# 1-serializability theorem in database theory

In the paper "MVCC@TODS'1983 by Bernstein et al.", 1-serializability ($1$-$\text{SR}$) problem is defined as a decision problem:

To decide whether an MV (multi-version) log $L$ is $1$-$\text{SR}$.

where,

An MV (multi-version) log $L$ is $1$-$\text{SR}$ iff there exists a version order $\ll$ such that MVSG($L,\ll$) is acyclic.

I did not get the points of the following comment in page 475:

Our problem corresponds to choosing versions at the same time as scheduling the operations.

How to understand this comment? Has not the schedule been fixed once an MV log $L$ is given? Are the terms "choosing" and "scheduling" related to implementations?