1. Session III Chapter 6 – Creating DTDs http://www.profburnett.com
CMP 051 XML Introduction
Session III
Chapter 6 – Creating DTDs

2. Outline Introduction DTD Declaration Syntax DTD XML Building Blocks
The Need for DTDs
DTD Features
DTD Schematic
DTD Declaration Syntax
DTD XML Building Blocks
DTD Elements
DTD Attributes
8/1/2014
Copyright © Carl M. Burnett

3. Introduction Creates rules and structures for XML vocabulary
Document Type Definitions (DTDs) and XML schemas are vehicles for document modeling
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Copyright © Carl M. Burnett

4. The Need for DTDs Default attribute values Handling of white space
Part of the declaration (DTD or schema portion) must be processed
To obtain correct default values
Handling of white space
Without the DTD, there is no way for the processor to distinguish between element content and mixed content
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Copyright © Carl M. Burnett

5. The Need for DTDs Authoring environments Authoring methods
Process the document type declarations for authors
To comply with the content models of the document
Authoring methods
DTD is required for any structure to be created, understood, and maintained
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Copyright © Carl M. Burnett

6. DTD Features Declares a set of allowed elements
DTD forms the vocabulary of the language
Defines the content model for each element
Content model indicates
What elements can be nested within other elements
The order in which elements appear
How many elements are allowed
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Copyright © Carl M. Burnett

7. DTD Features
Declares a set of allowed attributes for each of its elements
Attributes defines the name, datatype, default values and behavior
Includes other mechanisms
Entity declarations
Notation declarations
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Copyright © Carl M. Burnett

8. Document Type Definition
Basic DTD Schematic
Document Type Definition
Prolog (optional)
Element Declarations
Attribute List Declarations
Entity Declarations
Notation Declarations
Other Content
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Copyright © Carl M. Burnett

9. DTD Declaration Syntax
Declaration Identifier
<!ELEMENT elementname content-model>
Start Indicator
End Indicator
Reserved Keyword (Upper Case Only)
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10. DTD - XML Building Blocks
All XML documents and HTML documents) have the following building blocks:
Elements
Attributes
Entities
PCDATA
CDATA
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Copyright © Carl M. Burnett

11. DTD Elements Element type declarations
Specify the names of elements and nature of their content
Define only one element
DTD must contain as many element declarations as there are elements
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Copyright © Carl M. Burnett

12. Element declaration syntax
Valid XML Name (begins with a letter, colon, or underscore)
<!ELEMENT elementname content-model>
Start Indicator
Content Model
(also called content
Specification)
End Indicator
Reserved Keyword (Upper Case Only)
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Copyright © Carl M. Burnett

13. XML Naming Conventions
Element names
Can start with a letter, a colon, or an underscore (no numbers)
Rest of the name can be alphanumeric, underscores, hyphens, colons and periods
Can not contain reserved characters: ampersand (&), at symbol or less than symbol (<)
Can not contain white space or use parentheses (), or brackets []
11/9/2018
Copyright © Carl M. Burnett

14. Elements with Text - Parsed Character Data only (PCDATA)
Many Elements will only contain text.
Use reserved keyword/symbol combination #PCDATA
Parser checks the entity references
Replaces the reference with actual entity values.
<ELEMENT name (#PCDATA)>
<!ELEMENT location (#PCDATA)>
<!ELEMENT height (#PCDATA)>
<!ELEMENT year_built (#PCDATA)>
<!ELEMENT year_destroyed (#PCDATA)>
<!ELEMENT how_destroyed (#PCDATA)>
<!ELEMENT story (#PCDATA)>
1. Type <!ELEMENT TAG to DEFEINE tag.
2. Type (#PCDATA) to define the tag that contains a text value.
3. Type > to close out the Element definition.
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Copyright © Carl M. Burnett

15. Element with Empty Element
1. Type <!ELEMENT TAG to DEFEINE tag.
2. Type EMPTY to define the tag that contains an empty value.
<!ELEMENT main_image EMPTY>
<!ELEMENT source EMPTY>
<!ELEMENT name (#PCDATA)>
<!ELEMENT location (#PCDATA)>
<!ELEMENT height (#PCDATA)>
<!ELEMENT year_built (#PCDATA)>
<!ELEMENT year_destroyed (#PCDATA)>
<!ELEMENT how_destroyed (#PCDATA)>
<!ELEMENT story (#PCDATA)>
3. Type > to close out the Element definition.
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Copyright © Carl M. Burnett

16. Element that Contain Children Elements
Elements can be parent elements with child elements.
<!ELEMENT wonder
(name, location, height)>
<!ELEMENT name (#PCDATA)>
<!ELEMENT location (#PCDATA)>
<!ELEMENT height (#PCDATA)>
1. Type <!ELEMENT TAG to DEFEINE tag.
2. Type (child1, child2)to define the children elements.
3. Type > to close out the Element definition.
Then define the Children elements.
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Copyright © Carl M. Burnett

17. Elements with Choices Contain both data and child elements
#PCDATA must be specified within the parentheses (declares the element may contain parseable data)
Separate child elements with vertical line (| known as the pipe)
<!ELEMENT ancient_wonders (wonder+)>
<!ELEMENT wonder (#PCDATA | name | location | city | country)*>
<!ELEMENT name (#PCDATA)>
<!ELEMENT location (#PCDATA)>
<!ELEMENT city (#PCDATA)>
<!ELEMENT country (#PCDATA)>
1. Type <!ELEMENT TAG to DEFEINE tag.
* Is a qualifier to allow elements to have a number of choices.
2. Type (#PCDATA | child1 | child2 | child3) to define the children elements.
3. Type > to close out the Element definition.
Then define the Children elements.
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Copyright © Carl M. Burnett

