Heading:qjk40(635)
IDL DESIGN:  Design Documentationy756qjk40
Page Numbers: Yes  X: 527  Y: 10.5" qjk40
XEROX Palo Alto Research Center						9 February 1977
Inter-Office Memorandumz18592y762\f2 5f5 1b25f0B6f5 15f0 1f5b
To	IDL Group	From	Beau Sheilz18592l4445d2998e18(0,65535)(1,4445)(2,14371)(3,13411)(4,15796)(5,11684)(6,14146)\2t2 1t0 9t4 1t0 4t5 1t0
File	<IDL>Design.Documentation	IDL Design Note Number:  1e12qjk40(2,11695)(4,65535)(5,65535)(6,65535)\30t4 1t0
Subject	 Design Documentation Systeme12qjk40(635)\7t2 1t0
This document describes the initial set of design memos for the IDL project and the method by which that set is to be extended to comprise the specifications for the INTERLISP version of IDL.e18j
At this time there are three design memos:l7447d2999e18j
1.  Design.Documentation	which deals with the design documentation system (This Memo).l7447d2999j
2.  Design.PPLFlaws	which catalogues the known flaws in the PPL versionl7447d2999j(0,65535)(1,7447)(2,65535)(3,65535)
3.  Design.Extensions	which catalogues known and straightforward extensions and revisions to the PPL design which have accumulated from its users' experience.l7447d2999j
Two other design memos are under development:l7447d2999e18j
4.  Design.DeepIssues	which catalogues a set of known problem areas in the PPL design which require substantial thought to resolve and/or which would have a major impact on the basic structures of the system.l7447d2999j\21t2 1t0
5.  Design.DeclExamples	which gives some example programs from the PPL code and suggests a set of declarations that might be useful for these programs.l7447d2999j
The mechanics of maintaining the specification as it develops out of discussions over the next few months is important.  I propose that the design cycle be recorded in a series of memos (of which these five will be the first) which are sequentially numbered, and reside in the IDL directory (or the IDL documentation directory, if we create one) as Bravo format files under names of the form Design.x for a memo on topic x.  The complete series of such memos will constitute the design specifications of the project at any given point.  This seems to be the least painful way of getting all the decisions down, but it involves a commitment on all our parts to write decisions down as they are made, rather than holding them up to the end.e18j(635)\399i1I21i1I
The development of the design notes in the immediate future is expected to proceed as follows.  On the basis of discussions during the next week, a subset of the issues raised in memo 4 will be selected for further discussion, on the basis of perceived importance and tractability, and more detailed design proposals will be drawn up.  Each of these should be the subject of at least one design note.  Although some problems raised in that memo will not be treated during the first implementation, their discussion should encourage awareness of directions in which the system should be made flexible.e18j
Likewise, as a result of discussions on memo 5, specifications for the declarative facilities to be used in the LISP code will also be drawn up as a design memo.  The series will proceed from there in an interrupt driven fashion.e18j
 e18j