Introduction to XML DTD
- DTD stands for Document Type Definition.
- It is used to validate the XML documents.
- XML provides facility to create your own DTDs for XML document.
- DTD specifies the structure of the XML document.
- DTD is part of the file or separate document file.
Types of DTD
There are two types of DTDs:a) Internal DTD.
b) External DTD.
Internal DTD vs External DTD.
| Internal DTD | External DTD |
|---|---|
| Internal DTD is part of the document. | External DTD is a separate file. |
| The scope is limited to the document which is created. | It is accessible across the multiple documents. |
| Syntax: <!DOCTYPE rootelement[element and attribute declarations]> | Syntax: <!DOCTYPE rootelement|SYSTEM “path of .dtd file”> |
Components of DTD
We have to associate the .xml file with the DTD and run the same .xml file in the browser.Syntax for declaring elements in DTD:
<!ELEMENT elementname (content-type or content-model)>
Where elementname specifies the name of the element present in the xml document and content-type or content-model specifies whether the element contains textual data or other elements.
The three types of elements are as follows:
| Element type | Description | DTD Declaration |
|---|---|---|
| Empty | Contains attributes, but can't contain text or any other element. | <!Element elementname EMPTY> |
| Unrestricted | Contains text content or any other element. | <!ELEMENT elementname ANY> |
| Container | Contain another elements. | <!ELEMENT elementname (elementname, elementname [elementname])> |
Declaring Attributes in DTD
Syntax:<!!ATTLIST elementname atributename valuetype [atributetype] [“default”]>
Each attribute declaration must include at least the attribute name in a DTD as follows:
| Value Type | Description |
|---|---|
| PCDATA | Represents the plain text values. |
| ID | Assigns unique value to each element in the document. |
| (enumerated) | Assigns a specific range of values which is specified within parenthesis. |
Example : Declaring Attributes in DTD
<?xml version="1.0" encoding="UTF-8" standalone="no" ?>
<!DOCTYPE Employee
[
<!ELEMENT address (name,company,phone)>
<!ELEMENT name (#PCDATA)>
<!ELEMENT company (#PCDATA)>
<!ELEMENT phone (#PCDATA)>
]>
<address>
<name>Mayuri S</name>
<company>TutorialRide</company>
<phone>91-9800000000</phone>
</address>
