A system identifier is a document processing construct introduced in the HyTime markup language as a supplement to SGML. It was subsequently incorporated into the HTML and XML markup languages.
In HyTime, there are two kinds of system identifier: formal system identifier (FSI) and simple system identifier.
In HTML and XML, a system identifier is a fragmentless URI reference. It typically occurs in a Document Type Declaration. In this context, it is intended to identify a document type which is used exclusively in one application, whereas a public identifier is meant to identify a document type that may span more than one application.
In the following example, the system identifier is the text contained within quotes:
Famous quotes containing the word system:
“Nobody is glad in the gladness of another, and our system is one of war, of an injurious superiority. Every child of the Saxon race is educated to wish to be first. It is our system; and a man comes to measure his greatness by the regrets, envies, and hatreds of his competitors.”
—Ralph Waldo Emerson (1803–1882)