编辑：我发现这在一篇文章，我正在读，这是什么促使我问的问题：
Why W3C XML Schema Language?
The W3C XML Schema Language is not the
only schema language. In fact,the XML
specification describes document-type
deFinitions (DTDs) as the way to
express a schema. In addition,
pre-release versions of the JAXB
Reference Implementation worked only
with DTDs — that is,not with schemas
written in the XML Schema Language.
However,the XML Schema Language is
much richer than DTDs. For example,
schemas written in the XML Schema
Language can describe structural
relationships and data types that
can’t be expressed (or can’t easily be
expressed) in DTDs. There are tools
available to convert DTDs to the W3C
XML Schema Language,so if you have
DTD-based schemas that you used with
an earlier version of the JAXB
Reference Implementation,you can use
these tools to convert the schemas to
XML Schema Language. 07000
我想我想要的例子说明为什么XML-Schema更好(如果它确实是)。
DTD’s are not namespace aware.
DTD’s have
#define,#include,and#ifdef— or,less C-oriented,the ability to define shorthand abbreviations,external
content,and some conditional parsing.A DTD describes the entire XML document (even if it leaves “holes”); a schema can define portions.
XSD has a type system.
XSD has a much richer language for describing what element or attribute content “looks like.” This is related to the type
system.
You can put a DTD inline into an XML document,you cannot do this with XSD. This means DTD’s are more secure (you only
have to protect one bytestream — the xml/dtd — and not
multiple).The official deFinition of “valid XML” requires a DTD. Since this may be impractical,if not impossible,you often have to
settle for schema-valid,which is not quite the same.
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