J. H. Sims Williams

Features aka the semantics of a formal language of manufacturing

Features are application and viewer-dependent interpretations of geometry. This article demonstrates how the notion of features arising out of geometric data may be formalised as the semantics of a language of shape, using machining operations as an extended example. The syntax and semantics of formal languages are discussed, with particular reference to their use in design. A simplified lathe is defined, and a parametric attributed set grammar is presented which specifies the range of shapes manufacturable on that lathe. A simple feature space is then defined, in which feature models representing those shapes may be constructed. The link between the shapes and the feature models is then formalised as the semantics of the grammar using description functions, and it is shown how the feature models develop as shape generation proceeds. Finally, some implications of this work for feature-based design and manufacturing are discussed.

Describing process plans as the formal semantics of a language of shape

A method of formalising manufacturing information for use in the design process is presented. The method uses a grammar of shape and its formal semantics to describe the set of objects manufacturable by a given process, to generate objects from that set, and to describe corresponding process plans for the manufacture of those objects. The grammar thus defines a search space for generative process planning, and the semantics provide an interpretation of the results of a search in that space.

Review: An Information Management System for Informal Design Data

Engineering information management may be divided into formal information management, which involves data modelling, data exchange and transaction handling, and informal information management, which is concerned with the organisation and delivery of design advice and design parameter data. This paper describes a system, called Review, which has been developed for the management of informal design information from multiple sources. The system uses a hybrid hypertext/database approach to provide for the indexing and viewing of information sources using arbitrary attribute sets, and for the establishment of relationships between information entities using both static and dynamic links in a hypertext framework. Information may be accessed both by query and by browsing along relationships in the hypertext network. The paper presents an overview of the system design, and examples of its application to design advisory systems and documentation.

Observations on the application and development of parametric-programming techniques

Abstract A parametric program may use rules and algorithms to define the relationships between dimensions and elements of designs, and it may thus generate variants of a design. Programs currently in use have technical limitations in their ability to handle time-varying and imprecise data, the search for suitable existing designs and their maintainability. The paper suggests how these and other limitations can be overcome to widen the field of application of parametric programs.

Grammars of Features in Design

A method of specifying and generating a set of designed objects known to be assessable is proposed. It is suggested that by generating designs which can be quickly assessed, and through being supplied with advice and assessment as the design proceeds, the designer can improve the design to product cycle. The method is based upon attributed graph grammars which specify valid manipulations of feature models in feature-based design. Semantic functions compute and constrain the feature attributes, and generate a simultaneous assessment as the design progresses. Finally, an example within the domain of stress concentration prediction is presented.

Conceptual geometric reasoning by the manipulation of models based on prototypes

The ability to understand the implications of the geometry of solid objects is an important aspect of intelligent behavior. This paper presents work designed to enable reasoning with relatively loose conceptualizations of geometry. The method operates by comparing target geometry to known geometry, and involves the manipulation of models based upon prototypes. In particular, three techniques of simplification, approximation, and transformation are discussed. Finally, an application of the method to the domain of stress concentration prediction is presented.

Constraint Unification Grammars: Specifying Languages of Parametric Designs

A grammar formalism for generating parametric objects is presented. The objects have differing topologies, complete with constraints which, when satisfied, ensure that design specifications are met. The representation is based on recursively-defined structures of attributes, values and constraint expressions. In the rewrite operations of the grammar, pattern matching is replaced by constraint structure unification, which preserves and combines constraint expressions. The generated objects consist of structures with declarative constraints ranging over the complete parse tree for the generation. A grammar specifying a simple mechanical design problem is discussed, followed by an example generation of an object in the language.

Reasoning with geometry: Predicting stress concentration factors

Abstract Fundamental to any AI-based design and analysis tool will be an understanding of geometrical form and function. This paper describes some current research into representing automotive components, and reasoning about such representations in the domain of stress concentration analysis. The process of predicting stress concentration is described and identified as a suitable subject for knowledge-based geometrical reasoning. A broadly feature-based representation is derived which attempts to model the conceptual representation maintained by an analyst. Object-oriented and rule-based methodologies are applied to this representation, and two different approaches in the content and style of the representation are highlighted. Some examples of the reasoning process applied to the representation are presented, which demonstrate the effectiveness of this technique in its ability to manipulate and simplify geometrical descriptions, based on an understanding of their significance in engineering terms.