OBJECT-ORIENTED MODELLING USING XML IN COMPUTER-
AIDED ARCHITECTURAL AND EDUCATIONAL CAD
The Problem of Interoperability exemplified in two Case Studies
T. FISCHER, M. BURRY*, ROBERT WOODBURY**
Fachbereich Erziehungs- und Humanwissenschaften
University of Kassel (GhK), Germany
*School of Architecture and Building
Deakin University, Australia
tfischer@hrz.uni-kassel.de, mburry@deakin.edu.au
**School of Architecture, Landscape Architecture and Urban Design
University of Adelaide, Australia
rw@arch.adelaide.edu.au
Abstract. This paper highlights our application of XML as a messaging and storage
format for parametric 3D modelling and pattern-oriented online teaching. As a recent
format for data description and transport technology XML is designed to allow
communication between arbitrary data platforms - and to communicate purpose-
insensitively. We have used it to communicate design patterns as well as design
parameters and as a consequence experienced a remarkable technical similarity between
both approaches with their common manifestation in object orientation. There is a
necessity to perform dynamic synchronizations of semantics between ‘knowledge
domains’ involved in design processes in order to provide the necessary conceptual
openness. At this time, this requirement appears to be alien to available XML schema
specifications and tools.
1. Introduction
Data modelling in computer-aided design contexts requires re-modelling of real
world sections to the same extent that its product relates to problems of the
natural world (this is typically the case). In architecture an example is part of a
building or a construction process; in teaching a class of students and the design
of the learning progress. As neither the design processes themselves nor the
applications of their outcomes happen in isolation, we experience a significant
demand for interoperable data formats in order to exchange digitally modelled
reality and to run trivial subtasks automatically. In the field of architecture as

146 T. FISCHER, M. BURRY AND R. WOODBURY
well as in the field of education, XML specification initiatives have developed
data formats which are intended to cater for this purpose (aecXML and IMS
XML metadata schemas). Working on two research projects, one related to
architectural 3D-modelling and one to architectural online education, we have
had to face the reality of real-time cross-domain data modelling with the
conclusion that the XML specifications mentioned above suffer from a
conceptual deficit. In this paper we discuss the progress made with both
projects from a technical standpoint and report on the findings we gained
regarding data modelling strategies.
2. The Paramorph
Intended as a rejection and an alternative to accident-oriented computer-based
design methodologies, the paramorph is a numerical/geometrical engine
connected to a 3D-Renderer which allows the controlled generation of highly
variant 3D geometry through so-called ‘parametric design’, or ‘associated
geometry’. At the beginning of a design process, the paramorph in its initial
state is a description of a potential geometry without real manifestation, or a
‘pattern’. To produce such a manifestation the designer has to provide a finite
number of parameters that are applied to the pattern. The mathematical
description of the associative geometry is sufficient to assign defined attributes
to any element of the model. Basic geometrical properties are initially defined
constants; morphological variations are the results of controlled manipulations
to the parameter values.. In contrast to the freedom the designer experiences
sculpting a ‘blob’ in a click-and-drag 3D modeller, the paramorph allows a
structured design process that is easily repeated, that is, the results of
experimentation are reproducible. Parametric design, as with other design
methods, aims to limit the problems that come along with totally free design
situations – but potentially at the cost of their freedom. Although this cost does
not remain unchallenged (Miller: 1990) parametric design nevertheless offers
considerable benefits to the architectural user: the initial pattern itself can be
regarded as a variable, as a replaceable pattern or object(Burry: 1996). Pattern
descriptions can be communicated between designers and platforms. They
might be developed by expert designers and used by non-experts with the
expertise captured within their description becoming reusable expert-knowledge.
The distinction between geometry designer and educational-tool designer
becomes blurred. Moreover, parametric design provides a means to design
buildable virtual architecture, as it were: a central problem of building
hypersurfaced architecture is the transfer of Cartesian information from drawing
or model-space into natural space. Some geometries, however, are more likely
to be transferable than others such as ruled surfaces. As the principle topology
of a paramorph pattern is its persistent property and not affected by given