Java: What is the Liquibase migration tool?

1<!-- changelog.xml -->
2<databaseChangeLog>
3  <changeSet id="1" author="dev">
4    <createTable tableName="users">
5      <column name="id" type="BIGINT" autoIncrement="true">
6        <constraints primaryKey="true"/>
7      </column>
8      <column name="name" type="VARCHAR(255)">
9        <constraints nullable="false"/>
10      </column>
11    </createTable>
12  </changeSet>
13  <changeSet id="2" author="dev">
14    <addColumn tableName="users">
15      <column name="email" type="VARCHAR(255)"/>
16    </addColumn>
17  </changeSet>
18</databaseChangeLog>