TAKING ADVANTAGE OF THE MARKUP LANGUAGE APPROACH IN DESIGNING
VIRTUAL COLLABORATIVE ENGINEERING ENVIRONMENTS
Jorge Alberto Campos1
jorge@unifacs.br
Cesar Teixeira1
cesar@unifacs.br
Maria da Graça Pimentel2
mgp@icmc.sc.usp.br
Cláudio da Costa Pinto1
claudio@unifacs.br
UNIFACS - Universidade Salvador, Salvador, Brazil.
2
USP - Universidade de São Paulo, Brazil.
ABSTRACT
This paper discusses how the combination of the
technologies
for
representing
three-dimensional
information in virtual reality and for representing
structured documents may bring synergetic results in the
development of collaborative projects in the areas of
Engineering and Architecture. It is presented a generic
and extensible solution for associating context-based
information to the elements defined in the Virtual Reality
Modeling Language (VRML). Such solution exploits the
open model for defining structured documents proposed
by the World Wide Web Consortium (W3C).
Keywords: XML, VRML, RDF, Metadata,
Virtual Reality, Virtual Engineering,
Collaborative Projects.
1.INTRODUCTION
Communities in several areas of the knowledge have
created specific languages to express ideas or phenomena
relevant to their work. These languages are often
composed of symbols and special characters and usually
are well understood only by the elements within the
communities itself, mainly due to the fact that no
semantic is defined by the language.
The Architecture/Engineering/Construction Industry
(AEC) has developed a language to represent objects
dealt with in their projects. The language uses twodimensional symbols for representing three-dimensional
elements in the real world. The use of two-dimensional
symbols is imposed by the medium where the projects
are usually presented: paper and, later, computer screens.
However, such language is not an accepted standard even
among the AEC community. It is not unusual architects
and engineers using the same symbol for representing
different objects, for example.
The provision of three-dimensional computer models in
virtual reality has introduced a new metaphor in the
development and representation of Engineering and
Architecture projects, allowing a real visualization of the
elements being designed[2]. Although these models use a
real, less symbolic representation, the integration with
some symbolic notation is still necessary in order to
allow the designer to properly identify some elements.
An example is the use of colors to represent the different
kinds of tubes that may be necessary in a building, such
as associating the color green with water and black with
inflammable fluids. Notations like these are strongly
dependent of the user’s interpretation, and as such it is
difficult to be integrated in applications where the
information must be machine processed.
A similar dependency on the user's interpretation occurs
with most documents in the World Wide Web (Web) so
far: those documents that use HTML as specification
language use a restrict group of tags associated to the
presentation form of the document. As a result, any
structural or semantic information produced by the
author may be processed only by reader user. As an
illustration, consider the example of information such as
Project Name, Project Description, Author's name or
Author's email, contained in most projects, that, in order
to be presented in a HTML document, are likely to be
formatted using the same generic presentation elements
associated to paragraphs.
The main claim in this paper is that two of the
technologies in increasing use in the Web, that for
representing virtual three-dimensional worlds and that
allowing the formal definition of structured documents, if
used together, can promote the development of
collaborative work in engineering and architecture
design. The definition of a specific language should
result from the integrated work from interested
communities, such as manufactures, clients and
engineers. The Computer Science community is to be in
charge of the provision for applications associated with
the authoring, interchange and visualization of the
information.
The remaining of this paper is organized as follows. The
next sections discuss the main technologies used in the
visualization of three-dimensional information and in the
definition of structured documents in the Web. Next, a
proposal for the definition of structured elements
associated with computational models of virtual reality is
presented, followed by an example of its implementation,
in order to demonstrate how the two technologies can be
used to promote the development of collaborative work
in engineering and architecture design. The paper
concludes discussing related and future work.
the engineer wants to simulate two scenarios: first
considering the cold and hot water tubes in separate, and
then considering them simultaneously, he or she would
have to request the server machine to deliver a new
version in virtual reality for each of the desired
possibilities.
