The document outlines the structure and components of XML documents, focusing on declaring elements, attributes, and entities. It details the syntax for defining elements and their attributes, including control characters for item occurrences, and distinguishes between internal and external entities. The examples provided illustrate how to implement these concepts in XML DTD (Document Type Definition).

2. 1. Declaring elements
• XML document has number of elements.
• The first node of XML document is called
the root node.
Syntax: <!ELEMENT element-type category>
Ex: <!ELEMENT name(fname, lname)*>

3. Control characters
• Item*
• (item1,item2,item3)
• Item
• (item1,item2)
• (item1/item2)
• Item+
• Item?
• Appears zero or more times.
• Separates items in a sequence.
• Appears exactly once.
• Closes a group of items.
• Only one may appear.
• Appears at least once.
• Appears once or not at all.
Ex: <!ELEMENT recipe(name, ingredients+ ,cooking+ serves?, instruction*)>

4. 2. DTD attributes
• Attributes are additional information
associated with an element type.
• ATTLIST is used to identify attributes for
elements.
• Syntax: <!ATTLIST element-name attribute-
name attribute-type default-value>
<element attribute-name=“attribute-value”>

5. • Ex:
<?xml version=“1.0”>
<!DOCTYPE image[
<!ELEMENT image EMPTY>
<!ATTLIST image height CDATA #REQUIRED>
<!ATTLIST image width CDATA #REQUIRED>
]>
<image height=“32” width=“32”>

6. 3. DTD entities
• It is a symbolic representation of information.
• Mark up elements that contains complex data
are often referred as entities.
• Entities are variables used to define shortcuts
to text and special characters.
• They are internal and external.

7. 1. Internal entity
• Refers to data that an XML processor has to
parse.
• Syntax: <!ENTITY name “entity value”>
Ex:
<?xml version=“1.0”>
<!DOCTYPE letter[
<!ENTITY hbd “happy birth day”>
]>
<letter> &hbd;</letter>

8. 2. External entity
• Used for creating a common reference
that can be shared between multiple
documents.
• There are two types: private and public
• Syntax:
<!ENTITY name SYSTEM “URL/URI”>
<!ENTITY name PUBLIC “publicID” “URI”>