A Brief Review of XML Schemas

A Brief Review of XML Schemas

To get an idea of how these various other schema definition languages might appear for an XML document, let’s go back to our online grocery store sample XML document from Chapter 4, “Creating XML Schemas,” which is shown in Listing 6.1.

LISTING 6.1 PurchaseOrder.xml Provides a Sample XML Document for an Online Grocery Store Order

<PurchaseOrder  Tax=”5.76”  Total=”75.77”>

<ShippingInformation> <Name>Dillon Larsen</Name> <Address>

<Street>123  Jones  Rd.</Street>

<City>Houston</City>

<State>TX</State>

<Zip>77381</Zip>

</Address>

<Method>USPS</Method> <DeliveryDate>2001-08-12</DeliveryDate>

</ShippingInformation>

<BillingInformation> <Name>Madi Larsen</Name> <Address>

<Street>123 Jones Rd.</Street> <City>Houston</City> <State>TX</State> <Zip>77381</Zip>

</Address>

<PaymentMethod>Credit Card</PaymentMethod> <BillingDate>2001-08-09</BillingDate>

</BillingInformation>

<Order  SubTotal=”70.01”  ItemsSold=”17”>

<Product  Name=”Baby  Swiss”  Id=”702890”  Price=”2.89”

➥ Quantity=”1”/>

<Product  Name=”Hard  Salami”  Id=”302340”  Price=”2.34”

➥ Quantity=”1”/>

<Product  Name=”Turkey”  Id=”905800”  Price=”5.80”

➥ Quantity=”1”/>

<Product  Name=”Caesar  Salad”  Id=”991687”  Price=”2.38”

➥ Quantity=”2”/>

<Product  Name=”Chicken  Strips”  Id=”133382”  Price=”2.50”

➥ Quantity=”1”/>

<Product  Name=”Bread”  Id=”298678”  Price=”1.08”

➥ Quantity=”1”/>

<Product  Name=”Rolls”  Id=”002399”  Price=”2.24”

➥ Quantity=”1”/>

<Product  Name=”Cereal”  Id=”066510”  Price=”2.18”

➥ Quantity=”1”/>

<Product  Name=”Jalapenos”  Id=”101005”  Price=”1.97”

➥ Quantity=”1”/>

<Product  Name=”Tuna”  Id=”000118”  Price=”0.92”

➥ Quantity=”3”/>

<Product  Name=”Mayonnaise”  Id=”126860”  Price=”1.98”

➥ Quantity=”1”/>

<Product  Name=”Top  Sirloin”  Id=”290502”  Price=”9.97”

➥ Quantity=”2”/>

<Product  Name=”Soup”  Id=”001254”  Price=”1.33”

➥ Quantity=”1”/>

<Product  Name=”Granola  Bar”  Id=”026460”  Price=”2.14”

➥ Quantity=”2”/>

<Product  Name=”Chocolate  Milk”  Id=”024620”  Price=”1.58”

➥ Quantity=”2”/>

<Product  Name=”Spaghetti”  Id=”000265”  Price=”1.98”

➥ Quantity=”1”/>

<Product  Name=”Laundry  Detergent”  Id=”148202”  Price=”8.82”

➥ Quantity=”1”/> </Order>

</PurchaseOrder>

As you can see, Listing 6.1 represents a fairly small and simple order that could be placed online. It contains the information necessary regarding how payment is to be made, how the order is to be shipped, and what day delivery should be. For comparison purposes with the other schema formats discussed in the rest of this chapter, we’ll also include the W3C schema for our sample XML document, as shown in Listing 6.2.

