The Sequence Abstraction in the Implementation of Emily

Abstract

Emily is a general purpose computer aided lllstruction language with a novel nnplementatlon At the user s level, Emily consists of two languages an mstruction language, wlu.ch 1s used by authors to prepare lessons and a command language for controlling access to lessons, registenng users and other system functions In nnplementation, such a system poses the problem of stonng and controllmg a wide vanety of data types under program control and on backmg store Both storage and control are handled by a data base manager whose basic urut 1s a sequence Tlu.s paper gives a bnef descnption of the Emily languages and then concentrates on the sequence abstraction It 1s shown how tlu.s provides an effective mterface between concepts m the lu.gh level implementation language (Pascal) and the details of the realization of many different data types m a smgle system Fmally, the mtemal representation of sequences 1s discussed