XML-based markup languages are widely used,e.g., for information exchange and as file formats in various software development and exploration tools.Still,using a metalanguage,such as XML,does not guarantee tool interoperability.The particular XML-based languages used by different tools often vary.They can,nonetheless, be processed by the same methods and tools.In most UML-based software development tools,support for tool interoperability is provided by using OMG ?s XML Metadata Interchange (XMI)as a file format.However, in many cases XMI has turned out to be insufficient for storing all information from the UML models.Thus the tool vendors typically extend and/or modify the language so introduce their own XMI dialect.This,in turn,means that the tool interoperability is sacrified. In this paper we discuss a method and a tool called DTD-compaper for exploring differences in exchange formats.DTD-compaper can,in general,be used to identify differences in grammars of XML-based languages.Further,we discuss three different case studies in which we used DTD-comparer.We first compare few commonly used XMI dialects.We further use the tool for comparing different versions of the Graph eXchange Language (GXL).