Referential actions as logical rules

Referential actions are specialized triggers used to automatically maintain referential integrity. While their local behavior can be grasped easily, it is far from clear what the combined e ect of a set of referential actions, i.e., their global semantics should be. For example, di erent execution orders may lead to ambiguities in determining the nal set of updates to be applied. To resolve these problems, we propose an abstract logical framework for rule-based maintenance of referential integrity: First, we identify desirable abstract properties like admissibility of updates which lead to a non-constructive global semantics of referential actions. We obtain a constructive de nition by formalizing a set of referential actions RA as logical rules, and show that the declarative semantics of the resulting logic program PRA captures the intended abstract semantics: The well-founded model of PRA yields a unique set of updates, which is a safe, sceptical approximation of the set of all maximal admissible updates � the third truth-value unde ned is assigned to all controversial updates. Finally, we show howtoobtaina characterization of all maximal admissible subsets of a given set of updates using certain maximal stable models.

A framework for navigation-driven lazy mediators

We propose a framework for navigation-driven evaluation of virtual mediated views. The approach is based on lazy mediators that translate incoming client navigations on a virtual XML view (or the result of an XML query) into navigations on wrapped sources or lower level mediators. Such a demand-driven approach is inevitable in order to handle up-to-date mediated views of huge Web sources or large query results, which are commonplace when querying the Web. The proposed MIX mediator provides to the client an abstraction of the DOM API, the de facto API to XML documents, hence hiding the non-materialization of the view or the query. We also describe the inherent navigational complexity of queries and view de nitions wrt. navigations. Next, we discuss the query/navigation processing aspects of the MIX mediator. The mediator translates a view into an algebraic plan. Then each operator of the algebraic plan acts as a navigation-driven lazy mediator. This allows to characterize the complexity of plans and to compare their navigational complexity.

Towards a Logical Semantics for Referential Actions in SQL

We investigate a logical semantics which unambiguously specifies the meaning of SQL-like referential actions of the form ON DELETE CASCADE and ON DELETE RESTRICT. The semantics is given by a translation of referential actions into logical rules. The proposed semantics is less restrictive than the standard SQL semantics, yet preserves all referential integrity constraints. First, a preliminary set of rules is introduced which rejects a set of user requests if a single request is rejected. Subsequently, a refined translation is presented using Statelog [LHL95], a state-oriented Datalog extension which allows to define active and deductive rules within a unified framework. We show that our semantics yields the maximal admissible subset of a given set of user requests. Apart from the Statelog formalization, a three-valued formalization based on the well-founded semantics and an equivalent gametheoretic specification are presented, which give further insight into the problem of ambiguity o..

Navigation-Driven Evaluation of Virtual Mediated Views

The MIX mediator systems incorporates a novel framework for navigation-driven evaluation of virtual mediated views. Its architecture allows the on-demand computation of views and query results as the user navigates them. The evaluation scheme minimizes superfluous source access through the use of lazy mediators that translate incoming client navigations on virtual XML views into navigations on lower level mediators or wrapped sources. The proposed demand-driven approach is inevitable for handling up-to-date mediated views of large Web sources or query results. The non-materialization of the query answer is transparent to the client application since clients can navigate the query answer using a subset of the standard DOM API for XML documents. We elaborate on query evaluation in such a framework and show how algebraic plans can be implemented as trees of lazy mediators. Finally, we present a new buffering technique that can mediate between the fine granularity of DOM navigations and the coarse granularity of real world sources

Observed vs. possible provenance

Provenance has been of interest to the Computer Science community for nearly two decades, with proposed uses ranging from data authentication, to security auditing, to ensuring trust in decision making processes. However, despite its enthusiastic uptake in the academic community, its adoption elsewhere is often hindered by the cost of implementation. In this paper we seek to alleviate some of these factors, and propose the idea of possible provenance in which we relax the constraint that provenance must be directly observed. We categorise some existing approaches to gathering provenance and compare the costs and benefits of each, and illustrate one method for generating possible provenance in more detail with a simple example: inferring the possible provenance of a game of Connect Four. We then go on to discuss some of the benefits and ramifications of this approach to gathering provenance, and suggest some key next steps in advancing this research