Re: Usage of "mapping"

Subject: Re: Usage of "mapping"
From: Ben Kovitz <apteryx -at- CHISP -dot- NET>
Date: Mon, 28 Jun 1999 10:23:58 -0600

Nana Kato asked:

> Would someone please let me know in what situation "map" (verb)
> is used?
> The The Adobe PDFMaker's manual states:
> >The Heading-to-Bookmark options group allows you to control how
> >Word heading styles are mapped to PDF bookmarks.
> I often see "map" used in software documentations. I'm not sure
> about this usage but my hunch is that "map" is used to mean
> "apply" or "assign" in a technical context. (An ordinary English
> dictionary defines "map" only to mean 1. make a map, 2. make
> something well-known. From this I thought this usage is rather
> technical-specific.)

A "mapping" in this sense of the word is a concept from
mathematics, used frequently in computers. A mapping a set of
correspondences between two other sets (or more than two). It
can be defined by a rule, like "every dark line on this piece of
paper corresponds to a road", or simply by listing each element
from one set along with its corresponding element(s) in the
other set, like a list of ISBN numbers and corresponding book

In your example above, one of the two "other sets" is Word
heading styles. The other is the corresponding PDF bookmarks. A
mapping between them is a big list, which pairs each Word heading
style with a corresponding PDF bookmark.

This concept is all over the place in the computer field (and
everywhere else). In an accounting system that gives a customer
number to every customer, there is a mapping between customer
numbers and customer names. Every code is a mapping. For
example, ASCII is a mapping between numbers in the range 0..127
to characters.

You can think of every mapping as equivalent to a two-column
table. Each item in the left column "maps" to a corresponding
item in the right column.

As a verb, "map" means to participate in such a relationship, as
in the previous sentence.

In a closely related sense of the word, software that inputs
items from one "column" of the mapping and outputs the
corresponding item from the other "column" is said to "map" the
items or to "perform" a mapping. This sense of "map", no doubt,
is what led to the passive construction in the example: the
writer means that PDFMaker "maps" Word heading styles to PDF
bookmarks; the user defines the mapping in the
Heading-to-Bookmark options group. Or in other words, PDFMaker
outputs PDF bookmarks that correspond to Word heading styles
("maps" them, or "performs" the mapping) according to a table of
correspondences (the "mapping") that the user defines in the
Heading-to-Bookmark options group.

(In the strict mathematical sense, you can't "perform" a mapping,
since a mapping is just an abstract relationship between sets.)

I agree with Tim Altom that this sense of "map" is something
everyone should know. Well, at least everyone who works with
computers. Or anything else.

Ben Kovitz <apteryx -at- chisp -dot- net>
Author, _Practical Software Requirements: A Manual of Content & Style_

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