Database Model for Design Data

Iztok Savnik, Toma<=z Mohori<=c?, Tomi Dolenc, Franc Novak

Department of Computer Science, Jo<=zef Stefan Institute,

Jamova 39, 61111 Ljubljana, Slovenija,

?Faculty of Electrical Engineering and Computer Science,

University of Ljubljana, 61111 Ljubljana, Slovenija

Abstract

The paper presents a Construction Database Model (CDM) used for the conceptual level modelling of design objects. A primary intention of the CDM model is modelling hierarchically structured objects and construction dependencies among objects. CDM is an attribute based data model. The CDM model represents various abstractions identified in the semantic database models GSM, IFO, SAM* and FDM by means of attributes. To distinguish between different abstractions, the notion of attribute role is introduced. Special attention is paid to the representation of derived properties of the object. They are described by means of a constructor, that can be compared to derived attributes as defined in [10, 4, 22, 8]. The constructor enables the description and reevaluation of the design object construction process. The CDM is used as a data model for the storage system Cons-Base, designed for storing data in CAD applications.

1 Introduction

Design data encompasses data for describing entities modelled by the Computer Aided Design applications. Our work is concerned in particular with the designing of mechanical parts, their geometric representation, related technological data and tools for mechanical parts manufacturing. Hence, most examples in this paper will be drawn from geometric representations of mechanical parts.

Conventional data models are appropriate for representing large amount of the rigidly structured data usually stored in business applications, but they are not suitable for representation and manipulation of the design data. They do not provide constructs for representing hierarchically structured data, nor do

they provide constructs for derived data definition and manipulation. For this purpose, database models Cactis [10], Trait [4], IFO [2], GSM [11], FDM [22], SAM* [24], NF2 model [18], IQL [3] and 3DIS [9] are more suitable due to their capability of representing structural and behavioural information relating to the design object. These models are appropriate for describing entities in the software engineering environment [16], computer integrated manufacturing [24] and computer aided design [15, 18, 9].

In the paper the, Construction database model (CDM) is presented. The CDM is intended for conceptual level modelling and manipulation of design data. The primary focus of CDM is in the modelling of the design-object hierarchical structure and the construction dependencies between objects. CDM is intended for modelling data in the design and engineering application environment. It can be implemented as an extension of the commmercial database system or can be used as a data model integrated in the target application environment. The paper describes the structural part of the CDM data model, whereas the data definition and manipulation language interface is not the subject of this work. The language will follow the ideas of the languages DAPLEX [22], O2FQL [14], IQL [3] and FDL [17].

The CDM is an attribute based data model, therefore all object properties are described by attributes. The leading idea of the CDM model is representation of the various abstractions identified in the semantic database models GSM, IFO, NF 2, SAM* and FDM with attributes. To distinguish between different abstractions, the notion of attribute role is introduced. Attribute role divides attributes into different categories on the basis of the attribute meaning. Attributes can be of ordinary, structural, derived of implicit role, representing ordinary properties, hierarchi-