The document discusses schemas and their purpose in specifying the structure and constraints of an XML document. It provides examples of things that cannot be done with DTDs but can be done with schemas, such as constraining text values. The document outlines the components of a schema, including elements, attributes, and data types. It provides an example of defining a schema in IE5 and the steps involved, including declaring element types, specifying content models, and using data types.

1. Schema
 Schemas
specify the structure of an XML document
constraints on its content
 This is also the purpose of a DTD
schema does it better
syntax is XML
can use existing XML tools

2. Schema
 What you can't do with DTD's
constrain the #PCDATA e.g.
 a telephone number
 a price
 a single word
precisely constrain repetition
 up to three children on a family ticket
a precise selection of elements
 in any combination or permutation

3. Schema
 XML is a meta-language for defining tag
languages
 A schema is a formal specification (in
XML) of the grammar for one language
useful for validating content & interchange
 XML Schema is a language for writing the
specifications

4. Schemas
• Common Vocabularies
• Shared Applications
• Network effect
• Formal Sets of Rules
• Machine-based XML processing
• Not human-based document processing
• Building Contracts
• Core rules for a series of transactions

5. Schemas
• DTDs
• good at describing documents
• can't manage complex data structures
• syntax is not extensible
• available tools won't work

6. Schemas
 Schemas build on primitive types
integers, floating point, strings, dates
 Types can be based on other types
aggregations
specifications
restrictions
equivalences
 Distinction between types and elements

7. Schemas
 Schema building is very like
OO data design
E-R diagrams
 Schemas may be complex compared to
the documents
because humans 'intuitively understand' tag
names

8. Schema Standards
• XML Schema (current W3C standard)
• large, full-featured, unimplemented
• XML-Data
• early contender, supported by Microsoft
• reduced set of XML-Data is part of IE5.
• DCD
• joint creation of Microsoft and IBM
• simpler version of XML-Data

9. Schema Standards
• SOX
• XML structures via OO-inheritance
• Schematron
• uses XSLT for schemas
• DSD
• like Schematron with simpler XML syntax
• RELAX
• based on hedge automata theory
• much simpler than XML Schema

10. Schema
History

11. Schema Problems
 Legal implications of schemas as
contracts
Eskimo Snow and Scottish Rain:
Legal Considerations of Schema Design
 http://www.w3.org/TR/md-policy-design
syntactic operability with semantic fault
occurs because DTDs and schemas mix
 syntax
 semantics

12. Schema Problems
• W3C standard "XML Schemas"
• Too big, too complex
• XML 1.0 spec = 30 pages, Schemas >200
• Too much, too soon
• it isn't clear that many developers are sure
what to do with this enormous toolkit today.
• Competitors

13. Defining A Schema (IE5)
 Take an example XML document instance
<?xml version="1.0"?>
<pizzaOrder>
<when>18:04:30</when>
<cost>8.75</cost>
<pizza>Hot n Spicy</pizza>
</pizzaOrder>

14. Defining A Schema (IE5)
 First declare that it uses a schema
definition via the default namespace
<?xml version="1.0"?
xmlns="x-schema:pizzaOrderSchema.xml">
<pizzaOrder>
<when>18:04:30</when>
<cost>8.75</cost>
<pizza>Hot n Spicy</pizza>
</pizzaOrder>

15. Defining a Schema (IE5)
 Now create an outline schema
<Schema
xmlns="urn:schemas-microsoft-com:xml-data">
...
</Schema>
 ie an XML document from the schema
language namespace

16. Defining a Schema (IE5)
 First we declare the kinds of elements we
have
<Schema xmlns="urn:schemas-microsoft-com:xml-data">
<ElementType name="when"/>
<ElementType name="cost"/>
<ElementType name="pizza"/>
<ElementType name="pizzaOrder"/>
</Schema>

17. Defining a Schema (IE5)
 and specify allowable content
<Schema xmlns="urn:schemas-microsoft-com:xml-data">
<ElementType name="when" content="textOnly"/>
<ElementType name="cost" content="textOnly"/>
<ElementType name="pizza" content="textOnly"/>
<ElementType name="pizzaOrder" content="eltOnly"/>
</Schema>
textOnly, eltOnly, mixed, empty

18. Defining a Schema (IE5)
 and then content model
<Schema xmlns="urn:schemas-microsoft-com:xml-data">
<ElementType name="when" content="textOnly" />
<ElementType name="cost" content="textOnly"/>
<ElementType name="pizza" content="textOnly"/>
<ElementType name="pizzaOrder" content="eltOnly">
<element type="when"/>
<element type="cost"/>
<element type="pizza"/>
</ElementType>
</Schema>

19. Defining a Schema (IE5)
 and even the content model for text
<Schema xmlns="urn:schemas-microsoft-com:xml-data">
<ElementType name="when" content="textOnly"
type="time"/>
<ElementType name="cost" content="textOnly"
type="float"/>
<ElementType name="pizza" content="textOnly"/>
<ElementType name="pizzaOrder" content="eltOnly">
<element type="when"/>
<element type="cost"/>
<element type="pizza"/>
...

20. Defining a Schema (IE5)
 But that requires another namespace
<Schema xmlns="urn:schemas-microsoft-com:xml-data"
xmlns:dt="urn:schemas-microsoft-com:datatypes">
<ElementType name="when" content="textOnly"
dt:type="time"/>
<ElementType name="cost" content="textOnly"
dt:type="float"/>
<ElementType name="pizza" content="textOnly"/>
<ElementType name="pizzaOrder" content="eltOnly">
<element type="when"/>
<element type="cost"/>
...

21. Schema Components
 Schemas build on the declarations and
usage of elements and attributes
 ElementType elements declare a kind of element
 AttributeType elements declare a kind of attribute
 element elements show the use of an element within
the context of another element
 attribute elements show the use of an attribute on an
element

22. Schema Components
 Various attributes specify the allowable
properties each element or attribute
 model specifies whether the element may contain
'foreign' elements, not specified in the schema
 minOccurs and maxOccurs put lower- and upper-
bounds on the repetition of an element
 order specifies whether subelements must appear in
the order specified, or whether only a single
subelement can be chosen
 required states that an attribute must be present
 default gives a default value for a missing attribute

23. Schema Data Types
 Microsoft's Schema provides 23 built-in
data types to which textual content can
conform
various numeric types (float, ints)
date, time, urn, uuid, char, hex, boolean and
blob
 No derived / extended types are allowed
 Separate namespace labels data vocab

24. Using Data Types
 A node's validated data type is directly
accessible within the IE DOM
DOMelement.nodeTypedValue
instead of .nodeValue or .text
 A node's schema definition is available
DOMElement.definition property
see
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