1. Document Type Definition (DTD)
IST 421
Spring 2004
Lecture 6

2. DTD Add rules to an XML document that enforce structure
Document Type Definition(DTD)
XML Schema

3. DTD
Validates a document against its model, i.e. declares what is legal
Define the elements your document can contain
Define the order in which elements appear
Require that certain elements appear
Define the allowed number of occurrences of a given element
Define the type of data an element can contain
Define child elements for a given element
Define the attributes for each of your elements
Assign constraints to the attribute values

4. DTD XML documents do not have to include a DTD
DTD becomes a way to validate a document and guarantees consistency
DTD is important when sharing an XML document with other programs
A document is valid if it conforms to a DTD
An XML document may not be valid and yet be well-formed XML code

5. Invoice without Rules <?xml version=“1.0”?> <invoice>
<merchant name>Giant Foods</merchant name>
<flower_name>Tulips</flower_name>
<ingredient_list>
<ingredient amount=“1cup”>Milk</ingredient>
<ingredient amount=“3 tsp”>Butter</ingredient>
<ingredient amount=“2 tsp”>Salt</ingredient>
<ingredient amount=“3 cloves”>Garlic</ingredient>
</ingredient_list>
</invoice>

6. Invoice with Rules <?xml version=“1.0”?> <invoice>
<merchant_name>Giant Foods</merchant_name>
<merchant_address>
<street>123 Any Street</street>
<city>Harrisburg</city>
<state>PA</state>
</merchant_address>
<sales_date> </sales_date>
<items_purchased>
<item price=“2.35” quantity=“1”>Milk</item>
<item price=“0.99” quantity=“1”>Eggs 12 count</item>
<item price=“2.65” quantity=“1”>Tropicana Orange Juice</item>
</items_purchased>
</invoice>

7. DTD There are 2 kinds of DTD declarations:
Internal DTD – provided as part of the document
External DTD – an external file
The syntax and rules for defining the 2 are the same

8. Element Declarations
If you use a DTD with your XML document, DTD must declare all elements used
Syntax for declaring an element:
<!ELEMENT element_name (content model)>

9. Element Declarations <?xml version=“1.0”? standalone=“yes”?>
<!DOCTYPE merchant_name [
<!ELEMENT merchant_name (#PCDATA)>
]>
<merchant_name>Giant Foods</merchant_name>

10. Content Models for Elements
Text <!ELEMENT item (#PCDATA)>
Supports text or character data
Elements <!ELEMENT item (element_name)>
Supports content that is another element
Mixed content <!ELEMENT item (#PCDATA, element_name)>
Supports both text and other elements #PCDATA must be first in declaration

11. Content Models for Elements
Empty <!ELEMENT item (EMPTY)>
Supports an element that has no content
Any <!ELEMENT item (ANY)>
May contain text or elements
PCDATA stands for parsed character data
Data type is not yet known

12. <?xml version=“1.0”?>
<invoice>
<merchant_name>Giant Foods</merchant_name>
<merchant_address>
<street>123 Any Street</street>
<city>Harrisburg</city>
<state>PA</state>
</merchant_address>
<sales_date> </sales_date>
<items_purchased>
<item price=“2.35” quantity=“1”>Milk</item>
<item price=“0.99” quantity=“1”>Eggs 12 count</item>
<item price=“2.65” quantity=“1”>Tropicana Orange Juice</item>
</items_purchased>
</invoice>

13. Internal DTD <?xml version=“1.0”?> <!DOCTYPE invoice[
<!ELEMENT invoice (merchant_name, merchant_address, street, city, state, sales_date, Items_purchased)>
<ELEMENT merchant_name (#PCDATA)>
<ELEMENT merchant_address (#PCDATA)>
<ELEMENT street (#PCDATA)>
<ELEMENT city (#PCDATA)>
<ELEMENT state (#PCDATA)>
<ELEMENT sales_date (#PCDATA)>
<ELEMENT items_purchased (item)>
<ELEMENT item (#PCDATA)>
<!ATTLIST item
price NMTOKEN #REQUIRED
quantity NMTOKEN #REQUIRED>
]>

14. DTD Guidelines
Special symbols to indicate how many times an element may appear.
An * indicates a unit may appear as many times as needed or not at all
An + indicates a unit must appear at least once and as many times as needed
An ? Indicates the unit can appear only once
An , indicates the elements must appear in the order specified

15. Attributes Syntax for a DTD attribute declaration
<!ATTLIST element_name
attribute_name data_type default_value
attribute_name data_type default_value >
Can be located anywhere in the DTD but it is good practice to keep it close to the corresponding element

16. Attribute Data Types CDATA ID Stands for character/string data
Contains any combination of characters except “<“ or “&”
Is simple and easy to use ID
Defined to have a value that is unique, like a key
Must start with a letter

17. Attribute Data Types IDREF NMTOKEN or NMTOKENS
Define an attribute that refers to one of the ID attributes
NMTOKEN or NMTOKENS
Data typing
NMTOKEN type attributes may not contain any white space
NMTOKENS type attributes may contain white space
May consist of letters, numbers, hyphens, periods, underscores, and colons.

18. Attribute Default Values
#REQUIRED: attribute must contain some value
#IMPLIED: attribute has no default value and may be omitted
#FIXED fixedvalue: attribute must always be set to the value, fixedvalue
Default: merely type a default value instead of the above

19. DTD Comments
Comments may be written in the DTD in the same fashion as for an XML document
<!-- This is a comment for a DTD -->

20. External DTD’s
Make sure the standalone value in the XML declaration is set to “no”
DTD declaration must tell the parser where to find the DTD file
<!DOCTYPE invoice SYSTEM “invoice.dtd”>
<!DOCTYPE invoice SYSTEM “

21. XML Schemas May 2001, W3C released XML Schema Language recommendation
Covers structure
Covers data types
Alternative to DTD’s
More powerful method to describe and set constraints on XML components

22. XML Presentation

23. Separating Content from Style
Want to display the XML information
Web browser
Print
Display of a handheld computer or Web-enabled phone
Portable Document Format (PDF)
Using XML to describe data makes it easy to create multiple presentation layouts for the same data

24. Cascading Style Sheets (CSS)
CSS style sheets contain rules and declarations that tell how to display certain elements
Style information is in an external file with a .css extension
Style Sheet Declaration
<?xml-stylesheet type=“text/css” href=“invoices.css”?>

25. Cascading Style Sheets (CSS)
CSS have 2 parts:
Element selector separated by comas
Set of properties declarations separated by a semicolon
address, city {
font-size: 12pt;
font-family: arial }

26. Cascading Style Sheets (CSS)
Comment style is different than DTD’s
/* This is a comment */

27. CSS Properties Major property categories Font properties
Text properties
Color properties
Border properties
Display properties

28. Assignment
Create a DTD for your XML document from last class – the camping gear list and run it against a validating parser.