LISTING 6.2 PurchaseOrder.xsd Contains a W3C Schema for PurchaseOrder.xml

<xsd:schema  xmlns:xsd=”http://www.w3.org/2001/XMLSchema”>

<xsd:annotation>

<xsd:documentation>

Purchase Order schema for an online grocery store. </xsd:documentation>

</xsd:annotation>

<xsd:element  name=”PurchaseOrder”  type=”PurchaseOrderType”/>

<xsd:complexType name=”PurchaseOrderType”> <xsd:all>

<xsd:element name=”ShippingInformation” type=”InfoType” ➥ minOccurs=”1” maxOccurs=”1”/>

<xsd:element name=”BillingInformation” type=”InfoType” ➥ minOccurs=”1” maxOccurs=”1”/>

<xsd:element name=”Order” type=”OrderType” ➥ minOccurs=”1” maxOccurs=”1”/>

</xsd:all>

<xsd:attribute name=”Tax”> <xsd:simpleType>

<xsd:restriction base=”xsd:decimal”> <xsd:fractionDigits value=”2”/>

</xsd:restriction>

</xsd:simpleType>

</xsd:attribute> <xsd:attribute name=”Total”>

<xsd:simpleType>

<xsd:restriction  base=”xsd:decimal”>

<xsd:fractionDigits value=”2”/> </xsd:restriction>

</xsd:simpleType>

</xsd:attribute>

</xsd:complexType>

<xsd:group name=”ShippingInfoGroup”> <xsd:all>

<xsd:element name=”DeliveryDate” type=”DateType”/> <xsd:element name=”Method” type=”DeliveryMethodType”/>

</xsd:all>

</xsd:group>

<xsd:group name=”BillingInfoGroup”> <xsd:all>

<xsd:element name=”BillingDate” type=”DateType”/> <xsd:element name=”PaymentMethod” type=”PaymentMethodType”/>

</xsd:all>

</xsd:group>

<xsd:complexType name=”InfoType”> <xsd:sequence>

<xsd:element name=”Name” minOccurs=”1” maxOccurs=”1”> <xsd:simpleType>

<xsd:restriction base=”xsd:string”/> </xsd:simpleType>

</xsd:element>

<xsd:element name=”Address” type=”AddressType” minOccurs=”1” ➥ maxOccurs=”1”/>

<xsd:choice minOccurs=”1” maxOccurs=”1”> <xsd:group ref=”BillingInfoGroup”/> <xsd:group ref=”ShippingInfoGroup”/>

</xsd:choice>

</xsd:sequence>

</xsd:complexType>

<xsd:simpleType name=”DateType”> <xsd:restriction base=”xsd:date”/>

</xsd:simpleType>

<xsd:simpleType name=”DeliveryMethodType”> <xsd:restriction base=”xsd:string”>

<xsd:enumeration value=”USPS”/> <xsd:enumeration value=”UPS”/> <xsd:enumeration value=”FedEx”/> <xsd:enumeration value=”DHL”/> <xsd:enumeration value=”Other”/>

</xsd:restriction>

</xsd:simpleType>

<xsd:complexType name=”OrderType”> <xsd:all>

<xsd:element name=”Product” type=”ProductType” ➥ minOccurs=”1” maxOccurs=”unbounded”/>

</xsd:all>

<xsd:attribute name=”SubTotal”> <xsd:simpleType>

<xsd:restriction base=”xsd:decimal”> <xsd:fractionDigits value=”2”/>

</xsd:restriction>

</xsd:simpleType>

</xsd:attribute>

<xsd:attribute name=”ItemsSold” type=”xsd:positiveInteger”/> </xsd:complexType>

<xsd:complexType name=”ProductType”> <xsd:attribute name=”Name” type=”xsd:string”/>

<xsd:attribute name=”Id” type=”xsd:positiveInteger”/> <xsd:attribute name=”Price”>

<xsd:simpleType>

<xsd:restriction base=”xsd:decimal”> <xsd:fractionDigits value=”2”/>

</xsd:restriction>

</xsd:simpleType>

</xsd:attribute>

<xsd:attribute name=”Quantity” type=”xsd:positiveInteger”/> </xsd:complexType>

</xsd:schema>

For a more detailed explanation regarding the schema in the preceding listing, refer to Chapter 4. As you can see from this listing, the XML Schema Definition Language can get rather complex and very detailed. But what about some of the other schema formats that have been proposed over time? We’ll take the rest of the chapter to discuss these alternative schema formats and compare them against the XML Schema from the preceding listing.