Schema

Schemasspecify the structure of an XML documentconstraints on its content

This is also the purpose of a DTDschema does it bettersyntax is XMLcan use existing XML tools

Schema

What you can't do with DTD'sconstrain 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

Schema

XML is a meta-language for defining tag languages

A schema is a formal specification (in XML) of the grammar for one languageuseful for validating content & interchange

XML Schema is a language for writing the specifications

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

Schemas

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

Schemas

Schemas build on primitive types integers, floating point, strings, dates

Types can be based on other typesaggregationsspecificationsrestrictionsequivalences

Distinction between types and elements

Schemas

Schema building is very likeOO data designE-R diagrams

Schemas may be complex compared to the documentsbecause humans 'intuitively understand' tag

names

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

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

Schema History

Schema Problems

Legal implications of schemas as contractsEskimo Snow and Scottish Rain:

Legal Considerations of Schema Design http://www.w3.org/TR/md-policy-designsyntactic operability with semantic fault occurs because DTDs and schemas mix

syntax semantics

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

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>

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>

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

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>

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

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>

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"/> ...

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"/>...

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

Schema Components

Various attributes specify the allowable properties each element or attributemodel specifies whether the element may contain 'foreign'

elements, not specified in the schemaminOccurs 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

Schema Data Types

Microsoft's Schema provides 23 built-in data types to which textual content can conformvarious numeric types (float, ints)date, time, urn, uuid, char, hex, boolean and

blob No derived / extended types are allowed Separate namespace labels data vocab

Using Data Types

A node's validated data type is directly accessible within the IE DOMDOMelement.nodeTypedValue instead of .nodeValue or .text

A node's schema definition is availableDOMElement.definition property

seeweather

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