XML documents which are used for exchanging structured documents between heterogeneous distributed system are increasing recently. It needs an object-oriented visualization tool for XML documents. So, we propose rules and an algorithm to represent structure of XML documents using UML Class Diagram. It helps to generate XML documents which are included links by understanding easily constructs of them and reduce gap of schema for them between heterogeneous databases. We propose formal models and modeling functions of XML links which provide an efficient environment for processing object-oriented documents.