José Ramón Garitagoitia

Fuzzy location and tracking on wireless networks

This paper describes user location and tracking on indoor scenarios through a wireless network. We propose a fuzzy location algorithm, using fuzzy inference systems, in order to deal with imprecise location based on radio-frequency trilateration estimations, providing high location rates near to 90. This indoor positioning approach is based on the pattern recognition of IEEE 802.11 (WiFi) signal strength measurements using fuzzy logic to deal with the vagueness and uncertainty of the trilateration based on signal strength. User location and tracking are considered in order to provide complete intelligent location based services. Fuzzy location techniques allow increasing location ratios even when the user trilateration can not be as precise as desired. Fuzzy tracking is performed by means of a fuzzy automaton.

Fuzzy automata with ε-moves compute fuzzy measures between strings

This paper introduces fuzzy automata with transitions by empty string (@?-moves), and shows their relationship with other classes of classical fuzzy automata. The @?-move represents a state change of the automaton without consuming any symbol of the input string. In approximate string matching, @?-moves allow to model the effect of the insertion of a symbol (one of the possible edit operations). We provide a fuzzy measure between strings based on the concepts of string alignments and fuzzy edit operations. The main contribution of this paper is to prove that a particular class of fuzzy automata with @?-moves computes those fuzzy measures without restricting the number of errors between the strings. Given a fuzzy measure, a building method for constructing the fuzzy automaton with @?-moves that computes it, is also proposed.

Fuzzy languages with infinite range accepted by fuzzy automata: Pumping Lemma and determinization procedure

Abstract The formulation of fuzzy automata allows us to select a great variety of triangular norms. Depending on the selected triangular norm, a fuzzy automaton can accept a fuzzy language (FA-language) with infinite range. These fuzzy automata are not equivalent to the so-called deterministic fuzzy automata (deterministic automata with a fuzzy subset of final states) which only accept fuzzy languages with finite range. In this paper, we study FA-languages with infinite range and a determinization procedure in order to obtain an equivalent fuzzy deterministic automaton for a given fuzzy automaton. A fuzzy deterministic automaton is a fuzzy automaton which satisfies the deterministic condition in its state transition function. The main contributions of our paper are: (1) a Pumping Lemma of FA-languages with infinite range; (2) the formulation of fuzzy deterministic automata and a Pumping Lemma of FDA-languages; (3) the necessary conditions for the determinization of fuzzy automata under continuous triangular norms which accept fuzzy languages of infinite range; and (4) a determinization algorithm for fuzzy automata, its correctness proof and performance.

Determinization of fuzzy automata via factorization of fuzzy states

Fuzzy finite-state automata over the algebra ([0,1],max,@?,0,1), in which the monoid ([0,1],@?,1) (@? denotes a continuous triangular norm) is not locally finite, can accept fuzzy languages of infinite range. For a given fuzzy finite-state automaton which accepts a fuzzy language of infinite range, we define the determinization of the fuzzy automaton via factorization of fuzzy states, i.e., the computation of an equivalent deterministic fuzzy automaton whether it is finite. This method of determinization is a generalization of the well-known accessible subset construction. Our main contribution is to determine that the representable-cycles property is the necessary and sufficient condition for determinization of a fuzzy finite-state automaton via a maximal factorization of fuzzy states. This property is more general than the twins property (adapted for fuzzy automata) which is the sufficient condition for weighted automata over the tropical semiring.

Mobility management in cellular communication systems using fuzzy systems

Mobility management in cellular communication systems is needed to guarantee quality of service, and to offer advanced services based on the user location. High mobility of terminals determines a high effort to predict next movement in order to grant a correct transition to the next phone cell. Then a fuzzy method dealing with the problem of determining the propagation path of a mobile terminal is introduced in this paper. Since multi-path fading and attenuation make difficult to determine the position of a terminal, the use of fuzzy symbols to model this situation allows to work better with this imprecise (fuzzy) information. Finally, the use of a fuzzy automaton allows to improve significatively the final recognition rate of the path followed by a mobile terminal.

