What is the difference between DTD and Schema (XML)

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Submitted 2009-03-24 06:26:37

What is the difference between DTD and Schema (XML)

Question:What is the difference between DTD and Schema? (XML)

Answer:The first, and probably most significant, difference between XML Schemas
and XML DTDs is that XML Schemas use XML document syntax. While
transforming the syntax to XML doesn’t automatically improve the quality
of the description, it does make those descriptions far more extensible
than they were in the original DTD syntax. Declarations can have richer
and more complex internal structures than declarations in DTDs, and
schema designers can take advantage of XML’s containment hierarchies to
add extra information where appropriate - even sophisticated information
like documentation. There are a few other benefits from this approach.
XML Schemas can be stored along with other XML documents in XMLoriented
data stores, referenced, and even styled,
using tools like XLink, XPointer, and XSL.
The largest addition XML Schemas provide to the functionality of the
descriptions is a vastly improved data typing system. XML Schemas
provide data-oriented data types in addition to the more documentoriented
data types XML 1.0 DTDs support, making XML more suitable for
data interchange applications.
Built-in datatypes include strings, booleans, and time values, and the XML
Schemas draft provides a mechanism for generating additional data types.
Using that system, the draft provides support for all of the XML 1.0 data
types (NMTOKENS, IDREFS, etc.) as well as data-specific types like
decimal,integer, date, and time. Using XML Schemas, developers can build
their own libraries of easily interchanged data types and use them inside
schemas or across multiple schemas.
The current draft of XML Schemas also uses a very different style for
declaring elements and attributes to DTDs. In addition to declaring
elements and attributes individually, developers can create models -
archetypes - that can be applied to multiple elements and refined if
necessary. This provides a lot of the functionality SOX had developed to
support object-oriented concepts like inheritance. Archetype development
and refinement will probably become the mark of the high-end schema
developer, much as the effective use of parameter entities was the mark of
the high-end DTD developer. Archetypes should be easier to model and
use consistently, however.
XML Schemas also support namespaces, a key feature of the W3C’s vision
for the future of XML. While it probably wouldn’t be impossible to integrate
DTDs and namespaces, the W3C has decided to move on, supporting
namespaces in its newer developments and not retrofitting XML 1.0. In
many cases, provided that namespace-prefixes don’t change or simply
aren’t used, DTD’s can work just fine with namespaces, and should be able
to interoperate with namespaces and schema processing that relies on
namespaces. There will be a few cases, however, where namespaces may
force developers to use the newer schemas rather than the older DTDs.

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Question Popularity: Submitted 2009-03-24 06:26:37

Question Popularity:
Submitted 2009-03-24 06:26:37