  In recent years, Software Transactional Memory systems (STMs) have garnered
significant interest as an elegant alternative for addressing concurrency
issues in memory. STM systems take optimistic approach. Multiple transactions
are allowed to execute concurrently. On completion, each transaction is
validated and if any inconsistency is observed it is aborted. Otherwise it is
allowed to commit.
  In databases a class of histories called as conflict-serializability (CSR)
based on the notion of conflicts have been identified, whose membership can be
efficiently verified. As a result, CSR is the commonly used correctness
criterion in databases. Similarly, using the notion of conflicts, a correctness
criterion, conflict-opacity (co-opacity) which is a sub-class of can be
designed whose membership can be verified in polynomial time. Using the
verification mechanism, an efficient STM implementation can be designed that is
permissive w.r.t co-opacity.
  By storing multiple versions for each transaction object, multi-version STMs
provide more concurrency than single-version STMs. But the main drawback of
co-opacity is that it does not admit histories that are uses multiple versions.
This has motivated us to develop a new conflict notions for multi-version STMs.
In this paper, we present a new conflict notion multi-version conflict. Using
this conflict notion, we identify a new subclass of opacity (a popular
correctness-criterion), mvc-opacity that admits multi-versioned histories and
whose membership can be verified in polynomial time. We show that co-opacity is
a proper subset of this class. The proposed conflict notion mv-conflict can be
applied on non-sequential histories as well unlike traditional conflicts.
Further, we believe that this conflict notion can be easily extended to other
correctness-criterion as well.
