Web 310XML Schema : What You Need to Know and Why

Yasser ShohoudProgram ManagerXML MessagingMicrosoft Corporation

Agenda

Understand what XML Schema is and how it is used by ASMX Web services

Learn to create XML Schemas using Visual Studio

Understand some XML Schema gotchas and best practices

XML Schema and WSDLWhy Care About XML Schema?

WSDL describes Web Service end pointsSpecifies operations performed by an endpoint

Specifies messages understood by the end point

Specifies message types using XML Schema

What is XML Schema?

Basis of strongly typed XMLXML Serialization – ASP.NET Web Services

DataSet

SQLXML

XQuery

Contract between producer and consumer of XML

ASP.NET Web Methods

Regular methods with [WebMethod] attribute

Parameters are CLR objects Return types are CLR objects

[WebMethod] public int Add (int x, int y) { return x + y; }

Transmitted and received on the wire as XML

ASP.NET Web MethodsUnder the Covers

Strongly Typed XML Mapped to ObjectsXML Schema is basis of mapping

Validating with XML Schema

Use XmlValidatingReaderAdd the XML schema to its schemas collection

Validates as you read

Upon errorAbort validation

Can continue validation if given a ValidationEventHandler

Example …

Agenda

Understand what XML Schema is and how it is used by ASMX Web services

Learn to create XML Schemas using Visual Studio

Understand some XML Schema gotchas and best practices

Schema Basics

XML Schema lets you declare elementsThese elements appear in XML documents (instance documents)

Each element has a typeChoose from over 40 built-in types

Or define your own types

Defining your own typesSimple types: Does not contain elements or attributes

Complex types: Contains elements and/or attributes

Example

Creating an Order schema

Creating classes from schema

Creating schema from classes

Agenda

Understand what XML Schema is and how it is used by ASMX Web services

Learn to create XML Schemas using Visual Studio

Understand some XML Schema gotchas and best practices

Beware: Contract not enforced

Message Contract Described by XML Schema

XmlSerializer does not Enforce the Contract

Sequences not enforced

Ignores unexpected elements

Inserts defaults for missing elements

Identity constraints not enforced

Simple type restrictions not checked

Enforcing the ContractHaving your cake and eating it

Use XmlElement parameters and XmlValidatingReader

Use a SoapExtension that uses XmlValidatingReader at BeforeDeserialize stage

But you need to know the best practices

XML Schema Best Practices Favor the basic simple types

Basic typesxs:string

xs:int / xs:integer / xs:double / xs:float

xs:date / xs:time

Esoteric typesxs:ENTITIES / xs:NOTATION

xs:gMonth, xs:gMonthDay

xs:unsignedByte

XML Schema Best Practices Use simple type restriction

Facets enable stronger contractsEnforce input size (xs:length)

Enforce input value range (xs:minInclusive, etc)

Enforce input contents (xs:pattern)

Restrictions to avoidxs:pattern on non-string types

Examples …

XML Schema Best Practices elementFormDefault=“qualified”

<!-- using a schema with elementFormDefault=‘qualified’ makes all elements qualified (not just top-level ones) --><n:Person xmlns:n="http://demos.teched.com/schemas"> <n:FirstName>John</n:FirstName> <n:LastName>Smith</n:LastName></n:Person>

<!-- using a schema with elementFormDefault=‘qualified’ makes all elements qualified (not just top-level ones) --><n:Person xmlns:n="http://demos.teched.com/schemas"> <n:FirstName>John</n:FirstName> <n:LastName>Smith</n:LastName></n:Person>

<xs:schema id="SchemaEx1" elementFormDefault="qualified"targetNamespace="http://demos.teched.com/schemas" xmlns="http://demos.teched.com/schemas" xmlns:mstns="http://demos.teched.com/schemas" xmlns:xs="http://www.w3.org/2001/XMLSchema"> <xs:element name="Person"> <xs:complexType> <xs:sequence> <xs:element name="FirstName" type="xs:string" /> <xs:element name="LastName" type="xs:string" /> </xs:sequence> </xs:complexType> </xs:element></xs:schema>

