DTD vs' XML Schema

1
DTD vs. XML Schema

• What is a DTD?
• Stands for Document Type Definition
• A DTD instance is a schema that describes the
  vocabulary and structures of XML files that
  conform to it
• Part of XML V1.0 Spec.

2
Why Are Schemas Valuable?

• Provide standard structures for data exchange
• Provide constraints for testing document validity

3
Why Are Schemas Valuable?

• Help manage integration of documents and data
• Framework for both document and data structures
• Help separate parts of documents for intelligent
  search/manipulation

4
What DTDs Dont Do Well

• Allow for the detailed specification of data
  types for data content
• Verify that data conforms to data type rules

5
What is XML Schema?

• Proposed new XML schema specification mechanism
  from the W3C
• Form is XML based

6
Why Use XML Schema?

• To specify data types for data content
• To verify that an XML documents data content
  conforms to its defined data types

7
DTD vs. XML Schema Ex. 1
DTD lt!ELEMENT MeasurementDetails (primaryIndex,
startIndex, endIndex, (evenSampling
unevenSampling), indexUnits, uomNamingSystem,
comment?)gt
XML Schema ltelementType name
"MeasurementDetails"gt ltsequencegt
ltelementTypeRef name "primaryIndex"/gt
ltelementTypeRef name "startIndex"/gt
ltelementTypeRef name "endIndex"/gt
ltchoicegt ltelementTypeRef name
"evenSampling"/gt
ltelementTypeRef name "unevenSampling"/gt
lt/choicegt ltelementTypeRef name
"indexUnits"/gt ltelementTypeRef name
"uomNamingSystem"/gt ltelementTypeRef name
"comment" minOccur "0" maxOccur "1"/gt
lt/sequencegt lt/elementTypegt
8
DTD vs. XML Schema Ex. 2
DTD lt!ELEMENT wellName (PCDATA)gt lt!ATTLIST
wellName type (API10 API12 API14
CPA WWN IRIS21 NPD DTI
LOCALFIELD SHORTNAME
PROJECTNAME UNKNOWN OTHER)
REQUIREDgt
XML Schema ltelementType name "wellName"gt
ltdatatypeRef name "string"/gt ltattrDecl name
"type" required "true"gt ltdatatypeRef
name "ENUMERATION"gt ltenumerationgt
ltliteralgtAPI10lt/literalgt
ltliteralgtAPI12lt/literalgt
ltliteralgtAPI14lt/literalgt
ltliteralgtCPAlt/literalgt ...
lt/enumerationgt lt/datatypeRefgt
lt/attrDeclgt lt/elementTypegt
9
Why Continue to Use DTDs?

• XML Schema is only in draft form today

10
How Can We Promote Standard Schemas?

• Register schemas with XML standards organizations
• XML.ORG (http//www.xml.org)
• Accepts DTD definitions
• BizTalk (http//www.biztalk.org)
• Accepts XML Schema definitions
• POSC plans to register WellLogML with both
  organizations

11
Where Can I Get More Information?

• http//www.posc.org/ebiz
• Check out the XML Resources and Organizations
  links
• Glance through the Glossary for a more complete
  list of XML terms