2.3　Truly Concurrent Process Algebra-APTC

APTC eliminates the differences of structures of transition systems，event structures，etc.，and discusses their behavioral equivalences.It considers two kinds of causality relations：the chronological order modeled by sequential composition and the causal order between different parallel branches modeled by communication merge.It also considers two kinds of confliction relations：the structural confliction modeled by alternative composition and the conflicts in different parallel branches that should be eliminated.Based on conservative extension，APTC has four modules：BATC（Basic Algebra for True Concurrency），APTC（Algebra for Parallelism in True Concurrency），recursion and abstraction.