.TL
Standard Nomenclature

.SH
AAS
.IP
The American Astronomical Society.
.SH
C
.IP
C is a powerful modern language for both systems and general programming.
C provides data structuring, recursion, automatic storage, a fairly
standard set of control constructs, a rich set of operators,
and considerable conciseness of expression.  Developed by Ken Thompson
and Dennis Ritchie at Bell Labs in the early 1970's, C is the language
used to implement the kernel of the UNIX operating system, as well as
the standard UNIX utilities.
.SH
CL
.IP
The IRAF Command Language.  The CL is an interpreted language designed
to execute external \fBtasks\fR, and to manage their \fBparameters\fR.
The CL organizes tasks into a hierarchical structure of independent
\fBpackages\fR.  Tasks may be either \fBscript tasks\fR, written in
the CL, or compiled \fBprograms\fR, written in the SPP language, and
linked together to form \fBprocesses\fR.  A single process may contain
an arbitrary number of tasks.
.IP
The CL is itself both a task and a process.  The CL process runs
concurrently with the subtasks which it executes.  The CL process and
the process containing the subtask being executed communicate dynamically
via interprocess communication, providing both a highly interactive mode
of execution, as well as a batch mode.
.IP
The CL provides \fBredirection\fR of all i/o streams, including graphics output
and cursor readback.
Other facilities include \fBmenus\fR, \fBcommand logging\fR,
parameter \fBprompting\fR, an online \fBhelp facility\fR, a "programmable desk
calculator" capability, and a \fBlearn mode\fR.
New packages and tasks are easily added by the user,
and the CL environment is maintained in the user's own directories,
providing continuity from session to session.
.SH
CLIO
.IP
CL I/O.
A package of SPP callable library routines, used to communicate with the CL.
.SH
FIO
.IP
File I/O.
A package of SPP callable library routines, used to access files.
.SH
FITS
.IP
A "Flexible Image Transport System".  FITS is
a standard data format used to transport images (pictures) between computers
and institutions.  Developed in the late 1970s by Donald Wells (KPNO) and
Eric Greisen (NRAO), the FITS standard is now widely used for the
interchange of image data between astronomical centers, and is officially
sanctioned by both the AAS and the IAU.
.SH
FMTIO
.IP
Formatted I/O.
A package of SPP callable library routines, used to perform formatted
i/o (decoding and encoding of character strings).
.SH
Fortran
.IP
As the most widely used language for scientific computing for the past
twenty years, Fortran needs no introduction.  Fortran is used in the 
IRAF system as a sort of "super assembler" language.  Programs and procedures
written in the IRAF SPP language are mechanically translated into a highly
portable subset of Fortran, and the Fortran modules are in turn translated
into object modules by the host resident Fortran compiler.  Existing numerical
and other modules, already coded in the Fortran language, are easily linked
with modules written in the SPP language to produce executable programs.
The IRAF system and applications software does not use any Fortran i/o;
all i/o facilities are provided by the IRAF \fBprogram interface\fR and
\fBvirtual operating system\fR.
.SH
GIO
.IP
Graphics I/O.
A package of SPP callable library routines, used to interface to
graphics and grayscale devices.
.SH
IAU
.IP
The International Astronomical Union.
.SH
IMIO
.IP
Image I/O.
A package of SPP callable library routines, used to access imagefiles
(bulk data arrays).
.SH
IRAF
.IP
The IRAF or "Image Reduction and Analysis Facility", consists of a
virtual operating system, a command language, a general purpose
programming language (which was developed especially for IRAF),
a large i/o library, a numerical library, and numerous support utilities
and scientific applications programs.  The system is designed to be
transportable to any modern superminicomputer.  When completed, the
system will provide extensive facilities for general image processing,
astronomical data reduction and analysis, scientific programming,
and general software development.
.SH
Lroff
.IP
The Lroff text formatter is part of the portable IRAF system.
The online \fBhelp\fR facilities use Lroff, and hence manual pages
and other online documentation must be maintained in Lroff form.
The Lroff text formatter is patterned after the UNIX \fITroff\fR
text formatter.
.SH
MTIO
.IP
Magnetic Tape I/O.
A package of SPP callable library routines, used to read and write
magnetic tapes.
.SH
Make
.IP
Make is a UNIX utility program, used to compile and link
(make) programs.
Make takes as input a human readable \fIMakefile\fR which
describes the interdependencies of the modules in the package,
as well as giving exact instructions for making each module.
When making a target module, Make recompiles only those
modules which have been changed since the target was last made.
A simple command like "make all" usually suffices to make all of
the modules in a package.
.IP
Make is most useful on UNIX systems.  Even on non-UNIX
systems, however, the makefile for the package is useful documentation,
for it describes precisely how to make each module in the package.
