XML is the common data format in the exchanges between Business and Operations Support Systems (B/OSS). The exchanges carry business objects (BO) which are identified by one of more member elements. This article is about how to declare and use object keys in XMLs in the context of an Enterprise Information System (EIS).
The key or identity information of a XML business object (XML-BO) is a "metadata" aspect: it is not explicit in the XML, instead is defined separately, as meta-data, known by the components that process the data. XML meta-data can be described in multiple ways. The one that I will use in this article, and the most common, is the XML Schema Definition (XSD).
XSD does not directly support the concept of object ID but has related constructs. One of them is the ability to declare element identity constraints using the XSD elements: ID/IDREF/IDREFS and KEY/KEYREF. These constructs are used to impose uniqueness and/or referential integrity within an instance of XML. They are not intended as having a cross-instances meaning. But maybe, extending the semantic, we can use these constructs to define object identity in an EIS context.