Semistructured data is typically represented using XML. However, little semantic information can be captured using XML. Other data models, such as the Object Relationship Attribute data model for Semistructured data (ORASS), have been introduced to represent more detailed semantic information. Automatic analysis of the data models would enable us to reveal inconsistencies both at the schema and instance levels of the semistructured data. The aim of this paper is to encode the semantics of the ORA-SS data model in the Alloy formal language and automatically validate the semistructured data design using the Alloy Analyzer. It enables us to check the consistency of an ORA-SS schema and its instances.