As illustrated in Figure 1, these requests could be
implemented, for example, through the submission of
HTML forms or by means of direct access to the
database in the server, using the Common Gateway
Interface (CGI)[4].
DB
DB
VRML
Converter
Application
CGI
2. THE CURRENT 3D VISUALIZATION
PARADIGM ON THE WEB
The Virtual Reality Modeling Language (VRML97) [7]
is an ISO standard for the representation of threedimensional information in the Internet.
VRML is a descriptive language for virtual worlds in
which a door, a window, a tube or any other object in the
virtual environment corresponds to group of nodes
having associated geometry, appearance and position in
space. As a result, the real meaning of each object is
known only by the application that generated its
representation in virtual reality, since the language does
not support the association of semantic information to the
elements that represent the virtual environment.
A program in VRML defines a series of nodes, or
building blocks, that allow the representation of a virtual
environment. Once defined such a virtual environment in
VRML, a user is able to visualize and interact with the
environment, as well as to navigate through the virtual
objects and to activate hyperlinks to other documents or
virtual environments.
As an motivation, consider the scenario where an
engineer is analyzing the interference the tubes for hot
and cold water could have in the structural elements of a
building. Suppose that the necessary information is
stored in a server machine available over the Internet. If
HTML
VRML
Server
Client
Visualization Application
Figure 1 – Visualization through the Common
Gateway Interface (CGI)
The approach illustrated in Figure 1 presents many
inconveniences. First, it depends strongly on the
existence of enough resources in the server to allow the
simultaneous attendance of several requests of engineers,
working, eventually, in different projects around the
world. Second, it demands an application that must be
able to access all the involved databases, which are likely
to be non-uniform and distributed (indicated by the
dashed oval in the figure). Third, it generates an intense
traffic of information between the server and the client
machines. Last, but not least, it does not exploit the
computational capabilities of the client machine which
are used only for presentation purposes.
An alternative approach, illustrared in Figure 2,
corresponds to the situation where the server, upon
demand of a client, extracts from the databases
containing the raw data of the computational models for
the information requested and repass them in their
original format to the client machine.
additional effort to support plug-in applications for all
client machines. Last, but not least, the substituition of a
computational model or the definition of a new data
format demand great effort in updating the application
both at client and server sides.
3. THE CURRENT STRUCTURED DOCUMENTS
PARADIGM ON THE WEB
DB
DB
Application
Server
Client
DB
DB
VRML
Converter
Visualization Application
Figure 2 – Visualization through Plug-ins
As a result of this approach, a subset of the information
contained in the database is sent to the client. In the
client machine, an application would be in charge of
converting the original data to VRML as well as of
supporting some local simulation without the need to
frequent additional requests to the server. Such an
application could be implemented, for instance, as a
plug-in associated to the original HTML browser.
The World Wide Web Consortium has proposed the
eXtensible Markup Language (XML)[1,8] as a language
which allows communities and applications to define
their own set of structured elements to be exchanged and
presented in the WWW. XML is a subset of Standard
Generalized Markup Language (SGML) [3], an ISO
standard for the formal specification of the structure of
electronic documents.
The extensibility nature of XML allows its use in
different applications: in the representation of documents
of specific areas such as Mathematics (MathML) [8], in
the coding of Metadata (RDF) [5], in the specification of
the synchronization of streamed multimedia (SMIL) [10],
among others. It is out the scope of this paper a
discussion of the many specifications already under
development. The World Wide Web Consortium [6]
provides appropriate references.
In this context, the Resource Description Framework
(RDF) [5] is an XML application that formalizes the
definition of the mechanisms for the representation of
Metadata, in order to allow interoperability among
applications exchanging machine understandable
information on the Web. The basic idea of RDF is not to
define a universal set of Metadata, but to provide the
necessary mechanisms so that the several communities
may code, interchange and reuse structured Metadata.
