(a2ps.info)Glossary
Appendix A Glossary
*******************
This section settles some terms used through out this document, and
provides the definitions of some terms you probably want to know about.
"Adobe"
Adobe is the firm who designed and owns the PostScript language.
The patent that printer manufacturers must pay to Adobe is the
main reason why PostScript printers are so expansive.
"AFM file"
AFM stands for Adobe Font Metrics. These files contain everything
one needs to know about a font: the width of the characters, the
available characters etc.
"Charset"
"Code Set"
Cf. Encoding.
"Delegate"
Another filter (application) which a2ps may call to process some
files. This feature is especially meant for page description
files (Note: Your Delegations).
"DSC"
"Document Structuring Conventions"
Because PostScript is a language, any file describing a document
can have an arbitrary complexity. To ease the post-processing of
PostScript files, the document should follow some conventions.
Basically there are two kinds of conventions to follow:
Page Independence
Special comments state where the pages begin and end. With
these comments (and the fact that the code describing a page
starts and ends somewhere, which is absolutely not necessary
in PostScript), very simple programs (such as `psnup',
`psselect' etc.) can post process PostScript files.
Requirements
Special features may be needed to run correctly the file.
Some comments specify what services are expected from the
printer (e.g., fonts, duplex printing, color etc.), and other
what features are provided by the file itself (e.g., fonts,
procsets etc.), so that a print manager can decide that a
file cannot be printed on that printer, or that it is
possible if the file is slightly modified (e.g., adding a
required font not known by the printer) etc.
The DSC are edited by Adobe. A document which respects them is
said to be "DSC conformant".
a2ps follows all the DSC.
"Duplex"
"DuplexTumble"
"DuplexNoTumble"
To print "Duplex" is to print double-sided. There are two ways to
print Duplex depending whether the second face is printed
upside-down or not:
"DuplexTumble"
DuplexTumble is suitable when (if it were to be bound) the
document would be bound along the short edge (for instance
when you are printing booklets).
"DuplexNoTumble"
DuplexNoTumble corresponds to binding along the long edge of
the medium. A typical case is when printing one-up.
"Encoding"
Association of human readable characters, and computers' internal
numbered representation. In other words, they are the alphabets,
which are different according to your country/mother tongue.
E.g.: ASCII, Latin 1, corresponding to Western Europe etc.
To know more about encodings, see Note: What is an Encoding.
"`Ghostscript'"
"`gs'"
`Ghostscript' (http://www.cs.wisc.edu/~ghost/index.html), `gs' for
short, is a full PostScript interpreter running under many various
systems (Unices, MS-DOS, Mac etc.). It comes with a large set of
output formats allowing many different applications:
_Displaying_
It can be used either to view PostScript files (in general
thanks to a graphic interface such as `Ghostview' or `gv'
...).
_Converting_
To may useful languages/formats: PDF, rewriting in portable
PostScript or Encapsulated PS etc.
_Translating_
to a printer dedicated language, e.g., PCL. In particular,
thanks to `ghostscript', you may print PostScript files on
non PostScript printers.
"Face"
A virtual style given to some text. For instance, _Keyword_,
_Comment_ are faces.
"Headings"
Everything that goes around the page and is not part of the text
body. Typically the title, footer etc.
"Key"
Many objects used in a2ps, such as encodings, have both a key and
a name. The word "name" is used for a symbol, a label, which is
only meant to be nice to read by a human. For instance `ISO Latin
1' is a name. a2ps never uses a name, but the key.
A "key" is the identifier of a unique object. This is information
that a2ps processes, hence, whenever you need to specify an object
to a2ps, use the key, not its name. For instance `latin1' is the
unique identifier of the `ISO Latin 1' encoding.
"Logical page"
Cf. Virtual page.
"lhs"
"left hand side"
See "P-rule".
"Medium"
Official name (by Adobe) given to the output physical support. In
other words, it means the description of a sheet, e.g., A4, Letter
etc.
"Name"
See "Key".
"Page"
A single side of a sheet.
