Secure XML: The New Syntax for Signatures and Encryption

3.6. XML Document Physical Structure

An instance of XML is a hierarchical set of entities. Entities constitute the physical structure of an XML document. Figure 3-7 shows the different types of entities other than the special document entity.

Figure 3-7. Entity types

XML uses entities to represent special characters, to represent repetitious text, and to include the content of other files. These storage units of XML documents contain particular parts of the document [Harold]. Namely, an entity contains either text or binary data—but not both. It may be a file, a database record, or a network resource. Entities also contain either parsed or unparsed ...