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
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>
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
weather
.html