"Page Description Language"
A language that describes some text (which may be enriched with
pointers, pictures etc.) and its layout. `HTML', PostScript,
LaTeX, `roff' and others are such languages. A file written in
those languages is not made to be read as is by a human, but to be
transformed (or compiled) into a readable form.
"PCL"
FIXME:
"PFA file"
PostScript Font in ASCII format. This file can be directly down
loaded to provide support for another font.
"PFB file"
PostScript Font in Binary format. In PFA files there are long
sequences of hexadecimal digits. Here these digits are
represented by their value, hence compressing 2 characters in a
PFA into 1 in the PFB. This is the only advantage since a PFB
file cannot be directly sent to printer: it must first be
decompressed (hence turned into a PFA file) before being used.
"PostScript"
"PostScript" is a page description language designed for _Raster
output devices_. It is even more powerful than that: unlike to
`HTML', or `roff', but as TeX and LaTeX, it is truly a programming
language which main purpose is to draw (on sheets). Most programs
are a list of instructions that describes lines, shades of gray,
or text to draw on a page. This is the language that most
printers understand.
Note that the fact that PostScript is a programming language is
responsible of both its success and its failure. It is a big win
for the PostScript programmer who can easily implement a lot of
nice visual effects. It is a big loss because the page
descriptions can have an arbitrary complexity, hence rendering can
be really slow (remember the first Laser you had, or even
`Ghostscript'. `PDF' has been invented by Adobe to remedy these
problems).
PostScript is a trademark of Adobe Systems Incorporated.
"PPD file"
"PostScript Printer Description file"
These files report everything one needs to know about a printer:
the known fonts, the patches that should be down loaded, the
available memory, the trays, the way to ask it duplex printing,
the supported media, etc.
PostScript has pretended to be a device independent page
description language, and the PPD files are here to prove that
device independence was a failure.
"ProcSet"
Set of (PostScript) procedures.
"Prologue"
PostScript being a language, a typical PostScript program (i.e. a
typical PostScript file) consists of two parts. The first part is
composed of resources, such as fonts, procsets, etc. and the
second part of calls to these procedures. The first part is
called the "prologue", and the second, the "script".
"P-rule"
Pretty printing rule. It is composed of a "left-hand side",
("lhs" for short), and a "right-hand side", ("rhs"). The lhs
describes when the rule is triggered (i.e., the pattern of text to
match), and the rhs specifies the pretty printed output. Note:
P-Rules, for more semantical details, and see Note: Syntax for
the P-Rules, for implementation.
"`psutils'"
The "psutils"
(http://www.dcs.ed.ac.uk/home/ajcd/psutils/index.html) is a set of
tools for PostScript post processing written by Angus Duggan
(http://www.dcs.ed.ac.uk/home/ajcd/). They let you resize the
frame into which the page is drawn, reorder or select pages, put
several pages onto a single sheet, etc. To allow the `psutils' to
run correctly, the PostScript files must be DSC conformant, and
the bad news is that many PostScript drivers produce files which
are not. For some common cases (e.g., Micro$oft tools), Angus
Duggan included in the package some tools (named `fix...ps') to
fix typical problems. `fixps' is a collection of recipes on when
to run what `fix' tool.
"Raster Image Processor"
"RIP"
The hardware and/or software that translates data from a high-level
language (e.g., PostScript) into dots or pixels in a printer or
image setter.
"Raster Output Device"
Behind these words is hidden the general class of devices which
have Pixels that can be addressed individually: Laser, Ink or Dot
printers, but also regular screens etc. It is typically opposed
to the class of devices which _plot_, i.e., have a pen that they
move on the paper.
"rhs"
"right hand side"
See "P-rule".
"RIP"
See "Raster Image Processor".
"Script"
See "Prologue".
"Sheet"
The physical support of the printing: it may support one or two
pages, depending on your printing options.
"Style sheet"
Set of rules used by a2ps to give a face to the strings of a file.
In a2ps, each programming language which is supported is defined
via one style-sheet.
"Tumble"
See "Duplex".
"Virtual page"
Area on a physical page in which a2ps draws the content of a file.
There may be several virtual pages on a physical page. ("virtual
page" is the name recommended by Adobe).
automatically generated by info2www version 1.2.2.9