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| Advances in distributed systems and networking technology have made interoperation not only feasible but also increasingly popular. We de ne the interoperation of secure systems and its security, and prove complexity and composability results on obtaining optimal and secure interoperation. Most problems are NP-complete even for systems with very simple access control structures, while for a general setting the problem is undecidable. Nevertheless, composability reduces complexity in that secure global interoperation can be obtained incrementally by composing secure local interoperation. We illustrate, through an application in secure database interoperation, how these theoretical results can help system designers in practice. Keywords| Computer security, database systems, interoperability, secure composability, algorithms, computational complexity.

This article measures education inequality between the coastal and inland provinces and compares it with rural-urban educational inequality in China, using Gini education coefficients and decomposition analysis. The main finding of the article is that disparities in access to education between rural and urban areas rather than between coastal and inland provinces are the major cause of educational inequality in China.