Sams Teach Yourself XML in 21 Days

By Steven Holzner

• Table of Contents
  • About the Author
  • Acknowledgments
  • We Want to Hear from You!
  • Introduction
  • Part I: At a Glance
  • Day 1. Welcome to XML
  • Day 2. Creating XML Documents
  • Day 3. Creating Well-Formed XML Documents
  • Day 4. Creating Valid XML Documents: DTDs
  • Declaring Attributes in DTDs
  • Day 6. Creating Valid XML Documents: XML Schemas
    • Using XML Schema Tools
    • Creating XML Schemas
    • Dissecting an XML Schema
    • The Built-in XML Schema Elements
    • Creating Elements and Types
    • Specifying a Number of Elements
    • Specifying Element Default Values
    • Creating Attributes
    • Summary
    • Q&A
    • Workshop
  • Day 7. Creating Types in XML Schemas
  • Part I. In Review
  • Day 8. Formatting XML by Using Cascading Style Sheets
  • Day 9. Formatting XML by Using XSLT
  • Day 10. Working with XSL Formatting Objects
  • Part II. In Review
  • Part III: At a Glance
  • Day 11. Extending HTML with XHTML
  • Day 12. Putting XHTML to Work
  • Day 13. Creating Graphics and Multimedia: SVG and SMIL
  • Day 14. Handling XLinks, XPointers, and XForms
  • Part III. In Review
  • Part IV: At a Glance
  • Day 15. Using JavaScript and XML
  • Day 16. Using Java and .NET: DOM
  • Day 17. Using Java and .NET: SAX
  • Day 18. Working with SOAP and RDF
  • Part IV. In Review
  • Part V: At a Glance
  • Day 19. Handling XML Data Binding
  • Day 20. Working with XML and Databases
  • Day 21. Handling XML in .NET
  • Part V. In Review
  • Appendix A. Quiz Answers

Creating Attributes

As with elements, with XML schemas you can specify the types of attributes. In XML documents, attribute values have to be quoted strings, and if you have, say, a number such as "100", the XML schema is able to indicate that such a number should be interpreted as an integer. To declare an attribute, you use the <xsd:attribute> element as in the following example, which declares an attribute named phone for the recordType type, which means that all elements of this type, such as <bank> in the XML document, will support this attribute:

<xsd:complexType name="recordType">
    <xsd:sequence>
        <xsd:element name="name" type="xsd:string"/>
        <xsd:element name="location" type="xsd:string"/>
        <xsd:element name="city" type="xsd:string"/>
        <xsd:element name="state" type="xsd:string"/>
    </xsd:sequence>
    <xsd:attribute name="phone" type="xsd:string"/>
</xsd:complexType>

Like <xsd:element>, <xsd:attribute> has a type attribute, and its attributes must always be of a simple type. You can also indicate whether an attribute is required or optional, or whether it has a default value. To do that, you use the <xsd:attribute> element's use and value attributes.

The use attribute specifies whether the attribute is required or optional—and if it is optional, whether the attribute's value is fixed or whether there is a default. For example, you can make the phone attribute optional like this:

<xsd:complexType name="recordType">
    <xsd:sequence>
        <xsd:element name="name" type="xsd:string"/>
        <xsd:element name="location" type="xsd:string"/>
        <xsd:element name="city" type="xsd:string"/>
        <xsd:element name="state" type="xsd:string"/>
    </xsd:sequence>
    <xsd:attribute name="phone" type="xsd:string"

           use="optional"/>
</xsd:complexType>

Here are the values you can give to the use attribute:

• default — If you don't use the use attribute, its value is the default value set with the value attribute. If you do use it, its value is the value you assign it.
• fixed — This value makes the attribute fixed. You can set its value by using the value attribute.
• optional — This value makes the attribute optional, which means the attribute may have any value.
• prohibited — This value means the attribute cannot be used.
• required — This value makes the attribute required. The attribute can have any value.

The value attribute contains a value if you need to specify one. For example, the following attribute declaration creates an attribute named year with the integer fixed value "2005":

<xsd:attribute name="year" type="xsd:int" use="fixed" value="2005">

Here's another example of an attribute declaration. This example gives the integer attribute year the default value "2005":

<xsd:attribute name="year" type="xsd:int" use="default" value="2005">

Share This