A formal analysis of database replication protocols with SI replicas and crash failures

This paper provides a formal specification and proof of correctness of a basic Generalized Snapshot Isolation certification-based data replication protocol for database middleware architectures. It has been modeled using a state transition system, as well as the main system components, allowing a perfect match with the usual deployment in a middleware system. The proof encompasses both safety and liveness properties, as it is commonly done for a distributed algorithm. Furthermore, a crash failure model has been assumed for the correctness proof, although recovery analysis is not the aim of this paper. This allows an easy extension toward a crash-recovery model support in future works. The liveness proof focuses in the uniform commit: if a site has committed a transaction, the rest of sites will either commit it or it would have crashed.

Correctness proof of a database replication protocol under the perspective of the I/O automaton model

Correctness of recent database replication protocols has been justified in a rather informal way focusing only in safety properties and without using any rigorous formalism. Since a database replication protocol must ensure some degree of replica consistency and that transactions follow a given isolation level, previous proofs only focused in these two issues. This paper proposes a formalization using the I/O automaton model, identifying several components in the distributed system that are involved in the replication support (replication protocol, group communication system, database replicas) and specifying clearly their actions in the global replicated system architecture. Then, a general certification-based replication protocol guaranteeing the snapshot isolation level is proven correct. To this end, different safety and liveness properties are identified, checked and proved. Our work shows that some details of the replication protocols that were ignored in previous correctness justifications are indeed needed in order to guarantee our proposed correctness criteria.

A deterministic database replication protocol where multicastwritesets never get aborted

Several approaches for the full replication of data in distributed databases [1] have been studied. One of the preferred techniques is the eager update everywhere based on the total-order multicast delivery service [2], where the most outstanding varieties are: certification-based and weak-voting [1]. Under this approach, the execution flow of a transaction can be split into two different main phases: the first one, all operations are entirely executed at the delegate replica of the transaction; and followed by the second phase, started when the transaction requests its commit, all updates are collected and grouped (denoted as writeset) at the delegate replica and sent to all replicas. The commitment or abortion of a transaction is decided upon the delivery of the message. In the case of certification-based ones, each replica holds an ordered log of already committed transactions and the writeset is certified [3], against the log, to commit or abort the transaction. On the other hand, weak-voting ones atomically apply the delivered writeset at remote replicas whilst the delegate, if it is still active, reliably multicasts [2] a commit message. Thus, the certification-based presents a better behavior in terms of performance, only one message is multicast per transaction, but with higher abortion rates [1]. Recently, due to the use of DBMS providing SI, we have found several certification-based protocols to achieve, actually a weaker form called GSI [3], this isolation level in a replicated setting [3] while quite a few weak-voting ones [4].

A comment on Construction of fuzzy automata from fuzzy regular expressions

The aim of this comment is to point out that the fuzzy language recognized by a nondeterministic finite automaton, which is associated with a fuzzy regular expression, in the context of Stamenkovic-?irics method (Stamenkovic and ?iric (2012) 11]), is recognized by a fuzzy finite automaton with e-moves. Every fuzzy automaton with e-moves is also equivalent to a fuzzy automaton and there are effective methods for removing e-moves in order to obtain the equivalent fuzzy automaton. In this way, our proposal to convert a fuzzy regular expression to a fuzzy finite automaton is based on the construction of a fuzzy automaton with e-moves for the fuzzy regular expression and the construction of an equivalent fuzzy finite automaton by means of e-removal operation.

A formal characterization of SI-based ROWA replication protocols

Snapshot isolation (SI) is commonly used in some commercial DBMSs with a multiversion concurrency control mechanism since it never blocks read-only transactions. Recent database replication protocols have been designed using SI replicas where transactions are firstly executed in a delegate replica and their updates (if any) are propagated to the rest of the replicas at commit time; i.e. they follow the Read One Write All (ROWA) approach. This paper provides a formalization that shows the correctness of abstract protocols which cover these replication proposals. These abstract protocols differ in the properties demanded for achieving a global SI level and those needed for its generalized SI (GSI) variant - allowing reads from old snapshots. Additionally, we propose two more relaxed properties that also ensure a global GSI level. Thus, some applications can further optimize their performance in a replicated system while obtaining GSI.