A Purpose-Based Synchronization Protocol of Multiple Transactions

In a peer-to-peer (P2P) system, multiple peer processes issue transactions to manipulate objects. A transaction issued by a process is assigned with a subfamily of roles named purpose, which are granted to the process. If a transaction reads an object o₁ and then writes another object o₂, information in o₁ might flow into o₂. Suppose a transaction T₁ with a purpose R₁ precedes another transaction T₂ with a purpose R₂ in a schedule. Here, if the legal information flow relation R₁ ¿ R₂ holds, no illegal information flow occur. Otherwise, illegal information flow might occur. In order to prevent illegal information flow, if T₁ writes an object o, the object o is marked with the purpose R₁. The transaction T₂ is allowed to read the object o if R₁ ¿ R₂. Even if T₁ commits, the object o isstill marked with the purpose R₁. Hence, every transaction T₃ with such a purpose R₃ that R₁ does not legally flow into R₃ is aborted if T₃ reads the object o. In result, the throughput is degraded. In this paper, we discuss how to release purpose marks on objects. Objects whose information may flow into an object o are source objects of o. If the source objects are changed, a purpose mark on the object o is released. In addition, an object o might have some lifetime when o´s data has to be secure since the data iscreated. If it takes time since the object o is marked, the purpose mark is released. While there occur no illegal information flow in our purpose marking (PM) protocol, transactions which imply illegal information flow are aborted. We evaluate the PM protocol in terms of how many transactions are aborted.