Mathematics is forcing towards a consistent framework of theory development. Computer Science is an engineering discipline and sometimes suffers from ad-hoc definitions. Transactions are a concept that is commonly used in the database area. It is often defined in the form: given a syntactic construct in act form and declare a number of properties an engine should support which is not specified and invisible. This paper aims in providing an operational semantics for transactions. A DBMS implementation is then considered to be a faithful refinement of the operational semantics.