Since a DTD represents a grammar, it can be visualized graphically as a tree. The visualization in this document uses the notation given in Graphical notation of DTDs.
Figure 1: Graphical notation of DTDs
The meaning of the symbols is:

PCDATA
The element content is Processable Character Data (PCDATA). This is data that consists of zero or more characters of both text and markup. PCDATA is used to indicate that all markup delimiters defined in the SGML declaration will be recognized by the parser as markup in the given element rather than data characters.
RCDATA
The element content is Replaceable Character Data (RCDATA) . this is data that consists of zero or more characters, in which references to substitutions are not recognized (i.e. RCDATA may contain text and entity references (starting with "&") , but no sub-elements).
CDATA
Character Data (CDATA) consists of zero or more text characters, where no markup of any kind is recognized.
ANY
a terminal type indicating that the object may contain text or any element defined in the model.
EMPTY
a terminal type keyword used to indicate that there is no data (i.e. no content, sub-elements or end-tags) for the object allowed in the document instance. This keyword is often used to describe elements that are placeholders or are pointers to external or system-generated data.
One
indicates that the element or the model group occurs exactly once.
ZERO-OR-ONE
indicates that the element or the model group is optional.
ONE-OR-MORE
indicates that the element or the model group occurs multiple times but at least once.
ZERO-OR-MORE
indicates that the element or the model group occurs multiple times but also can be missed (optional).
ORDERED
a connector used to specify that the sibling objects must appear in the document in the order shown in the model.
UNORDERED
a connector used to specify that the sibling objects can appear in any order in the document.
SELECTION
a connector used to specify that only one of the sibling objects can appear in the document.
ELEMENT
indicates a single SGML structure element.
COLLAPSED
indicates, that the content of the element is not displayed here.

 Hint
With respect to XML compliance, the following features are not used:
RCDATA, CDATA, ANY, EMPTY, UNORDERED connection,