.SH
Mklib
.IP
Mklib is a UNIX dependent utility developed for IRAF.
Mklib is analogous to Make, except that Mklib is used to maintain libraries.
Mklib checks each module in a library to see if it is up to date,
and if not, recompiles the module and installs the new object module
in the library.
Mklib is used by the IRAF Sysgen utility to automatically update
the IRAF system (consisting of four libraries containing several
hundred modules).
.SH
OS
.IP
(1) An acronym for the term "operating system".
(2) The OS interface package, which contains the machine dependent
routines required to interface the portable IRAF i/o packages to the
local operating system.
.SH
OSFN
.IP
An acronym for the term "OS dependent file name".
.SH
SPP
.IP
The IRAF Subset Preprocessor Language (SPP), implements a subset of the
full language scheduled for development in 1984.  The SPP language is
a general purpose language, patterned after Ratfor and C.
The language provides advanced capabilities, modern control constructs,
enhanced portability,
and support for the IRAF runtime library (CL interface, etc.).
.SH
Troff
.IP
Troff is the UNIX text formatter.  In IRAF documentation,
\fITroff\fR is always used in conjunction with the "ms" macro package.
.SH
UNIX
.IP
An operating system developed at Bell Labs in the early 1970s by
Ken Thompson and Dennis ritchie.  Though originally developed for
the PDP11, UNIX is now available on a wide range of machines,
ranging from micros to superminis and mainframes.  UNIX is the
software development system for the IRAF project.
.SH
VFN
.IP
An acronym for the term "virtual file name".  A virtual file name is
a machine independent filename of the form "ldir$root.extn".
.SH
VMS
.IP
The native operating system for Digital Equipment Corporation's VAX
series of supermini computers.
.SH
VOPS
.IP
The "vector operators" package, a package of SPP callable library
routines providing a wide class of vector pseudo-instructions.
The VOPS routines are written in the SPP language, but may be
optimized in assembler or interfaced directly to an array processor,
depending upon the implementation.
.SH
band
.IP
The Nth band of a three dimensional array or image is denoted
by the subscript [\(**,\(**,N],
where \(** refers to all the pixels in that dimension.
A band is a two dimensional array.
.SH
binary file
.IP
A binary file is an array or sequence of \fBchars\fR, where
the term char defines a unit of storage, and implies nothing
about the contents of the file.
Data is transferred between a binary file and a buffer in the
calling program by a simple copy operation, without any form of conversion.
Binary files are created, deleted, and accessed via the
routines in the FIO interface.  Barring device restrictions,
binary files may be accessed at random, and extended indefinitely.
Almost any device may be accessed as a binary file via FIO.
.SH
binary operator
.IP
An operator which combines two operands to produce a single result
(i.e., the addition operator in "x + y").
.SH
brace
.IP
The left and right braces are the characters "{" and "}".  Braces
are used in the CL and in the SPP language to group statements to form
a compound statement.
.SH
bracket
.IP
The left and right square brackets are the characters "[" and "]".
Brackets are used in the SPP language to form array subscripts.
.SH
byte
.IP
The \fBbyte\fR is the smallest unit of storage on the host machine.
The IRAF system assumes that there are an integral number of bytes
in a \fBchar\fR and in an address increment (and therefore that the
byte is not larger than either).
On most modern computers, a byte is 8 bits, and a char is 16 bits
(INTEGER\(**2).  If the address increment is one byte, the machine
is said to be \fBbyte addressable\fR.  Other machines are \fBword
addressable\fR, where one word of memory contains two or more bytes.
In the SPP language, SZB\(ulCHAR gives the number of bytes per char,
and SZB\(ulADDR gives the number of bytes per address increment.
.SH
char
.IP
The \fBchar\fR is the smallest signed integer which can be
directly addressed by programs written in the SPP language.  The char
is also the unit of storage in IRAF programs: the sizes of objects are
given in units of chars, and binary files and memory are addressed in
units of chars.  Since the SPP language interfaces to the machine via the
local Fortran compiler, the Fortran compiler determines the size of a char.
On most systems, the datatype \fBchar\fR is equivalent to the (nonstandard)
Fortran datatype INTEGER\(**2.
.SH
column
.IP
The Nth column vector of a two dimensional array or image is denoted
by the subscript [N,\(**],
where \(** refers to all the pixels in that dimension.
The Nth column of the Mth band of a three dimensional array or image
is denoted by [N,\(**,M].
.SH
compiler
.IP
A compiler for a language X is a program which translates a \fBsource
module\fR written in the language X into an \fBobject module\fR.
A \fBlinker\fR subsequently combines a number of object modules to
produce an executable \fBprocess\fR.
