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A Complex Web - XML

Imagine a technology that offered you all the power of a DTD without the associated unpleasantness of those strange symbols and arcane commands. Sounds too good to be true? Say hello to XML Schema.

  1. Understanding XML Schema
  2. The Next Generation
  3. An Evening At The Moulin Rouge
  4. Simple Simon
  5. A Complex Web
  6. Nesting Season
  7. Battle Of The Sexes
  8. Dealing With The Ref
  9. Different Flavours
  10. When In Rome...
  11. Test Drive
  12. The Next Step
By: Harish Kamath, (c) Melonfire
Rating: starstarstarstarstar / 3
October 15, 2001

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Let's now look at a complex element, as illustrated by the following XML snippet

<movie> <title>Moulin Rouge</title> <director>Baz Luhrmann</director> </movie>
As stated above, complex elements can contain other (simple or complex) elements, and may also possess additional attributes. Corresponding to this, complex element definitions within a schema can contain definitions for other (simple or complex) elements, definitions for element attributes (if any), and references to other element definitions within the schema (more on this later).

When defining complex types, there are again two ways in which the definition can be structured. The first involves defining a complex type, giving it a name, and then using this newly-minted type in a regular <xsd:element> declaration.

<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema"> <!-- define a new datatype for a complex element --> <xsd:complexType name="complexDType"> <xsd:sequence> <xsd:element name="title" type="xsd:string"/> <xsd:element name="director" type="xsd:string"/> </xsd:sequence> </xsd:complexType> <!-- create an element of this type --> <xsd:element name="movie" type="complexDType" /> </xsd:schema>
The second option involves combining the two steps above into a single step - the definition of the complex element is embedded within the <xsd:element> declaration itself.

Here's how the XML snippet above would be represented in a schema.

<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema"> <xsd:element name="movie"> <!-- this complex element definition has no name, and is referred to as an "anonymous" element --> <xsd:complexType> <xsd:sequence> <xsd:element name="title" type="xsd:string"/> <xsd:element name="director" type="xsd:string"/> </xsd:sequence> </xsd:complexType> </xsd:element> </xsd:schema>
The advantage of creating a named type should be obvious - the new type, once defined, can be used in multiple places within the schema simply by referencing it by name. The following example illustrates this:

<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema"> <!-- define a new datatype --> <xsd:simpleType name="simpleDType"> <xsd:restriction base="xsd:integer"> <!-- restrict integer values between 1 and 10 --> <xsd:minInclusive value="1"/> <xsd:maxInclusive value="10"/> </xsd:restriction> </xsd:simpleType> <xsd:element name="movie"> <!-- this complex element definition has no name, and is referred to as an "anonymous" element --> <xsd:complexType> <xsd:sequence> <!-- simple elements using built-in types --> <xsd:element name="title" type="xsd:string"/> <xsd:element name="director" type="xsd:string"/> <!-- simple element using new derived type --> <xsd:element name="rating" type="simpleDType"/> </xsd:sequence> </xsd:complexType> </xsd:element> </xsd:schema>

>>> More XML Articles          >>> More By Harish Kamath, (c) Melonfire

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