1. XML
Outline 1 XML 2 DTD

2. The xml doc ends with the closing tag of the root element.
Lines 1-5 comprise the Prolog. Line 1 is the XML declaration. “version” & “encoding” are attributes.
1 <?xml version="1.0" encoding="ISO "?> 2
3 <!DOCTYPE web-app
4 PUBLIC "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
5 " "> 6
7 <web-app> 8
<!-- Servlet definitions -->
<servlet>
<servlet-name>welcome</servlet-name>
<servlet-class>WelcomeServlet</servlet-class>
</servlet> 14
<!-- Servlet mappings -->
<servlet-mapping>
<servlet-name>welcome</servlet-name>
<url-pattern>/welcome</url-pattern>
</servlet-mapping> 20
21 </web-app>
Document Type Definition. Either a DTD or Schema is used by a parser to validate the xml doc.
The Body of the xml doc starts with the root element. An element consists of a start tag, an end tag & everything in between.
A comment.
<servlet> is a child of the <web-app> element and a parent to <servlet-name> & <servlet-class>. Well-formed xml docs follow a strict parent-child hierarchy.
The xml doc ends with the closing tag of the root element.

3. <. DOCTYPE web-app PUBLIC "-//Sun Microsystems, Inc
<!DOCTYPE web-app PUBLIC "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN" "
DOCTYPE refers to web-app, the root element – this is the definition for this web-app document
PUBLIC means the DTD is available on the Internet. Locally-stored DTDs would instead use the SYSTEM keyword, followed by the local path, e.g., “C:\Windows\Desktop\web-app_2_3.dtd”
"-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN“ is the “Formal Public Identifier” used with PUBLIC DTDs
The dash ( - ) indicates the DTD has not been approved by a Standards body, such as ISO. Approved Standard DTDs use a plus sign here ( + ).
Sun Microsystems, Inc. is the name of the owner who maintains the DTD.
DTD is the document type and Web Application 2.3 is a label that describes the document.
EN is the two-letter abbreviation for the language the DTD is written in. Here, it’s English.
“ specifies the URL where the parser may find a copy of the DTD. Let’s take a look at this DTD.