Вот контекст
In general, the present paper proposes a new formalism for describing the
main aspects of objects represented in the ODMG object model [4]. We struc-
ture objects into classes within a hierarchy with a formal definition of schema.
However, our definition of schema takes into account all static and all dynamic
aspects of objects as well as the concepts of inheritance, object identity and
overloading. Attributes and methods are treated semantically in a uniform way
as partial functions. This allows us to give a uniform rigorous formalization of
null values, undefinedness, and binding modes. This also allows us to define a
database schema in a way similar to an algebraic specification of data types
and to view a database instance as a state algebra of that specification. Basic
operations updating the state are formally defined by what we call an applicable
update set. Such a set consists of a set of parallel actions operating on a valid
state and providing a valid state. Each action creates or destroys an object or
updates an attribute. In a database context an applicable update set can be
regarded as a transaction.