Page Description Languages
A page description language (PDL) is a language that describes the appearance of a printed page in a higher level than an actual output bitmap. An overlapping term is printer control language, but it should not be confused as referring solely to Hewlett-Packard's PCL. PostScript, one of the most noted page description languages, is a fully fledged programming language, but many PDLs are not complete enough to be considered a programming language. The markup language adaption of the PDL is the page description markup language.
Page description languages are textual or binary data streams. In principle, the same data stream could be rendered multiple times to generate multiple copies of the same image. They are distinct from graphics APIs such as GDI and OpenGL that can be called by software to generate graphical output.
A page description language (PDL) specifies the arrangement of a printed page through commands from a computer that the printer carries out. Hewlett Packard's Printer Control Language ( PCL ) and Adobe's PostScript are the two most commonly used PDLs.
Modern PDLs describe page elements as geometrical objects, such as lines, arcs, and so on. PDLs define page elements independently of printer technology, so that a page's appearance should be consistent regardless of the specific printer used. The printer itself (rather than the user's computer) processes much of the graphical information. For example, the printer carries out a command to draw a square or a character directly rather than downloading the actual bit s that make up the image of the square or the character from the computer.
Page description languages can be contrasted with content description languages, such as the Extensible Markup Language ( XML ), which describe the content rather than the arrangement of information.