The Extensible Markup Language (XML) is becoming a de-facto standard for exchanging information among the web applications. Efficient implementation of web application needs to be efficient implementation of XML and XML schema document. The quality of XML document has great impact on the design quality of its schema document. Therefore, the design of XML schema document plays an important role in web engineering process and needs to have many schema qualities: functionality, extensibility, reusability, understandability, maintainability and so on. Three schema metrics: Reusable Quality metric (RQ), Extensible Quality metric (EQ) and Understandable Quality metric (UQ) are proposed to measure the Reusable, Extensible and Understandable of XML schema documents in web engineering process respectively. The base attributes are selected according to XML Quality Assurance Design Guidelines. These metrics are formulated based on Binary Entropy Function and Rank Order Centroid method. To check the validity of the proposed metrics empirically and analytically, the self-organizing feature map (SOM) and Weyuker’s 9 properties are used.