On efficient top-

With the rapid development of blockchain, user’s daily financial bills and transfer records can be safely and completely stored in a transaction form. These transactions express commercial preferences for various scenarios and can be used to improve the quality of application services such as data analysis, data security, and recommendation systems. Therefore, there is a growing demand for processing diverse queries over blockchain transactions. In this paper, we formulate a new problem of blockchain top- k transaction path query (BCT k PQ) which returns first k transactions in a given query path according to the user-specified conditions. For processing BCT k PQ, we design a novel Collaborative Query Model (CQM) consisting of a set of collaborative peers and each of which contains three key components, i.e., parser, indexer and executor. First, in the parser, we propose a graph-based structure to denote the transaction paths. Then, in the indexer, we propose a two-level index to increase query and verification efficiency. Finally, in the executor, we present an optimized query algorithm for answering BCT k PQ securely and efficiently and further give a verification algorithm to guarantee the correctness of the query results. We conduct extensive experiments to illustrate the efficiency and effectiveness of our solution.