Best Practices

1
Best Practices

• XML Schemas Best Practices
• A set of guidelines for designing XML Schemas
• Created by discussions on xml-dev

2
Motivation

• XML Schemas - big ... powerful ... no experience
  base
• With anything new it is oftentimes difficult to
  know how to get started
• Purpose is to shed light on
• the design issues involved in creating a schema
• the various designs and their pros and cons

3
Whos Creating the Guidelines?

• These guidelines are being developed collectively
  by discussions among members of the xml-dev list
  group
• Participants

Ronald Bourret Jon Cleaver Rick Jelliffe Toivo
Lainevool Eric van der Vlist Sam Hunting Mike
Ripley Ed Hodder John Schlesinger
Roger Costello Curt Arnold Paul Spencer Mary
Pulvermacher Len Bullard Caroline Clewlow Eddie
Robertsson Jeff Rafter Francis Norton
Richard Lanyon Ajay Sanghi Robin Cover Tom
Passin Jonathan Borden Joe English Henry
Thompson Tim Bray Jeff Greif Caroline Weller
All are welcome to join the discussions
4
Online Summary

• For a complete summary of discussions see
  http//www.xfront.com/BestPracticesHomepage.html

5
Design Issues

• Hide or Expose?
• Design the schema to hide (localize) within the
  schema the namespaces of all the components being
  used, or design it to expose the namespaces in
  instance documents?
• Zero, One, or Many Namespaces?
• A typical project will involve the creation of
  multiple schemas. Do we design each schema to
  have the same namespace, or all different
  namespaces, or no namespace?

6
Design Issues

• Global or Local?
• Do we define our schema components globally or
  locally? What are the implications?
• Element or Type?
• Do we define our schema components as elements or
  types (i.e., complexType or simpleType)? What
  are the implications?

7
Design Issues

• Default Namespace - targetNamespace or XMLSchema?
• There are reasons why you should make the
  targetNamespace the default namespace. Learn
  why.
• Creating Variable Content Containers
• There are several approaches to creating an
  element whose content may vary. Each approach
  has its advantages and disadvantages

8
Design Issues

• Extensible Content Models
• How do we design our schemas so that instance
  documents can contain elements above and beyond
  what the schema specifies?
• Extending XML Schemas
• XML Schemas is not all powerful. What do we do
  when we have a constraint that cannot be
  expressed with XML Schemas?
• What else? (Suggestions welcome)