<xs:schema id="SchemaEx1" elementFormDefault="qualified"targetNamespace="http://demos.teched.com/schemas" xmlns="http://demos.teched.com/schemas" xmlns:mstns="http://demos.teched.com/schemas" xmlns:xs="http://www.w3.org/2001/XMLSchema"> <xs:element name="Person"> <xs:complexType> <xs:sequence> <xs:element name="FirstName" type="xs:string" /> <xs:element name="LastName" type="xs:string" /> </xs:sequence> </xs:complexType> </xs:element></xs:schema>

Without elementFormDefault

<n:Person xmlns:n="http://demos.teched.com/schemas"> <FirstName>John</FirstName> <LastName>Smith</LastName></n:Person>

<n:Person xmlns:n="http://demos.teched.com/schemas"> <FirstName>John</FirstName> <LastName>Smith</LastName></n:Person>

<xs:schema id="SchemaEx1" targetNamespace="http://demos.teched.com/schemas" xmlns="http://demos.teched.com/schemas" xmlns:mstns="http://demos.teched.com/schemas" xmlns:xs="http://www.w3.org/2001/XMLSchema"> <xs:element name="Person"> <xs:complexType> <xs:sequence> <xs:element name="FirstName" type="xs:string" /> <xs:element name="LastName" type="xs:string" /> </xs:sequence> </xs:complexType> </xs:element></xs:schema>

<xs:schema id="SchemaEx1" targetNamespace="http://demos.teched.com/schemas" xmlns="http://demos.teched.com/schemas" xmlns:mstns="http://demos.teched.com/schemas" xmlns:xs="http://www.w3.org/2001/XMLSchema"> <xs:element name="Person"> <xs:complexType> <xs:sequence> <xs:element name="FirstName" type="xs:string" /> <xs:element name="LastName" type="xs:string" /> </xs:sequence> </xs:complexType> </xs:element></xs:schema>

XML Schema Best Practices Global elements over global types

Global schema components can be reused by other schemas

Model groups and complex types are content models

Prefer exposing named elements and attributes

{ element ns:name {xs:string} } of type P

ns:person { element ns:name {xs:string}}

XML Schema Best Practices Groups vs. Complex types

What is a complex type?xs:group + xs:attributeGroup + type derivation

Use groups if content model not reused

Groups are externally visible, anonymous complex types are not

XML Schema Best Practices Extensibility and Open Content

Use wildcards to enable extensibility in your messages

xs:anyxs:anyAttribute

Typical gotchas with wildcards ##other processContents = “lax” Non-deterministic schema

This is key for extensibility and versioning!

XML Schema Best Practices Identity Constraints

Prefer key/keyref/unique to id/idref

Drawbacks of id/idrefWorks only on string types

Not scoped

Limitations on values

XML Schema Best Practices Versioning Schemas

Message formats should have a version attribute

Incremental, backwards compatible changes

Increase version number

Significant, backwards incompatible changes

Change namespace name

Summary

XML Schemas are used to define your data structures

Document and message format

The basis of Web services contracts

You can use Visual Studio to design your schemas

Whatever tool you use, apply best practices

Open content model is key for versioning

Keep it simple for interop

ResourcesResourcesOnline resources

microsoft.public.dotnet.xml

microsoft.public.dotnet.framework.webservices

http://www.msdn.com/columns/xml.asp

Real World XML Web ServicesAddison Wesley, 2003

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Appendix…Appendix…• Information on using XmlElement

parameters and XmlValidatingReader available at http://msdn.microsoft.com/library/en-us/dnservice/html/service04162003.asp

• Information on SoapExtension class at http://msdn.microsoft.com/library/en-us/cpref/html/frlrfSystemWebServicesProtocolsSoapExtensionClassTopic.htm

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© 2003 Microsoft Corporation. All rights reserved.© 2003 Microsoft Corporation. All rights reserved.This presentation is for informational purposes only. MICROSOFT MAKES NO WARRANTIES, EXPRESS OR IMPLIED, IN THIS SUMMARY.This presentation is for informational purposes only. MICROSOFT MAKES NO WARRANTIES, EXPRESS OR IMPLIED, IN THIS SUMMARY.