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id avocaad_2001_22
authors Jos van Leeuwen, Joran Jessurun
year 2001
title XML for Flexibility an Extensibility of Design Information Models
source AVOCAAD - ADDED VALUE OF COMPUTER AIDED ARCHITECTURAL DESIGN, Nys Koenraad, Provoost Tom, Verbeke Johan, Verleye Johan (Eds.), (2001) Hogeschool voor Wetenschap en Kunst - Departement Architectuur Sint-Lucas, Campus Brussel, ISBN 80-76101-05-1
summary The VR-DIS research programme aims at the development of a Virtual Reality Design Information System. This is a design and decision support system for collaborative design that provides a VR interface for the interaction with both the geometric representation of a design and the non-geometric information concerning the design throughout the design process. The major part of the research programme focuses on early stages of design. The programme is carried out by a large number of researchers from a variety of disciplines in the domain of construction and architecture, including architectural design, building physics, structural design, construction management, etc.Management of design information is at the core of this design and decision support system. Much effort in the development of the system has been and still is dedicated to the underlying theory for information management and its implementation in an Application Programming Interface (API) that the various modules of the system use. The theory is based on a so-called Feature-based modelling approach and is described in the PhD thesis by [first author, 1999] and in [first author et al., 2000a]. This information modelling approach provides three major capabilities: (1) it allows for extensibility of conceptual schemas, which is used to enable a designer to define new typologies to model with; (2) it supports sharing of conceptual schemas, called type-libraries; and (3) it provides a high level of flexibility that offers the designer the opportunity to easily reuse design information and to model information constructs that are not foreseen in any existing typologies. The latter aspect involves the capability to expand information entities in a model with relationships and properties that are not typologically defined but applicable to a particular design situation only; this helps the designer to represent the actual design concepts more accurately.The functional design of the information modelling system is based on a three-layered framework. In the bottom layer, the actual design data is stored in so-called Feature Instances. The middle layer defines the typologies of these instances in so-called Feature Types. The top layer is called the meta-layer because it provides the class definitions for both the Types layer and the Instances layer; both Feature Types and Feature Instances are objects of the classes defined in the top layer. This top layer ensures that types can be defined on the fly and that instances can be created from these types, as well as expanded with non-typological properties and relationships while still conforming to the information structures laid out in the meta-layer.The VR-DIS system consists of a growing number of modules for different kinds of functionality in relation with the design task. These modules access the design information through the API that implements the meta-layer of the framework. This API has previously been implemented using an Object-Oriented Database (OODB), but this implementation had a number of disadvantages. The dependency of the OODB, a commercial software library, was considered the most problematic. Not only are licenses of the OODB library rather expensive, also the fact that this library is not common technology that can easily be shared among a wide range of applications, including existing applications, reduces its suitability for a system with the aforementioned specifications. In addition, the OODB approach required a relatively large effort to implement the desired functionality. It lacked adequate support to generate unique identifications for worldwide information sources that were understandable for human interpretation. This strongly limited the capabilities of the system to share conceptual schemas.The approach that is currently being implemented for the core of the VR-DIS system is based on eXtensible Markup Language (XML). Rather than implementing the meta-layer of the framework into classes of Feature Types and Feature Instances, this level of meta-definitions is provided in a document type definition (DTD). The DTD is complemented with a set of rules that are implemented into a parser API, based on the Document Object Model (DOM). The advantages of the XML approach for the modelling framework are immediate. Type-libraries distributed through Internet are now supported through the mechanisms of namespaces and XLink. The implementation of the API is no longer dependent of a particular database system. This provides much more flexibility in the implementation of the various modules of the VR-DIS system. Being based on the (supposed to become) standard of XML the implementation is much more versatile in its future usage, specifically in a distributed, Internet-based environment.These immediate advantages of the XML approach opened the door to a wide range of applications that are and will be developed on top of the VR-DIS core. Examples of these are the VR-based 3D sketching module [VR-DIS ref., 2000]; the VR-based information-modelling tool that allows the management and manipulation of information models for design in a VR environment [VR-DIS ref., 2000]; and a design-knowledge capturing module that is now under development [first author et al., 2000a and 2000b]. The latter module aims to assist the designer in the recognition and utilisation of existing and new typologies in a design situation. The replacement of the OODB implementation of the API by the XML implementation enables these modules to use distributed Feature databases through Internet, without many changes to their own code, and without the loss of the flexibility and extensibility of conceptual schemas that are implemented as part of the API. Research in the near future will result in Internet-based applications that support designers in the utilisation of distributed libraries of product-information, design-knowledge, case-bases, etc.The paper roughly follows the outline of the abstract, starting with an introduction to the VR-DIS project, its objectives, and the developed theory of the Feature-modelling framework that forms the core of it. It briefly discusses the necessity of schema evolution, flexibility and extensibility of conceptual schemas, and how these capabilities have been addressed in the framework. The major part of the paper describes how the previously mentioned aspects of the framework are implemented in the XML-based approach, providing details on the so-called meta-layer, its definition in the DTD, and the parser rules that complement it. The impact of the XML approach on the functionality of the VR-DIS modules and the system as a whole is demonstrated by a discussion of these modules and scenarios of their usage for design tasks. The paper is concluded with an overview of future work on the sharing of Internet-based design information and design knowledge.
series AVOCAAD
references Content-type: text/plain
last changed 2005/09/09 08:48
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