The Engineering Department of ICI PLC has developed an interactive graphical system for the design of Ioadbearing steel structures. The system is believed to be unique. Steel- work is designed in the system to BS 449 utilizing a series of design programs, a sophisticated database (specifically tailored to steelwork requirements) and graphical techniques. The system gives the Engineer the ability to make considerable savings in effort and amounts of steelwork. The system interfaces to the PDMS* modelling system, DOGS draughting package and frame analysis programs. The paper describes the development of the system and its use in the Engineering Department, ICI. D Button is a Civil Project Engineer in the Engineering Department, ICI. He is at present responsible for computer aids for the Civil Engineering Group and in particular for the development of ISOSTEEL. Flexibility in CAPP through system design S Evans and P J Sackett (University of Bath, UK) Computer Aided Process Planning (CAPP) is the major link between CAD and CAM. The desirability of a truly integrated CADCAM system, and the benefits claimed for CAPP are at odds with the speed of adoption of CAPP systems by industry. The inability of currently available systems to cope with a wide product and process range is primarily responsible for this position. This paper describes the design and operation of a CAPP system which places a premium on flexibility without cost penalty. The resul- tant system is applicable to a wide variety of process planning environments. Stephen Evans is currently completing his PhD thesis in Computer-Aided Process Planning. Previously he gained a BSc (Hans) in Mechanical Engineering at the University of Bath whilst completing an engineering apprenticeship at Marconi Radar Systems Ltd. Dr Peter Sackett is a Lecturer in Manufac- turing Systems at the University of Bath. He holds a PhD and MSc from UMIST. He is currently researching on a number of areas in computer integrated manufacturing systems. Commercial piping CAD databases W G Beazley (CA DDS Operations, Brown & Root, TX, USA) Many commercial CAD piping databases are now available for piping design. Certain compromises were made to achieve a com- mercially useful product. This paper reviews selected commercial implementations of the theoretical needs of piping databases. Four classes of software are discussed: • fast drafting software • mapping derived software • mechanical/electrical derived software • database management system (DBMS) derived software Based on the author's experience and know- ledge of each class of CAD software, a rating for several possible operational CAD environ- ments is developed from piping database needs. SOLID MODELLING 2 Creating large solid models for NC toolpath verification J A Woodwark and A F Wallis (University of Bath, UK) Toolpath verification is a natural application of solid modelling. However, the large amount of data that must be handled renders many existing techniques unsuitable. This paper shows how the authors' spatially segmented set-theoretic structure copes with this complexity. Developments in control- ling the spatial division process are outlined. These have been a major feature of the tool- path verification work but are also important to the development of this type of modelling system in general. A F Wallis is a Research Assistant at Bath University. He has just completed three years postgraduate research on solid model- ling systems. J R Woodwark is a Lecturer in Manufac- turing at Bath University. His research interests are in computer aided engineering, especially computer-based shape represen- tation and robotics. An introduction to relational topology P Hanrahan (Computer Graphics Laboratory, New Yorh Institute of Technology, NY, USA) It is often convenient to separate the repre- sentation of spatial models into two com- ponents: a topological component that contains connections between different parts and a geometric component that holds the parts' positions and shapes. This separa- tion is useful since independent constraints exist that can be applied in each of these domains to enforce the notions associated with well-formed shapes. In this paper a new method of represent- ing topological information in 1D, 2D and 3D is presented based on an ordered- adjacency relation amongst the different topological elements. This relation follows naturally from considerations of adjacency, ordering and valency. Constraints are then derived which guarantee that models stored in the database are well-formed, that is, are orientable closed manifolds. These con- straints and other representation indepen- dent properties can be expressed using relational algebra. Pat Hanrahan is a research programmer with the Computer Graphics Laboratory at New York Institute of Technology. His primary research interests are in computer animation, geometric modelling and image synthesis. Mr Hanrahan received his BS degree in Nuclear Engineering from the University of Wisconsin and is currently working on his doctorate in Biophysics. A new method of view synthesis for solid modelling W L Chung (,4 utomatlon Systems Labora- tory, Korea A dvanced Institute of Science and Technology, Korea) A novel method of view synthesis for geometric modellers based on constructive solid geometry is described. The new method transforms the problem of 3D solid composition and visibility computation into that of 2D planar contours consisting of line and conic edges ('conical polygons') that are obtained by cutting quadric volume primi- tives with parallel scan planes and that of planar ray combines operated on conical polygons. It is highly efficient due to syste- matic reduction of dimenslonality and geometric complexity of objects and processes involved and due to the full exploitation of natural properties of quadrics and coherence of scan line algorithms. Won L Chung holds a PhD in computer science from University of Illinois and is Associate Professor in charge of Automation Systems Laboratory at KAIST with CADCAM/ClM and CBE as research areas. Synthesis of volume modelling and sculptured surfaces in BUILD G E M Jared (University of Cambridge, UK) and T Varady (Hungarian Academy of Sciences) EXPERTSYSTEMS1 An extended expert system for display management in a CADD system J H Boose (,4 rtlflclal Intelligence Center, Boeing Computer Servlces, WA, USA) This paper describes a prototype extended expert system, AIDER, which was built to handle the display environment on a CADD package known as AIDS, the Architectural Interactive Design System. It performs by monitoring the flow of information between the user and the various parts of the system. By setting up spontaneous computations (a type of demon) to watch communications between the user, the applications modules, and the data base, AIDER sets current context filters which modify this information with respect to numerical and graphical precision, and the level of detail needed. Data can be created, modified, deleted or delayed. Context filters can be created, modified, deleted, and invoked. John Boose received a Bachelor of Architec- ture degree from the University of Maryland in 1977, performed graduate work at MIT's Architecture Machine, and is currently employed at the Artificial Intelligence Center of Boeing Computer Services in Seattle, WA, USA. The place of expert systems in architecture John S Gero and Richard Coyne (Computer Applications Research Unit, Department of volume 16 number 2 march 1984 109