The constituent components of XML DTD Documents.
DTDs are made up by the following integrants:
- Elements
- Attributes
- Entities
- PCDATA
- CDATA
Brief explanation of each of the integrants :
Elements
Elements are the main constituent components of both
XML documents.
Elements can contain text, other elements, or be empty
eg..
<To>Rohan</To> <From>Amit</From> |
Attributes
Attributes provide extra information about elements.
Attributes are always placed inside the opening tag of
an element. Attributes always come in name/value pairs. The following "img"
element has additional information about a source file:
<img src="computer.gif" /> |
The name of the element is "img". The name of
the attribute is "src". The value of the attribute is "computer.gif".
Since the element itself is empty it is closed by a " /".
Entities:
Entities are expanded when a document is parsed by a
XML parser. Some characters have a special meaning in XML, like the less than
sign (<) that defines the start of an XML tag , the greater than sign (>)
that defines the end of a XML tag.
The following entities are predefined in XML:
| Entity References | Character |
|---|---|
| < | < |
| > | > |
| & | & |
| " | " |
| ' | ' |
PCDATA:
PCDATA means parsed character data. It can be
thought as the character data ( text ) found between the start tag and the end
tag of a XML element.
PCDATA is a text to be parsed by a parser. The
text is checked by the parser for entities and markup.
Tags inside the text will be treated as markup and
entities will be expanded. However, parsed character data should not contain any
&, <, or > characters. These should be represented
by the & , <, and > entities,
respectively.
CDATA:
CDATA is character data that will NOT be parsed by a
parser. Tags inside the text will NOT be treated as markup and entities will
not be expanded.