. The rule-based update language ULTRA has been designed for the specification of complex database updates in a modular fashion. The logical semantics of update goals is based on update request sets, which correspond to deferred basic updates in the database. The declarative character of the logical semantics leaves much freedom for various evaluation strategies, among them a top-down resolution, which can be naturally mapped onto a system of nested transactions. In this paper, we extend this operational model as follows: Not only the basic operations are performed and committed independently from the toplevel transaction, but also complex operations defined by update rules. This leads to an open nested transaction hierarchy, which allows to exploit the semantical properties of complex operations to gain more concurrency. On the other hand, high-level compensation is necessary and meta information must be provided by the programmer. We present the key elements of this combi...

In [WF97, WFF98a, WFF98b] we describe the language ULTRA that has been designed for the specification of database updates in a modular, rule-based fashion. We provide a model-theoretic semantics based on deferred updates, which means that update requests are determined and collected in an evaluation phase without changing the database state and the corresponding updates are performed in a subsequent materialization phase. As shown in [WFF98a, WFF98b], the semantics can be implemented using an optimistic transaction processing method. From a practical point of view, however, a straightforward implementation of the logical semantics is not satisfactory. In this paper we describe some of the arising problems and outline a flexible system architecture, which can serve as a framework for the implementation. Basic updates are performed (and even committed) on an underlying database system simultaneously with the logical evaluation of the ULTRA transactions. Recovery is done by issuing compen...

In this paper a logical framework called ULTRA is presented that can serve as the basis for a variety of update languages, among others extensions of the database language SQL, accommodating nested update queries and universal quantification over updates. We give a complete definition of the syntax and semantics of the ULTRA language based on concepts of logic databases. A natural candidate for an instantiation of the ULTRA framework is a database update language which we discuss in this paper as one example. However, the framework is not tied to database applications and can also deal with states and actions of other external systems such as robot control systems or workflow engines. The semantics of an update goal is defined as a structured transition. Depending on the selected execution model, the materialization of a transition can be either deferred or performed immediately.

In [20, 21, 22] we present the rule-based update language ULTRA. Updates are implemented by goals, and rules can be used to define complex operations to be reused in other goals. The concept is similar to procedures/functions in classical programming languages. Thus, it is possible to build arbitrarily complex database operations in a modular fashion. Constructs for concurrent composition, sequential composition, and bulk updates are provided, which subsume the classical database operations. The semantics of an update goal w.r.t. a fixed database state is defined in terms of update request sets which contain insertion and deletion requests for ground EDB tuples. This form of deferred updates, which describe transitions between databas...