A specific approach to constructing a business information model is described. Various ways of representing this kind of model in a storage structure, based on a few simple assumptions, are then given. The performance tuning for data base access which is possible through choice of data structure is briefly discussed. An educational implementation of a data base representing a model is briefly outlined.

Some computer systems, such as operating systems and communications controllers, have to work continuously for long periods. These systems are almost inevitably affected by intermittent errors, and there is a need to develop design methods which minimise the effect of occasional errors. This paper points out that, if some part of a system can be modelled as a finite state machine, then it is sometimes possible to arrange that this part will reset itself to a correct state after an error. The technique has been used in the design of a simple interactive programming system.

Many databases need to have their contents kept at a high level of accuracy. New kinds of auditing procedures must be devised to ensure this. Inaccuracies arise from various causes; in this paper one particular fundamental aspect of accuracy is isolated—that of consistency of the stored data. Inconsistencies occur when the stored data fails to reflect the rule of compatibility of the elements of the applications world. The expression of the rules governing the generation of the data in the application, and the resulting complexity of validation procedures are investigated through mathematical logic.

attended to by SAD practically immediately as they appear.We have already discussed two major subjects of the operator's decisions; below we list several others:

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An algorithm is described that will recognize, and fully analyze, strings of unbounded length, using the rewriting rules of any context-free grammar. It uses a finite random access store, three pushdown tapes, and a counter. It imposes no restrictions on the grammar defined by the rewriting rules, excepting only that it be a context-free phrase structure grammar. The analysis printed out is a linearized form of the structural description tree (or trees, in an ambiguous case) of the input string. A proof that the analyzer will always stop in a finite time is provided. The upper bound on the running time increases exponentially with input string length.