Schema for Object-Oriented XML (SOX)

Schema for Object-Oriented XML (SOX)

In 1997, Veo Systems Inc., submitted a note to the W3C concerning a new schema defin-ition language referred to as the Schema for Object-Oriented XML (SOX). SOX was developed primarily to assist in the development of large-scale, distributed electronic commerce applications. SOX provides a better alternative to DTDs for the creation of efficient software-development processes in distributed applications. SOX provides basic data types that can be extended, inheritance for attributes and content models, a powerful namespace mechanism, and documentation that can be embedded. Compared with DTDs, the Schema for Object-Oriented XML decreases the complexity of supporting interoperation among distributed applications by allowing various SOX processors to crunch the schema file to produce varying outputs in an automated fashion.

The SOX schema definition language is a grammar-based language very similar to that of the XML Schema Definition Language. Elements have “type” definitions and then are placed within parent elements through a declaration statement. In the case of the SOX schema definition language, the type definition comes in the form of the <elementtype> element. This element contains the basic type definition for an element. By using the <model> element within the <elementtype> element, a schema author can define the ele-ments’ definitions using element declarations, choices, attribute declarations, and so on. A sample SOX schema for Listing 6.1 is shown in Listing 6.6.

LISTING 6.6 PurchaseOrder.sox Contains a Sample SOX Schema for

PurchaseOrder.xml

<schema  name=”PurchaseOrder”>

<elementtype name=”PurchaseOrder”> <model>

<attdef name=”Tax” datatype=””/> <attdef name=”Total” datatype=””/>

<sequence>

<element name=”ShippingInformation”/> <element name=”BillingInformation”/> <element name=”Order”/>

</sequence>

</model>

</elementtype>

<elementtype name=”ShippingInformation”> <model>

<sequence>

<element name=”Name”/> <element name=”Address”/> <element name=”Method”/> <element name=”DeliveryDate”/>

</sequence>

</model>

</elementtype>

<elementtype name=”BillingInformation”> <model>

<sequence>

<element name=”Name”/> <element name=”Address”/> <element name=”PaymentMethod”/> <element name=”BillingDate”/>

</sequence>

</model>

</elementtype>

<elementtype name=”Name”> <model>

<string/>

</model>

</elementtype>

<elementtype name=”Method”> <model>

<string/>

</model>

</elementtype>

<elementtype name=”DeliveryDate”> <model>

<string datatype=”date”/> </model>

</elementtype>

<elementtype name=”PaymentMethod”> <model>

<string/>

</model>

</elementtype>

<elementtype name=”DeliveryDate”> <model>

<string datatype=”date”/> </model>

</elementtype>

<elementtype name=”Address”> <model>

<sequence>

<element name=”Street”/> <element name=”City”/> <element name=”State”/> <element name=”Zip”/>

</sequence>

</model>

</elementtype>

<elementtype name=”Street”> <model>

<string/>

</model>

</elementtype>

<elementtype name=”City”> <model>

<string/>

</model>

</elementtype>

<elementtype name=”State”> <model>

<string/>

</model>

</elementtype>

<elementtype name=”Zip”> <model>

<string/>

</model>

</elementtype>

<elementtype name=”Order”> <model>

<attdef name=”SubTotal” datatype=”number”/> <attdef name=”ItemsSold” datatype=”int”/> <sequence>

<element name=”Product” occurs=”+”/> </sequence>

</model>

</elementtype>

<elementtype name=”Product”> <model>

<empty/>

<attdef name=”Name” datatype=”string”/> <attdef name=”Id” datatype=”string”/> <attdef name=”Price” datatype = “number”/> <attdef name=”Quantity” datatype=”number”/>

</model>

</elementtype>

</schema>

From Listing 6.6, you can tell that the SOX schema definition language contains many similarities to the XML Schema Definition Language, XDR schemas, DCD schemas, and DSD schemas. The <elementtype> element contains the type definition for an element, which is then declared or referenced in other element type definitions.

The major difference between the W3C schema and the SOX schema is that in a SOX schema, if you redefine an element’s type definition, any other element that makes a ref-erence to the parent element type definition can also use the redefined or “subclassed” type definition in its place.