The object-oriented paradigm has a number of widely recognised strengths when applied to data management, but the increased complexity of actual systems compared with their relational predecessors often means that such databases are less readily accessible to nonprogrammers than relational systems. A number of proposals have been made for textual, form-based and graph-based query interfaces to object-oriented databases, but it is clear that a single approach cannot be considered to be the best, given the wide range of potential user groups, application domains and tasks. The paper presents a query interface to an object-oriented database which supports alternative user-level query paradigms in a fully integrated environment, thereby enabling different categories of user to select a preferred interface paradigm from a list of options. Furthermore, the interface enables users to examine queries written in one query interface using any of the other interface paradigms, which is useful for sharing queries in the multi-paradigm context, and for helping users familiar with one approach to learn another. The system has been prototyped using the ADAM object-oriented database system, and an experimental comparison of different interaction modes has been conducted.

Abstract This paper describes the design, implementation and initial evaluation of a graphical dialogue specification language and its interpreter. Features of the system include a hierarchical dialogue structure with the capability to export options to lower levels of the hierarchy, the use of a restricted form of production rule approach to option selection in each unit of the dialogue, and suspended time editing (allowing modification of the dialogue specification during execution without loss of context).

A method is described of generating polygonal line approximations to curves defined as conic sections, using only 16-bit integer arithmetic.Integer analogs of the parametric forms of conic section definitions are employed, with table look-up for the trigonometric functions and a fixed-point square root algorithm derived from the subtraction method commonly used with mechanical calculators.For computers without floating-point hardware the method offers significant advantages over direct software simulation of floating-point hardware instructions.

Abstract A non‐recursive algorithm for the traversal of a binary tree is presented in which the order of traversal is defined by an external data array, allowing any of the six possible orders to be selected without modification to the algorithm itself. The extra storage requirements are three pointer variables and two bits per node (or two bits per level if an auxiliary stack is used.) The algorithm is a generalization of the pointer reversal method of Schorr and Waite and is derived by transformation of a generalized recursive version. The algorithm is described using the notation and conventions of Pascal.

Abstract The development of a comprehensive two‐dimensional graphics package for an ICL 4130 with a high‐speed data link to a DEC PDP‐7 with Type 340 refreshed C.R.T. display and light pen is traced from its origin as a package of ALGOL procedures for graphical output. The design criteria imposed by the requirements for light‐pen tracking and identification of picture parts are described, and decisions which affected the subsequent development of the sysetm are identified and commented upon. The various types of display file editing which may be performed are described, and a facility mentioned for saving display files on the backing store of the PDP‐7. The idea of a ‘fixed‐function satellite’ is introduced and its potential usefulness in other operating environments discussed.