the Rational Rose software (Fowler,

1997). Figure 4 shows a use case diagram prepared

for the VE Museum.

Figure 4: Use Case Diagram for the VE Museum.

3.2.2 Specific Functional Requirements

When a virtual environment is being developed, it is

important to consider three possible alternatives,

which interfere on the functional specification

(Stuart, 1996):

• Alternative 1. When the virtual environment

will reproduce tasks performed by users in a

real environment and the intention is to show

this situation the way it is.

• Alternative 2. When the users carry out

certain tasks in the real world, but the virtual

environment will reproduce such tasks

differently that they happen.

• Alternative 3. When the intended virtual

environment will comprise the

accomplishment of tasks and interactions that

are not carried out in the real world.

In the VE-Museum, there was observed the

occurrence of the three situations indicated above.

Through the elicitation process, there were verified

the tasks that should be accomplished in the same

way that the real environment, such as to walk in the

environment, open and close doors, turn on and turn

off lights, visualize pictures and objects, sign the

Visitors’ Book, etc. Besides, it was defined the

inclusion of some tasks in the virtual environment

that could not be executed in the real world, such as

to change rooms without moving through the floor

plan of the museum. In addition, other tasks of the

real environment were also executed in the virtual

world, but in a different way, such as to visualize

information through graphs placed in a walk-through

environment.

In the other two considered virtual environments,

there were also defined similar requirements to those

defined for the VE-Museum, for subsequent project

and implementation.

3.3 Nonfunctional Requirements

3.3.1 General Nonfunctional Requirements

Nonfunctional requirements are related to software

aspects, hardware characteristics or external factors,

which determine conditions or constraints to the

behavior of the intended system. Among these

requirements, it is important to point out the

following ones (Kirner, 1996; Sommerville, 1997):

• Performance. It is usually related to the

fulfillment of processing demands, response

time, resource utilization, throughput and

efficiency of system processes.

• Usability. It comprises the fulfillment of

criteria related to understanding and easiness

of use of the system and level of the user

satisfaction with the system.

• Security. It concerns the probability of the

system in defending itself from accidental or

intentional attacks, that can occur through

Guest

Interact

Interact with

the system

Visualize objects

Open/close door

Visualize graphics

Turn off/off

the light

Go to the visualization room

Give opinion about the

system

Visualize information

on the objects

Answer

extends

Start/stop music

extends

Select room

extends

Access the chat

extends

Walk

through the environment

CONTRIBUTION TO THE REQUIREMENTS ENGINEERING OF VIRTUAL ENVIRONMENTS

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improper access, denied use, and partial or

total destruction.

• Reliability. It is associated to the ability of

the system to behave in accordance with what

was previously specified, during a certain

period of time and with the foreseen

resources.

• Other requirements, as portability,

maintainability, accessibility, etc. (Kirner,

1996; Sommerville, 1997).

Virtual environments need to fulfill

nonfunctional requirements, which should be clearly

specified.

In the three focused virtual environments, special

attention was given to usability issues. The

increment of usability was seek, from the

requirements engineering phase, by the

identification of ways to make the navigation and

interaction easy and fast, such as: forecast of

previously defined routes to optimize the exploration

and walk-through in the environment; easiness of

alteration of view points by the user; inclusion of

explanatory texts; definition of clear metaphors;

identification of techniques and software for editing

images and modeling objects, aiming to build

graphic scenes that do not interfere on the system

response time to the user interactions.

The explanation of other nonfunctional

requirements, specified for the three considered

virtual environments, can be obtained in (Calonego,

2004; Kirner, 1999, Kirner, 2001).

3.3.2 Specific Nonfunctional Requirements

Besides the quality aspects stressed in the previous

sub-section, virtual environments have peculiarities

that demand the accomplishment of additional

nonfunctional requirements (Stuart, 1996; Vince,

2004). In this sense, it is expected that a virtual

environment can be:

• Synthetic. It means that the virtual

environment should be generated in real-time

by the computer system, which does not

happen with multimedia systems, in which

the presentations are previously recorded

before they are executed.

• Tri-dimensional. It means that the physical

environment that surrounds the user should

be modeled in three dimensions, and that the

user can walk around that environment.

• Multi-sensorial. It means that the

environment should include resources to

stimulate different human senses, as vision,

audition, touch, space sense, depth, etc.

• Immersive. It means that, besides visualizing

the scenes and hearing the sounds, the user

should have the impression that he/she is

really inside the virtual environment.

• Interactive. Such a requirement makes

possible the detection of stimulus sent by the

user and, instantly, the promotion of actions

capable to modify scenes and objects in the

virtual environment.

• Realistic. It refers to the level of precision

and conformity that the virtual environment

presents compared to the representation of

the real world.

• With presence. It is characterized by a

subjective sense that the user is physically

inside the virtual environment and, many

times, participating actively of this

environment.

