This sub-clause describes the key SGML constructs on which HyTime relies. In typical documents, examples of elements would be paragraphs, chapters, headings, figures, and tables. In hypermedia documents, some examples are hyperlinks of various types, event schedules, events, and objects encoded in a variety of data notations. For example, the owner of a chapter or revision date of a table. Many element types have an ID attribute, which provides a label for each element of that type so that it can be referenced explicitly from any place in the document.
Entities are independent of elements.
For example, an entity could contain part of a picture element or one and one-half paragraph elements. This technique provides the flexibility necessary to accommodate a wide variety of applications. Processors that act on the semantic objects and their data content do not operate directly on the source representation. In the case of SGML, an SGML parser processes the source document to recognize markup and data and provides information about what it found to a processing application. The processing application then operates on its particular abstraction derived from the result of parsing the document.