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Static analysis of declarative languages deals with the detection, at compile time, of program properties that can be used to better understand the program semantics and to improve the efficiency of program evaluation. In logical update languages, an interesting problem is the detection of conflicting updates, inserting and deleting the same fact, for transactions based on set-oriented updates and active rules. In this paper, we investigate this topic in the context of the U-Datalog language, a set-oriented update language for deductive databases, based on a deferred semantics. We first formally define relevant properties of U-Datalog programs, mainly related to update conflicts. Then, we prove that the defined properties are decidable and we propose an algorithm to detect such conditions. Finally, we show how the proposed techniques can be applied to other logical update languages. Our results are based on the concept of labeling and query-tree.