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:
“The intellect is vagabond, and our system of education fosters restlessness. Our minds travel when our bodies are forced to stay at home. We imitate; and what is imitation but the travelling of the mind?”
—Ralph Waldo Emerson (1803–1882)