With the advance of E-Commerce over Web-based information, the interoperability of isolated XML repositories and databases over the Internet has drawn an increasing interest recently. Little effort, however, has been made to preserve necessary autonomy and security of each individual XML repository or database during information exchange or evolution. Generic model management has been intensively researched and also implemented in a prototype since its first introduction. Security related research is yet to be conducted for model management. This paper presents a uniform security model for access control specifications of heterogeneous data models over the Web. Based on the uniform representation, we present security extensions to our previous work on visual model management operators for managing access control specifications to allow heterogeneous Web data models to exchange information over public networks.