🚀 go-pugleaf

In article <BLK.90Oct25142230@vanity.mitre.org>, blk@mitre.org (Brian L. Kahn) writes:
> 
> For some time, I've puzzled over the difference (if any) between a
> specification language and a programming language.  The best I can
> come up with is that a spec has less information about data structures
> and/or algorithms than is usually found in code.  ...

I always used to say "a specification is more abstract than a program"
(there is a continuum here ranging from "low-level" programs to "highly
abstract" specifications - its not an either-or relation). Then I was
challenged to define what I meant by "more abstract". The best definition
I could come up with was SMALLER (and more readable - but the metric
which coresponds most closely to intuitive notions of readablility is size!).
Naturally, for a specification to be smaller it _has_ to contain less
information: the input-output behaviour is arguably the most useful
information to a user of the program, therefore the specification will
have less (or no) information about data structures and algorithms.

A secondary attribute of a good specification is separation of concerns.
For example: one part of the spec will specify "normal" behaviour, another
part will specify the action take under various error conditions. In the
implementation the error handling code will be deeply intertwingled with the
"normal case" code - but they are logically separate and should be separate
in the specification. Another example is a report printing program where
one part specifies the headings and record formats and another part specifies
the pagenation (lines per page, headers and footers on each page, page count
etc.) and perhaps a third part defining the end of report totals as a function
of the whole database. In the implementation these will be deeply mixed, with 
the record formatter incrementing the line count, report totals etc.

	Martin.

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