4 REQUIREMENTS

EVALUATION

The objective of the evaluation is to assure that the

specification really represents the problem domain

and the user needs. It is important, in this phase, that

the stakeholders that participated in the previous

phases are also involved, so that it is possible to

make the validation and verification of the

requirements described (Castro, 1995).

A series of techniques exists for evaluation of the

quality of the requirements, including those that are

associated directly to virtual reality applications.

For the three considered virtual environments,

the requirements evaluation, in general, was

performed in an informal way, through consultations

to several people. Such approach of continuous

evaluation was facilitated because the systems had

been developed following a prototyping approach.

Among the three analyzed virtual environments,

the only one which was systematically evaluated

concerning its usability characteristics was the VE-

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Capoeira. For this, an heuristic evaluation was

performed, involving two usability specialists and

including the participation of students. This

evaluation identified some deficiencies, such as:

difficulty on operating some navigation commands;

use of technical language, in certain screens;

inadequate organization of graphic objects that

compose the user libraries.

Based on the evaluation results, a plan of

usability improvement for the VE-Capoeira was

prepared.

5 CONCLUSION

This work focused on requirements engineering, a

critical phase of software development, aiming to

contribute specifically for the elicitation,

specification and evaluation of virtual environments

requirements. The requirements engineering process

for virtual environments was outlined, taking into

account the concepts originating from the software

engineering, complemented by the experience

obtained through the development of three virtual

environments: VE-Museum, VE-Capoeira, and VE-

Engineering.

Several improvements would be necessary in the

considered virtual environments, mainly relating to

the evaluation of these systems.

The experience in the development of these

virtual environments made possible to identify a

series of needs, that could be fulfilled through the

investment in research related to topics as those

related as follow.

• Definition of taxonomies for the

categorization of virtual environments, that

could be adopted in studies of existing and

potential environments.

• Use of methods for elicitation, specification

and evaluation of requirements, that were

compatible with the peculiarities of the

different types of virtual environments. New

techniques and languages of specific purpose,

that could facilitate the identification and

representation of characteristics related to the

tri-dimensional representations (including

requirements of color, light, scale, point of

view, animation, etc.), would be very useful.

• Empirical studies for the investigation of

nonfunctional requirements for virtual

environments, with emphasis on usability

aspects, mainly those related to aspects of use

of browsers and special devices, as gloves,

glasses and head mounted displays.

• Empirical studies that investigate the

characteristics of potentials users of virtual

environments and behavior issues of these

users when using the environments.

Experience with virtual environments has

shown that people behave differently to the

interaction, navigation and immersion

propitiated by virtual reality applications.

New research will contribute to the progress of

the area, offering effective subsidies for the

professionals and final users involved in virtual

reality environments.

REFERENCES

Calonego Jr, N.; Kirner, C.; Kirner, T.G.; Abackerli, A.J.,

2004. Implementation of a virtual environment for

interacting with a numeric command machine. In

Proceedings of the 3rd IEEE VECIMS Int.

Conference, Boston, MA, USA, pp. 125-130.

Castro J.F.B., 1995. Introduction to Requirements

Engineering. Tutorial, JAI/SBC, Canela, RS, Brazil.

Fowler, M.; Scott, K., 1997. UML Distilled – Applying

the Standard Object Modeling Language. Addison-

Wesley, Reading, MA, USA.

Kim, G.J. et all., 1999. Software engineering of virtual

worlds. In Proceedings of the ACM VRST Symposium,

Taipei, Taiwan, pp. 131-138.

Kirner, T.G., Davis, A.M., 1996. Nonfunctional

requirements of real-time systems. In Advances in

Computers (Zelkowitz, M., Ed.). Volume 42,

Academic Press, pp. 1-37.

Kirner, T.G., Martins, V.F., 1999. A model of software

development process for virtual environments. In

Proceedings of the 2nd IEEE ASSET International

Symposium. Richardson, USA, pp. 155-161.

Kirner, T.G., Kirner, C., Kawamoto, A.L., Wazlawick,

R.S., 2001. Development of a collaborative virtual

environment for educational applications. In

Proceedings of the ACM WEB3D International

Conference, Paderborn, Germany, pp. 61-68.

Myers, B.A.; Hollan, J.; Cruz, I., 1996. Strategic directions

in human-computer interaction. ACM Computing Surveys, v.

28, n. 4, pp. 794-809.

Stuart, R., 1996. The Design of Virtual Environments.

McGraw-Hill, Fairfield, PA, USA.

Sommerville, I; Sawer, P., 1997. Requirements

Engineering: A Good Practice Guide. John Wiley &

Sons, England.

Vince, J., 2004. Introduction to Virtual Reality. Springer-

Verlag, Germany.

RATIONAL, 2006. UML. www.rational.com/uml.

CONTRIBUTION TO THE REQUIREMENTS ENGINEERING OF VIRTUAL ENVIRONMENTS

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