The Internet's core routing infrastructure, while arguably robust and e#cient, has proven to be di#cult to evolve to accommodate the needs of new applications. Prior research on this problem has included new hard-coded routing protocols on the one hand, and fully extensible Active Networks on the other. In this paper, we explore a new point in this design space that aims to strike a better balance between the extensibility and robustness of a routing infrastructure. The basic idea of our solution, which we call declarative routing, is to express routing protocols using a database query language. We show that our query language is a natural fit for routing, and can express a variety of well-known routing protocols in a compact and clean fashion. We discuss the security of our proposal in terms of its computational expressive power and language design. Via simulation, and deployment on PlanetLab, we demonstrate that our system imposes no fundamental limits relative to traditional protocols, is amenable to query optimizations, and can sustain long-lived routes under network churn and congestion.

The networking and distributed systems communities have recently explored a variety of new network architectures, both for applicationlevel overlay networks, and as prototypes for a next-generation Internet architecture. In this context, we have investigated declarative networking: the use of a distributed recursive query engine as a powerful vehicle for accelerating innovation in network architectures [23, 24, 33]. Declarative networking represents a significant new application area for database research on recursive query processing. In this paper, we address fundamental database issues in this domain. First, we motivate and formally define the Network Datalog (NDlog) language for declarative network specifications. Second, we introduce and prove correct relaxed versions of the traditional semi-na ve query evaluation technique, to overcome fundamental problems of the traditional technique in an asynchronous distributed setting. Third, we consider the dynamics of network state, and formalize the "eventual consistency" of our programs even when bursts of updates can arrive in the midst of query execution. Fourth, we present a number of query optimization opportunities that arise in the declarative networking context, including applications of traditional techniques as well as new optimizations. Last, we present evaluation results of the above ideas implemented in our P2 declarative networking system, running on 100 machines over the Emulab network testbed.

Query containment and query answering are two important computational tasks in databases. While query answering amounts to compute the result of a query over a database, query containment is the problem of checking whether for every database, the result of one query is a subset of the result of another query. In this paper, we deal with unions of conjunctive queries, and we address query containment and query answering under Description Logic constraints. Every such constraint is essentially an inclusion dependency between concepts and relations, and their expressive power is due to the possibility of using complex expressions in the specification of the dependencies, e.g., intersection and difference of relations, special forms of quantification, regular expressions over binary relations. These types of constraints capture a great variety of data models, including the relational, the entity-relationship, and the object-oriented model, all extended with various forms of constraints. They also capture the basic features of the ontology languages used in the context of the Semantic Web. We present the following results on both query containment and query answering. We provide a method for query containment under Description Logic constraints, thus showing that the problem

The problem of deciding query containment has important applications in classical query optimization and heterogeneous database systems. Query containment is undecidable for unrestricted recursive queries, and decidable for recursive monadic queries and conjunctive queries over regular path expressions. In this paper, we identify a new class of recursive queries with decidable containment. Our framework extends the aforementioned query classes by supporting recursive predicates with more than two arguments and nonlinear recursion. 1.

The paper investigates fundamental decision problems and composition synthesis for Web services commonly found in practice. We propose a notion of synthesized Web services (SWS’s) to specify the behaviors of the services. Upon receiving a sequence of input messages, an SWS issues multiple queries to a database and generates actions, in parallel; it produces external messages and database updates by synthesizing the actions parallelly generated. In contrast to previous models for Web services, SWS’s advocate parallel processing and (deterministic) synthesis of actions. We classify SWS’s based on what queries an SWS can issue, how the synthesis of actions is expressed, and whether unbounded input sequences are allowed in a single interaction session. We show that the behaviors of Web services supported by various prior models, data-driven or not, can be specified by different SWS classes. For each of these classes we study the non-emptiness, validation and equivalence problems, and establish matching upper and lower bounds on these problems. We also provide complexity bounds on composition synthesis for these SWS classes, identifying decidable cases.

Decentralized data management has been addressed during the years by means of several technical solutions, ranging from distributed DBMSs, to mediatorbased data integration systems. Recently, such an issue has been investigated in the context of Peer-to-Peer (P2P) architectures. In this chapter we focus on P2P data integration systems, which are characterized by various autonomous peers, each peer being essentially an autonomous information system that holds data and is linked to other peers by means of P2P mappings. P2P data integration does not rely on the notion of global schema, as in traditional mediator-based data integration. Rather, it computes answers to users ’ queries, posed to any peer of the system, on the basis of both local data and the P2P mappings, thus overcoming the main drawbacks of centralized mediator-based data integration systems and providing the foundations of effective data management in virtual organizations. In this chapter we first survey the most significant approaches proposed in the literature for both mediator-based data integration and P2P data management. Then, we focus on advanced schema-based P2P systems for which the aim is semantic integration of data, and analyze the commonly adopted approach of interpreting such systems using a first-order semantics. We show some weaknesses of this approach, and compare it with an alternative approach, based on multi-modal epistemic semantics, which reflects the idea that each peer is conceived as a rational agent that exchanges knowledge/belief with other peers. We consider several central properties of P2P data integration systems: modularity, generality, and decidability. We argue that the approach based on epistemic logic is superior with respect to all the above properties.

Abstract. In concurrent database systems, correctness of update transactions refers to the equivalent effects of the execution schedule and some serial schedule over the same set of transactions. Integrity constraints add further semantic requirements to the correctness of the database states reached upon the execution of update transactions. Several methods for efficient integrity checking and enforcing exist. We show in this paper how to apply one such method to automatically extend update transactions with locks and simplified consistency tests on the locked entities. All schedules produced in this way are conflict serializable and preserve consistency. For certain classes of databases we also guarantee that the amount of locked database entities is minimal. 1

nutt<at>inf.unibz.it Abstract. We study containment of conjunctive queries that are evaluated over databases that may contain tuples with null values. We assume the semantics of SQL for single block queries with a SELECT DISTINCT clause. This problem (“null containment ” for short) is different from containment over databases without null values and sometimes more difficult. We show that null-containment for boolean conjunctive queries is NPcomplete while it is Π P 2-complete for queries with distinguished variables. However, if no relation symbol is allowed to appear more than twice, then null-containment is polynomial, as it is for databases without nulls. If we add a unary test predicate IS NULL, as it is available in SQL, then containment becomes Π P 2-hard for boolean queries, while it remains in Π P 2 for arbitrary queries. 1

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