Difference between DTD and SCHEMA

DTD :

• DTD support only two data type called PCDATA and CDATA.
• DTD does not alow to describe custom datatype.
• DTD does not support XML namingspace.
• DTD document may not be an XML document.
• DTD's may be internal or external.
• You can include one DTD in xml document.

SCHEMA :

• SCHEMA support built in data type as int, long, float, doubble, String, Date etc.
• SCHEMA allow you to describe custom datatype.
• SCHEMA must support XML namingspace.
• SCHEMA document must be an XML document.
• SCHEMA must be external always.
• You can include multiple XSD's in xml document.

Difference between SAX parser and DOM parser ?

SAX Parser :

• Sax is read only parser.
• Sax follows event driven model.
• Using Sax you can read the data sequentially.
• Sax occupies very less memory because only one element information will be stored in the memory at a time.

DOM Parser :

• Dom is read write parser.
• Dom follows tree model.
• Using Dom you can read the data randomly.
• Dom occupies more memory because entire object graph and memory will be loaded in main memory at a time.