As an example, consider the following declaration
contained in a document:
Leonardo
DaVinci's
davinci@artists.art
e-mail
is
Consider again the scenario where an engineer analyzes
the interference that the tubes for hot and cold water
could have in the structural elements of a building. When
using the approach in Figure 2, the engineer could
request all the data referring to tubes and structural
elements in a particular building and, running simulations
in the client machine, generate the visualizations for the
combinations under investigation.
Although this declaration is perfectly understandable for
a human, it is very unlikely that a machine will properly
process it with ease. The RDF data model consists in the
definition of a triple of resource, property-type and value
that allows meaning to be associated to a declaration, so
that it that can be read and understood both for human
and machines. The meaning of each component in this
triple is as follows:
This approach reduces the traffic between client and
sever machines at the same time that exploits the
processing capabilities of the client machine. However,
the approach is still highly dependent on the data format
enforced by the original models; moreover, it implies an
Resource: anything described by a declaration RDF
Property-Type: the characteristic or attribute type
used to describe the resource
Value: the value associated to the resource
Graphically, the relationship established by the triple can
be represented by a graph, as presented in Figure 3:
Leonardo
DaVinci
e:mail
davinci@
artists.art
Figure 3 – Graphic representation of the a RDF triple
This approach, illustrated in Figure 4, provides for the
uniform treatment of the information in the several
databases of the many areas which may be involved in
the project. It means that the elements of virtual reality,
as well as their meaning, may be defined by the AEC
community in an uniform way. Other advantage of the
present proposal is the potential reduction in the traffic of
information in the network and in the number of requests
to the server during the simulations made by the
designer, at the same time that it exploits the processing
capabilities of the client machine.
In XML-RDF, this declaration could be written as
follows:
<RDF:RDF>
<RDF:Description about="Leonardo DaVinci">
<RDF:E-mail>davinci@artist.art</RDF:E-mail>
</RDF:Description>
</RDF:RDF>
DB
The prefix RDF: is a resource of the language XML
called namespace that allows the unambiguous
identification of the meaning and values of the elements
they specify. The element RDF itself is used in the
declaration of Metadata within an XML document. The
meaning and values of the elements Description and
E-mail are described in the vocabulary associated to
the prefix.
Application
XML
Converter
Server
XML Interpreter
A document XML containing the declaration above
would have two other lines in its beginning, such as in:
<?xml version = “1.0”?>
<?xml:namespace
ns=xmlns:rdf=http://www.w3c.org/rdf/schema
prefix=RDF >
<RDF:RDF>
<RDF:Description about="Leonardo DaVinci">
<RDF:E-mail>davinci@artist.art</RDF:E-mail>
</RDF:Description>
</RDF:RDF>
The first line identifies the document as compliant the the
1.0 version of XML. The second line identifies the
location of the vocabulary that defines the elements with
the prefix “RDF:”.
4.
PROPOSAL
This work proposes the incorporation of meaning to the
elements of virtual reality documents built in VRML,
using the syntax XML-RDF, in order to facilitate and
promote the development of collaborative engineering
projects over the Internet. The incorporation of meaning,
or semantics, to the elements of virtual reality would
allow an application to set up and to processes a VRML
file locally, based on the data supplied by the designer
and in the semantics of each element.
DB
Client
Visualization Application
Figure 4 - Visualization through XML-RDF.
Under this proposal, let us consider again the scenario
where an engineer analyzes the interference the tubes for
hot and cold water may have in the structural elements of
a building. The engineer could access the XML-RDF
information, necessary to build the virtual environments,
from different databases and developed under distinct
applications by other designers. Such information could
be stored in many servers worldwide. This would
demand that an application in the client machine would
allow the engineer to define the restrictions to be applied
and to request the data necessary for the virtual reality
simulation to run locally. Moreover, the engineer would
be able to request modifications to be made in the current
visualization, which would be processed in the client
machine with no need for accessing the remote servers.
5.