.SH
coupling
.IP
Coupling measures the strength of relationships between modules.
The independence of modules is maximized when coupling in minimized.  
A change in one module is least likely to require a change in another
module when the two modules are minimally coupled.
.SH
data structure
.IP
A data structure is an aggregate of two or more data elements.
Examples include arrays, descriptors, files, records, linked lists, 
trees, graphs, and so on.
.SH
database management
.IP
Database management is a branch of computing science concerned with
techniques for implementing, maintaining, and accessing databases.
Databases may be used to store arbitrarily complex data objects.
A database is self describing and self contained.  Access to a database
typically occurs only through well defined interfaces, which ideally
provide a high degree of \fBdata independence\fR (the external world
knows no more than needed about the contents of the database, or how
data is stored in the database).
.IP
Applications programs communicate with one another via records passed
through the database, as well as save final results in the database.
A general purpose query language can be used to inspect and manipulate
the contents of a database.
.SH
datafile
.IP
A datafile is a database storage file.  Datafiles are used to store
program generated \fBrecords\fR or descriptors, containing the results
of the analysis performed by a program.  Datafile records may be the
final output of a program, or may be used as input to a program.
.SH
field
.IP
A field is an element of a structure or record.  Each field has
a name, a datatype, and a value.
.SH
function
.IP
A function is a procedure which returns a value.  Functions must be
declared before they can be used, and functions must only be used in
expressions.  It is illegal to \fBcall\fR a function.
.SH
header file
.IP
A header file is a file (extension ".h") containing only defined
constants, structure definitions, macro definitions, or comments.
Header files are included in other files by referencing them in
\fBinclude\fR statements, and are not directly compiled.
.SH
identifier
.IP
An identifier is a sequence of characters used to name a procedure,
variable, etc. in a compiled language.  In the SPP language, an identifier
is an upper or lower case letter, followed by any number (including zero)
of upper or lower case letters, digits, or instances of the underscore
character.
.SH
image
.IP
An array of arbitrary dimension and datatype, used for bulk data storage.
An image is an array of \fBpixels\fR.
.SH
imagefile
.IP
The form in which images are implemented in the IRAF system.  The IRAF
currently supports images of up to seven dimensions, in any of eight
different datatypes.  Only \fBline storage mode\fR is currently available.
The "imagefile" structure is actually implemented as two separate files,
the \fBimage header file\fR and the \fBpixel storage file\fR.
.SH
include file
.IP
An "\fBinclude\fR \fI<include\(ulfile\(ulname>\fR"
statement in the SPP language is replaced during compilation by the
contents of the named include file (the contents of the include
file are inserted into the input stream).
.SH
interface
.IP
The interface to a module is \fIdefined\fR by the \fBexternal specifications\fR
of the module.  The \fIactual\fR interface to a module is everything that
is known about the module by other modules in the system.  The interface to
a subroutine library, for example, is defined by the manual pages, reference
manuals, and other formal documentation for the library.
.SH
line
.IP
The Nth line of a two dimensional array or image is denoted
by the subscript [\(**,N],
where \(** refers to all the pixels in that dimension.
The Nth line of the Mth band of a three dimensional array or image
is denoted by [\(**,N,M].
.SH
list file
.IP
A list file is a text file, each line of which is a record containing
one or more fields.  Each record in the list has the same format,
though not all fields need be present (fields can only be omitted
from right to left).
.SH
macro
.IP
A macro, or \fBinline function\fR, is a function with zero or more arguments,
which is expanded by text substitution during the preprocessing phase
of compilation.
.SH
newline
.IP
The newline character ('\\n') delimits each line of text
read by the FIO input procedures.  If a text file is read character
by character, a single newline character marks the end of each line,
and the special character EOF marks the end of the file.  Newline is
logically equivalent to a carriage return followed by a line feed.
.SH
operand
.IP
An operand is a data object which is operated upon by an operator, 
procedure, or task.  Operands may be either input or output, or both.
.SH
package
.IP
A package is a set of modules which operate on a specific \fBabstract
datatype\fR.  The modules in a package may be either procedures or
tasks.  Examples of abstract datatypes include the CL, the file,
the imagefile, and so on.
Some packages are merely collections of modules which
are logically related (i.e., the class of system utilities).
.SH
parameter
.IP
An externaly supplied argument to a module which directly controls
the functioning of the module.
.SH
pathname
.IP
An absolute OS dependent filename specification, i.e, a filename which
is not an offset from the current directory.
.SH
pixel
.IP
The fundamental unit of storage in an image; a picture element.  An image
is an array of pixels.
.SH
pointer
.IP
A pointer is a datum which defines the coordinates of an object in
some logical coordinate system.  To use a pointer, one must know what
type of object the pointer points to, and what coordinate system the
pointer references.
