DTD

This slide contain all the information regarding DTD and its implementation

1. DTD

2. Introduction S tands for Document Type Definition Allows to create rules for the elements within your XML documents So, for an XML document to be well-formed, it needs to use correct XML syntax, and it needs to conform to its DTD or schema I s declared at the top of your XML document The actual contents of the DTD can be included within your XML document or included in another . dtd document

3. Example DTD

4. DTD <!DOCTYPE> DTD can either be internal (written into the same document that it's being used in) external (located in another document ). DTD is declared at the top of your XML document using the !DOCTYPE declaration. The basic syntax is:

5. DTD Variations <!DOCTYPE rootname [DTD]>

6. <!DOCTYPE rootname SYSTEM URL> The keyword SYSTEM indicates that it's a private DTD (not for public distribution ) DTD is defined in a document located at the URL

7. <!DOCTYPE rootname SYSTEM URL [DTD]> The keyword SYSTEM indicates that it's a private DTD (not for public distribution ) The presence of URL and [DTD] together indicates that this is both an external and internal DTD (part of the DTD is defined in a document located at the URL, the other part is defined within the XML document )

8. Example

9. Internal DTD Whether we use an external or internal DTD, the actual syntax for the DTD is the same Same code could just as easily be part of an internal DTD or an external one The only difference between internal and external is in the way it's declared with DOCTYPE

10. Example

11. External DTD I s one that resides in a separate document To use the external DTD, we need to link to it from our XML document by providing the URI of the DTD file This URI is in the form of a URL The URL can point to a local file using a relative reference, or a remote one ( eg , using HTTP )

12. Example

13. Combined DTD C an use both an internal DTD and an external one at the same time This could be useful if you need to adhere to a common DTD, but also need to define your own definitions locally

14. Example

15. DTD Elements Creating a DTD is quite straight forward To define an element in your DTD, we use the <!ELEMENT> declaration The actual contents of your <!ELEMENT> declaration will depend on the syntax rules you need to apply to your element

16. Basic Syntax <!ELEMENT element_name content_model > element_name is the name of the element c ontent_model could indicate a specific rule, data or another element If it specifies a rule, it will be set to either ANY or EMPTY If specifies data or another element, the data type/element name needs to be surrounded by brackets (i.e. (tutorial) or (#PCDATA ))

17. Plain Text If an element should contain plain text, you define the element using #PCDATA. PCDATA stands for Parsed Character Data Syntax : <!ELEMENT element_name (#PCDATA)> Example : <!ELEMENT name (#PCDATA)> The above line in your DTD allows the name element to contain non-markup data in your XML document : <name>XML Tutorial</name>

18. Unrestricted Elements If it doesn't matter what element contains, we can create an element using the content_model of ANY D oing this removes all syntax checking, so we should avoid using this if possible Syntax : <!ELEMENT element_name ANY> Example : <!ELEMENT tutorials ANY>

19. Empty Elements E mpty element is one without a closing tag. For example, in HTML , the < br /> and < img /> tags are empty elements. Here's how you define an empty element : Syntax : <!ELEMENT element_name EMPTY> Example : <!ELEMENT header EMPTY> The above line in your DTD defines the following empty element for your XML document : <header />

20. Child Elements C an specify that an element must contain another element, by providing the name of the element it must contain. Here's how you do that : Syntax : <!ELEMENT element_name ( child_element_name )> Example : <!ELEMENT tutorials (tutorial )>

21. The above line in DTD allows the tutorials element to contain one instance of the tutorial element in XML document :

22. Multiple Child Elements (Sequences ) You can also provide a comma separated list of elements if it needs to contain more than one element. This is referred to as a sequence. The XML document must contain the tags in the same order that they're specified in the sequence . Syntax : <! ELEMENT element_name ( child_element_name , child_element_name ,...)> Example : <! ELEMENT tutorial (name, author)>

23. The above line in DTD allows the tutorial element to contain one instance of the name element and one instance of the author element in XML document :

24. DTD Element Operators Are used to specify the number the times the child elements can be used inside parents elements

25. Zero or More To allow zero or more of the same child element, use an asterisk (*) Syntax : <! ELEMENT element_name ( child_element_name *)> Example : <! ELEMENT tutorials (tutorial*)>

26. One or More To allow one or more of the same child element, use a plus sign (+): Syntax : <! ELEMENT element_name ( child_element_name +)> Example : <! ELEMENT tutorials (tutorial+)>

27. Zero or One To allow either zero or one of the same child element, use a question mark (?): Syntax : <! ELEMENT element_name ( child_element_name ?)> Example : <! ELEMENT tutorials (tutorial?)>

28. Choices C an define a choice between one or another element by using the pipe (|) operator . Syntax: <!ELEMENT element_name (choice_1 | choice_2 | choice_3 )> For example, if the tutorial element requires a child called either name, title, or subject (but only one of these) <! ELEMENT tutorial (name | title | subject)>

29. DTD Operators with Sequences C an apply any of the DTD operators to a sequence : Syntax : <! ELEMENT element_name ( child_element_name dtd_operator , child_element_name dtd_operator ,...)> Example : <! ELEMENT tutorial (name+, author?)>

30. DTD Attributes Just as we need to define all elements in your DTD, we also need to define any attributes they use . U se the <!ATTLIST> declaration to define attributes S ingle <!ATTLIST> declaration to declare all attributes for a given element

31. Syntax Example

32. DTD Attribute Default Values