APPENDIX B: Glossary The following terms and acronyms are used in SPP, additional terms, generic to IRAF and STSDAS, are defined in the glossary in the STSDAS Users Guide. access mode - How to open a file or image, read-only, read-write, for example. argument - A value passed to a procedure. Also in the cl, a value passed to a task. assignment - Replace the value of a variable. asynchronous error - An error that results in control passing to a proce- dure other than the one in which the error occured. boolean - A binary value, yes or no, true or false. cell array - Grey scale image, sometimes also known as a raster or pixmap. clio - Interaction with the cl. The VOS library of procedures for accessing cl parameters. coercion - (As in type coercion.) Conversion of a value from one data type into another. Commonly by simple assignment of variables. comment - Text in a program file that is not executed and is retained for information purposes. In SPP, comments begin with the # character. common blocks - A set of ariables available to more than one procedure through common memory. compile - To process source code into object code, combined with other procedures to make a program (see "link"). constant - An identifier having a fixed value. data structure - The organization of data in a commonly accessible form. Often includes multiple data types and arrays. data type - The basic attribute of a variable, constant or data value such as integer, floating point (real), double precision, boolean or complex. dimensionality - The number and sizes of axes of an array. double precision - A floating point value having more bits for the mantissa. error - An abnormal condition in a program error handler - A procedure called on an error condition to perform some activity such as closing files and cleaning up memory. escape sequence - Characters including metacharacters that change the interpretation of other characters. The backslash ("\") is an escape to permit specifying a character constant in SPP. file descriptor - A pointer to a structure describing a file. file name template - A file name possibly referring to more than one file, including wild-cards or a list of individual file names, or a pointer to a file containing a list of files. filter - A program that transforms a data set in some way without altering the fundamental structure of the data. fio - Basic binary file I/O not limited to images or any particular structure. flag - A variable indicating one of a set of possible conditions. floating point - A value having a decimal and fractional part. fmtio - Formatted I/O. The procedures for standard text and numeric I/O to files and terminals. function - A procedure returning a value assigned to a variable. gcur - Graphics cursor. Treated by the cl as a cl parameter and accessed in SPP via a clio procedure returning the coordinates of the cursor. generic operator - A function or operator that can be used for any of sev- eral data types. generic preprocessor - The program that converts generic source into com- pilable code specific to a given data type. gio - Graphics I/O. The set of VOS procedures for drawing graphs. graphcap - The file that describes attributes of graphics devices. header parameter - A value stored as part of an image file, used to describe the image. heap memory - Dynamically allocated memory accessed with the malloc family of procedures. identifier - A string or sequence of characters having a recognized meaning such as a variable or procedure name. image section - (see "section.") imcur - Image cursor. A cl parameter type returning coordinates from an image display. imio - Image I/O. The library of procedures for accessing IRAF images. include file - Source code that can be inserted as-is into other source by referring to a file name. index - An integer constant or variable indicating a particular element of an array. integer - A constant or variable having no fractional part. intrinsic function - A function built in to the language. In general, the data type of the arguments and returned value may be any valid data type. kernel - The low-level routines implementing the system. The system pro- cedures dealing with a particular image format. The "device driv- ers" for rendering graphics on a class of devices. keyword - An identifier or character string reserved for some purpose such as image header parameters. learning - The capability of the IRAF cl to remember the value of a task parameter from execution to execution. library - A file containing compiled procedures (object code) and linked with an application. link - Combine compiled code to make an executable program. logical task - An IRAF task implemented as part of a package or physical task. longword boundary - Locations in data memory separating the longest addressable units of data. macro - A string identified with a symbol and replaced by string substitu- tion in code. mask - An image whose values indicate particular properties of another image or matching size. A mask might specify bad detector element or relative errors of pixels. matrix - A grouping of values in a rectangular array. memio - The VOS library of procedures for dynamically allocating mem- ory. metacharacters - Literal characters interpreted by a parser. mii - Machine Independent I/O. A method of converting data that is inde- pendent of the host computer architecture. The library of proce- dures to perform these conversions. mixed mode - An expression involving variables or constants of different data types. mkpkg - The program that combines compiling, linking and maintaining source and objects. mode - Manner in which CL handles prompting and learning when dealing with parameters. mtio - Magnetic tape I/O. mwcs - Mini World Coordinate System. NDC - Normalized Device Coordinates. A graphics coordinate system rel- ative to the device. newline - A character interpreted as a delimiter between lines of text. OIF - Old IRAF format. The native IRAF image format consisting of a pair of binary files, a header describing the image and a separate pixel file. operators - Functions combining values in an expression such as +, -, &&. osb - Bit and byte operations. package - A library of procedures grouped by common function or a group of application tasks grouped by common function. parameters - The arguments to a program accessed via clio from the cl. pen - The logical position of drawing graphics. physical task - An executable IRAF program, possibly comprising multiple "logical tasks." plio - Pixel list I/O. pointer - Reference to dynamically allocated memory addresses. predefined constant - A program value defined at compile time, either in a data statement or as a symbolic macro. preprocessor - An operation applied to program source before compilation. The generic preprocessor permits defining common code for multi- ple data types. xc is the preprocessor for converting SPP into For- tran. primitives - Relatively low-level procedures performing well-defined func- tions. procedure - The smallest executable unit of a program, called by another procedure or as a task from the cl. prompt - A request for input from the user via a prompt to the terminal (window). pset - A file containing cl parameters. A pset must be defined as a task in the cl and assigned to another task parameter. The parameter values are then available to an application as any cl parameter. pushback - The opposite of reading from an input stream or file. Data pushed back is then available for reading. QPOE - Quick Position-Oriented Event image; the native image format for the xray analysis package developed by PROS. Ratfor - Rational Fortran. One of the steps in converting SPP into Fortran. scalar - A single-valued variable. section - (As in "image section.") A portion of an IRAF image treated in an application as any image. stack memory - Dynmically allocated memory. STF - STSDAS format images also known as GEIS format. The native image format for HST observations. STF images are largely inter- changeable with OIF images. stream - A source of data logically consisting of a string of characters. The standard input (STDIN), standard output (STDOUT) and standard graphics (STDGRAPH) are the most commonly used streams. string - Sequence of characters enclosed in quotes, for example, "abc". structure - See "data structure." symbolic constant - A numeric value or literal string represented by an identifier. In compiled code, the value replaces the identifier by simple string substitution. task - A program known to IRAF, a command in the cl. templates - See "file name templates." termcap - The IRAF file that describes attributes of text terminals. token - The smallest sequence of characters recognized by a parser, a num- ber or identifier, for example. tty - Terminal I/O. unary operator - An operator requiring only one operand, such as nega- tion. vector - An array, a contiguous group of values accessed through a com- mon variable name. vops - Vector operators. The library of procedures that operate on arrays, potentially optimized for the host architecture. VOS - Virtual operating system. The set of procedures called by an applica- tions tasks for performing IRAF functions. WCS - World Coordinate System. Coordinates associated with data rather than a device or an arbitrary scale. white space - Any number of tabs, spaces or newline characters separating entities in a string. word - The fundamental unit of accessing data in a program, usually sev- eral bytes long. The word size varies between host architectures. xc - The program that compiles and links SPP, Fortran, and C code to pro- duce an executable, or physical task.