.SH
portable
.IP
A program is said to be \fBportable\fR from computer A to computer B
if it can be moved from A to B without change.  A program is said
to be \fBtransportable\fR from computer A to computer B if the effort
required to move the program from A to B is much less than the effort
required to write an equivalent program on machine B from scratch.
.SH
preprocessor
.IP
A preprocessor is a program which transforms the text of a source file
prior to compilation.  A preprocessor, unlike a compiler, does not fully
define a language.  A preprocessor transforms only those constructs which
it understands; all other text is passed on to the compiler without change.
.SH
procedure
.IP
A separately compiled program unit.  The procedure is the main construct
provided by languages for the \fIabstraction of function\fR.
The external characteristics of a procedure are its name, argument list,
and optional return value.
.SH
process
.IP
An executable partition of memory in the host computer.
The host OS initiates a process by copying or mapping an executable file
into main memory.
In a multitasking, multiuser system, a number of processes
will in general be simultaneously resident in main memory,
and the processor will execute each in turn,
performing many \fBcontext switches\fR each second with the result that
all processes appear to be executing simultaneously.
.SH
program
.IP
A program is a compiled procedure which is called by the CL,
via the CL interface.
The procedure must be referenced in a \fBtask\fR statement before it
can be accessed by the CL, and must not have any formal arguments.
A program communicates with the CL via CLIO.
An arbitrary number of programs may be linked to form a single \fBprocess\fR.
.SH
program interface
.IP
The interface between an applications program and the outside world.
The program interface is subdivided into a number of \fBpackages\fR,
each of which has a well defined interface of its own.
The specifications of the program interface are summarized in the
program interface \fBcrib sheet\fR.
.SH
record
.IP
A record is data structure consisting of an arbitrary set of fields,
used to pass information between program modules,
or to permanently record the results of an analysis program
in a \fBdatabase\fR.
Often, records are organized into arrays, where each record
contains the results of the analysis of a particular object.
.SH
script task
.IP
An interpreted program written in the command language.  A script task,
like a compiled program, may have formal parameters and local variables.
A script task may call another task, including another script task,
but may not call itself.
To the caller, script tasks and compiled programs are equivalent.
.SH
specifications
.IP
A detailed description of a software system or subsystem,
concentrating on the external attributes of the software rather than
the on the implementation.  \fBRequirements\fR are similar to specifications,
but are usually more formal and less detailed.  The specifications for
a subsystem define the interface to the subsystem,
and when written in an informal style may resemble a reference manual.
.SH
system interface
.IP
The interface between the portable IRAF software and the host operating
system.  The system interface is a \fBvirtual operating system\fR.
The system interface routines, maintained in the "OS" package,
are in principle the only part of a system that needs to be changed
when porting the system to a new computer.
.SH
task
.IP
A CL callable program unit.  CL tasks may be script tasks, external programs,
or compiled procedures which are built in to the CL.
.SH
task statement
.IP
(1) The \fBtask\fR statement in the SPP language defines a list of programs
to be linked together to form a single process.
(2) The CL \fBtask\fR statement enters the name of a task in the dictionary,
defines the type of task, and in the case of a compiled task, the name of
the process in which it resides.
.SH
text file
.IP
A file which contains only text (character data), and which is maintained
in the form expected by the text processing tools of the host OS.
.SH
unary operator
.IP
An operator which operates on a single operand, i.e., the minus sign in
the expression "\(mix", or the boolean complement operator in the
expression "!x".
.SH
virtual memory
.IP
If the address space of a process exceeds the amount of physical memory
which the process can directly address, the process is using virtual memory.
The virtual address space is organized into a series of fixed size \fBpages\fR.
The amount of physical memory available to a process is known as the
\fBworking set\fR of a process.  Pages which are not \fBmemory resident\fR,
i.e., not in the working set, reside on some form of backing store, usually
a disk file.  When a page is referenced which is not in the working set,
a \fBpage fault\fR occurs, causing the page to be read into the working set.
If the pattern of memory accesses is such that a page fault occurs on nearly
every access, the process is said to be \fBthrashing\fR, and will run
exceedingly slowly.
.SH
virtual operating system
.IP
A package of system calls, providing a set of primitive functions comparable
to those provided by an actual operating system, which can be interfaced
to a number of actual operating systems.
The IRAF virtual operating system provides routines (the so-called
\fBz-routines\fR) for file access, process initiation and control,
interprocess communication, memory management,
magtape i/o, exception handling, logical names, and time and date.
.SH
whitespace
.IP
A sequence of one or more occurrences of the characters blank or tab.
.SH
z-routines
.IP
Machine dependent routines, used to interface to the host operating
system.  The IRAF z-routines are maintained in the package "OS".