IMPLEMENTATION ASPECTS
In order to illustrate implementation issues, this session
presents the representation of a red cube in VRML and
the corresponding XML-RDF representation, as
proposed in this paper. This simple example
demonstrates the immense potential of the introduction of
semantics to the elements of a virtual world. Moreover, it
is important to note that the observations regarding this
example can be easily extended for any application that
uses this metaphor.
A VRML document that represents a cube of dimension
1 unit is shown below:
#VRML V2.0 utf8
Transform {
translation 0 1 0
children Shape {
appearance Appearance {
material Material {
diffuseColor 1 0 0
}
}
geometry Box {
size 1.0 1.0 1.0
}
}
}
The representation of the same cube in XML-RDF could
be as follows:
<?xml version="1.0"?>
<?xml:namespace
ns=xmlns:rdf=http://www.w3c.org/rdf/schema
prefix=RDF>
<?xml:namespace
ns=xmlns:vrml=http://www.vrml.org/rdf/schema
prefix=VRML>
<?xml:namespace
ns=xmlns:aec=http://www.aec.org/rdf/schema
prefix=AEC>
<RDF:RDF>
<RDF:Author>Jorge Campos</RDF:Author>
<RDF:Organization>Unifacs</RDF:Organization>
<AEC:Revision_Number>01</AEC:Revision_Number>
<AEC:Revision_Date>1999-01-12
</AEC:Revision_Date>
<AEC:Unit>Meter</AEC:Unit>
<VRML:Header Header=”#VRML V2.0 utf8”>
<VRML:Transform>
<VRML:translation>
0 1 0
</VRML:translation>
<VRML:children>
<VRML:Shape>
<VRML:appearance
name=My_Appearance>
<VRML:material
name=My_Material>
<VRML:diffuseColor
value=1 0 0/>
</VRML:material>
</VRML:appearance>
<VRML:geometry>
<VRML:Box>
<VRML:Size
Value=1.0 1.0 1.0/>
</VRML:Box>
</VRML:geometry>
</VRML:Shape>
</VRML:children>
</VRML:Transform>
</VRML:Header>
</RDF:RDF>
The vocabulary presented in this example is fictitious and
suggests the entities that could take the responsibility for
their definition. It seems natural that the W3C would
define the most generic elements so that they can be used
potentially by any community. It would be left to the
consortium of the VRML language the definition and
maintenance of the specifications with all the existent
elements in the language and its possible values. The
AEC community would be in charge of the definition of
the elements that are specific to its area and that would
be used to introduce semantics to the objects modeled in
virtual reality.
The application in charge of interpreting and presenting
the VRML document would use the elements defined by
the AEC community to identify, in the document, the
VRML elements that satisfy the restrictions established
by the engineer or designer. For example, the engineer
could request the application to show the elements from
the original or from the latest version of a project.
Another example would be the partial presentation of the
project features, only those ones suggested by a specific
designer.
6.
EXPANSIBILTY
The proposed approach can be naturally integrated with
other facilities already available in the Web. For
instance, applications can extract information from the
navigation through a given project to produce a slide
show, and as such using the results from the VRML
processing to generate a SMIL [10] document.
7.
CONCLUSION AND FUTURE WORK
The creation of mechanisms for incorporating semantics
to objects dealt by virtual reality applications promotes
the development of collaborative projects in the
engineering and architecture domains over the Internet.
The joint use of standard mechanisms for the
representation of objects, used both by virtual reality and
structured documents applications, results in an open and
expandable solution. The implementation of an
application capable of processing the documents that use
the syntax of the XML-RDF language combined with the
objects from VRML specifications is not only possible
but also likely to be very relevant.
In order to demonstrate the potential of the present
proposal, it is under specification a model of document in
XML-RDF, and under development an application that
processes such a document in order to present it in a Web
browser.
It is an important point that the proposal presented here is
generic, so that it can be used by any community having
the three-dimensional representation as a main
communication media
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http://www.w3.org/TR/1998/REC-xml199980210.html
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URL:http://www.w3.org
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