18. Elements with No Content Restrictions
Elements with any content must use reserved keyword ANY.
XML validator does not have to perform a check on the specified element’s content.
<!ELEMENT ancient_wonders (wonder+)>
<!ELEMENT wonder (#PCDATA | name | location | city | country)*>
<!ELEMENT name (#PCDATA)>
<!ELEMENT location ANY>
<!ELEMENT city (#PCDATA)>
<!ELEMENT country (#PCDATA)>
1. Type <!ELEMENT TAG to DEFEINE tag.
2. Type ANY to define the type of element.
3. Type > to close out the Element definition.
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Copyright © Carl M. Burnett

19. Operators Used with Element Content
Comma (,) specifies a required sequence of child elements
Vertical line, or “pipe”, ( | ) specifies a list of candidate child elements
Question mark (?) specifies that the child element is optional
Plus Sign (+) specifies that at least one child element(s) is required
Asterisk (*) specifies that zero or more of the child element(s) may appear
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Copyright © Carl M. Burnett

20. DTD Attributes
In a DTD, attributes are declared with an ATTLIST declaration.
In XML, there are no rules about when to use attributes, and when to use child elements.
Avoid using attributes?
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21. Avoid Using Attributes?
Some of the problems with attributes are:
attributes cannot contain multiple values (child elements can)
attributes are not easily expandable (for future changes)
attributes cannot describe structures (child elements can)
attributes are more difficult to manipulate by program code
attribute values are not easy to test against a DTD
If you use attributes as containers for data, you end up with documents that are difficult to read and maintain.
Try to use elements to describe data.
Use attributes only to provide information that is not relevant to the data.
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Copyright © Carl M. Burnett

22. An Exception to Attribute Rule
Sometimes you can assign ID references to elements.
These ID references can be used to access XML elements in much the same way as the NAME or ID attributes in HTML.
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Copyright © Carl M. Burnett

23. Defining Attributes Attribute Definition consist of four parts:
Elements Name
Attribute Name
Attribute Type
Optional Status
<!ELEMENT height (#PCDATA)>
<!ATTLIST height units CDATA #REQUIRED>
1. Type <!ATTLIST tag where the tag is element name.
2. Type att_name where att_name is name of the attribute.
3. Type CDATA wto indicate the attribute type is text.
4. Type #IMPLIED or #REQUIRED for the optional status.
The #IMPLIED can be omitted if desired.
5. Type > to close out the attribute definition.
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Copyright © Carl M. Burnett

24. Defining Attribute Default Values
<!ELEMENT height (#PCDATA)>
<!ATTLIST height units CDATA “Default_Value”>
You cannot combine the use of optional status of #IMPLIED or #REQUIRED if you provide a default value for the attribute.
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Copyright © Carl M. Burnett

25. Defining Attribute with Choices
1. Type <!ATTLIST tag where the tag is element name.
<!ELEMENT height (#PCDATA)>
<!ATTLIST height
units (inches|feet) #REQUIRED>
2. Type att_name where att_name is name of the attribute.
3. Type (choice1 | choice2) where choice represents the
possible value for the attribute choice.
4. Type #IMPLIED or #REQUIRED for the optional status.
The #IMPLIED can be omitted if desired.
5. Type > to close out the attribute definition.
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Copyright © Carl M. Burnett

26. Defining Attributes with Unique Values
1. Type <!ATTLIST tag where the tag is element name.
<!ELEMENT wonder (name)>
<!ATTLIST wonder
code ID #REQUIRED>
2. Type att_name where att_name is name of the attribute.
3. Type ID to define value of the attribute.
4. Type #IMPLIED or #REQUIRED for the optional status.
The #IMPLIED can be omitted if desired.
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Copyright © Carl M. Burnett

27. Referencing Attributes with Unique Values
1. Type <!ATTLIST tag where the tag is element name.
<!ELEMENT special_site (title, url)>
<!ATTLIST special_site
wonder_focus IDREF #REQUIRED>
2. Type att_name where att_name is name of the attribute.
3. Type IDREF hto define attribute that contains a value
matching an existing ID value.
4. You can also type IDREFS that can contains several values
separated with white spaces.
<!ELEMENT general_site (title, url)>
<!ATTLIST general_site
contents IDREFS #REQUIRED>
5. Type #IMPLIED or #REQUIRED for the optional status.
The #IMPLIED can be omitted if desired.
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Copyright © Carl M. Burnett

28. Restricting Attributes to Valid XML Names
1. Type <!ATTLIST tag where the tag is element name.
<wonder>
<w_visit
primary_keyword="colossus"/>
<name language="English">
Colossus of Rhodes</name>
. . .
primary_keyword="great pyramid"/>
Great Pyramid of Giza</name>
2. Type att_name where att_name is name of the attribute.
3. Type NMTOKEN if you want the attribute value to be a valid
XML name.
4. You can also type NMTOKENS if you want the attribute value to
be a valid XML name based on a separated liste with white spaces.
5. Type #IMPLIED or #REQUIRED for the optional status.
The #IMPLIED can be omitted if desired.
8/1/2014
Copyright © Carl M. Burnett

29. Chapter 7 - Entities and Notations in DTDs
Review
Introduction
The Need for DTDs
DTD Features
DTD Schematic
DTD Declaration Syntax
DTD XML Building Blocks
DTD Elements
DTD Attributes
Next:
Chapter 7 - Entities and Notations in DTDs
8/1/2014
Copyright © Carl M. Burnett