||This paper presents the results of some studies of datamodeling and layering practice carried out for the draftBritish Standard 'Construction Drawing Practice - Guide f o rgraphic representation by computer'. This standard, BS 1192Part 5, is currently a draft on which public comments havebeen received but which will not be final until 1989. Itsobjectives are to complement developing international dataexchange standards by guiding those designing buildings withCAD to organize data so that its structure can betransferred. It has three main elements:1. Translation of system terminology into standard terms.2. A simple representation of data structures.3 . Guidance on allocating building data to layers.In the first study six of the systems most widely used inthe UK were represented in IDEF IX data modeling format toshow their similarities and differences, and the standardincludes a simplified data structure which can be related toeach of these. Typical variations are identified andsystem terminology is related to standard terms proposed.The second study looked at current practice in allocatinglayers or categories, both by FEDCAD in user groups and byCICA in individual members using CAD. A number of criteriafor classifying layers were found and these included, inorder of frequency:1. Job specific elements.2. Elements of drawings, eg. grids, text.3 . Elements of buildings, eg. phases, floors, services.4 . Standard element systems, eg. CI/SfB.5. Types of drawing eg. plans, elevations, perspectives.The recommendations of the standard are that a common systemshould be used allowing flexibility in the numbers oflayers. CI/SfB Table 1 and the Common Arrangement are seenas suitable systems appropriate to different stages of thedesign process.