QUESTION: What is a document-composition engine?

ANSWER: A document-composition engine is a set of software modules that interpret formatting instructions for a particular document and generate code that can be rendered on a computer screen or on a printer so the document can be seen and understood by humans.

People in the printing & publishing industry sometimes refer to a document-composition engine simply as a "composition engine."

Many document-composition engines can generate a variety of output formats. An output format is a particular kind of code that is understood by a printer, a RIP, or a software program that displays documents on a computer monitor.

Here are few examples of common output formats that are generated by document-composition engines.

  • PostScript: Many printers and RIPs understand PostScript.

  • PCL: Many printers and RIPs understand PCL.

  • PDF: Some software applications that display documents on a computer monitor understand PDF. For example, the Adobe Acrobat software, the Adobe Reader software, and the Jaws PDF Editor software understand the PDF format.

  • JPEG, TIFF, BMP: Some software applications that display documents on a computer monitor understand these formats. For example, Microsoft Word, Adobe Photoshop, and Adobe Illustrator understand these formats.

Well-designed document-composition engines that are geared specifically for the purpose of producing variable-data documents can generate special optimized output formats that are targeted for particular printers and RIPs. Some of these special optimized output formats are VPS, Fiery FreeForm, and PPML. When you are producing variable-data documents, it is very important to use a document-composition engine that generates an output format that works well with your printer/RIP. Otherwise, your documents might print very slowly — or worse, you might not be able to print the documents at all.

Often but not always, software applications that you use to create documents do not generate the output formats directly. Instead, sometimes these applications generate an intermediate code format, and then another software program called a "driver" converts the intermediate code to the output format that is needed. For example, if you use Microsoft Word on a Windows computer to write a letter, you will probably be printing the letter on a printer that understands the PCL language or the PostScript language. However, Microsoft Word itself doesn't generate PCL code or PostScript code. Instead, Microsoft Word generates an intermediate code format, and then a PCL printer driver or a PostScript printer driver converts the intermediate code format to either PCL or PostScript so your printer can print the letter.