Autor: Orejas, Fernando
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orejas@lsi.upc.edu
orejas@cs.upc.edu
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Universitat Politècnica de Catalunya, Spain
UPC, Spain
UPC, Spain
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Artículo A Logic of Graph Conditions Extended with PathsNavarro, Marisa; Orejas, Fernando; Pino, Elvira; Lambers, Leen. Actas de las XVI Jornadas de Programación y Lenguajes (PROLE 2016), 2016-09-02.In this paper we tackle the problem of extending the logic of nested graph conditions with paths. This means, for instance, that we may state properties about the existence of paths between some given nodes. As a main contribution, a sound and complete tableau method is defined for reasoning about this kind of properties.Artículo Problemas de confluencia en transformación de grafos: de los pares críticos a los conflictos iniciales.Orejas, Fernando. Actas de las XXII Jornadas sobre Programación y Lenguajes (PROLE 2023), 2023-09-12.Mucha gente cree que la transformación de grafos no es nada más que una generalización de la reescritura de términos. Sin embargo, en este tutorial vetemos que la técnica que se usa en reescritura de términos para la comprobación de la confluencia, el cálculo de los pares críticos y la comprobación de su convergencia, genera problemas serios cuando se adapta a la transformación de grafos. Adicionalmente, veremos cómo se resuelven, en mayor o menor medida, estos problemas a traves del nuevo concepto de conflicto inicial.Artículo Towards a Logical Approach to Graph DatabasesPino, Elvira; Orejas, Fernando; Mylonakis, Nicos; Pasarella, Edelmira. Actas de las XXI Jornadas de Programación y Lenguajes (PROLE 2022), 2022-09-05.Graph databases are now playing an important role, not only because they allow us to overcome some limitations of relational databases, but also because they provide a good model for searching the web. In particular, graph databases differ from relational databases in that the topology of data is as important as the data itself. Thus, typical graph database queries are navigational, asking whether some nodes are connected by paths satisfying some specific properties. While relational databases were designed upon logical and algebraic foundations, the development of graph databases has been quite ad-hoc. In this sense, the aim of this paper is to provide them with some logical foundations. More precisely, in previous work we introduced a navigational logic, called +AFw-GNL+AFw (Graph Navigational Logic) that allows us to describe graph navigational properties. Moreover, this logic is equipped with a deductive tableau method that we proved to be sound and complete. In the current paper, we show how graph queries +AHsAXA-it +AOA la+AH0 Cypher can be expressed using a fragment of +AFw-GNL, defining for them a logical and an operational semantics. Moreover, we show that this operational semantics is sound and complete.Artículo Incremental Concurrent Synchronization with Conflict ResolutionPino, Elvira; Navarro, Marisa; Orejas, Fernando. Actas de las XIX Jornadas de Programación y Lenguajes (PROLE 2019), 2019-09-02.In the context of software model-driven development, artifacts are specified by several models describing different aspects, e.g., different views, dynamic behaviour, structure, etc. Then, a given set of models is emph{consistently integrated} if they describe some artifact. Along the process of designing and implementing an artifact, and also after the artifact is implemented, it may be common to modify or update some aspects of a given model, or of several models. These changes may cause an inconsistency between the given set of models. To restore consistency, we have to emph{propagate} the given modifications to the rest of the models. This process is called emph{model synchronization}. If each time we propagate the updates on just one model, synchronization is emph{sequential}, but if we propagate simultaneously updates on two models, synchronization is called emph{concurrent}. The sequential case is quite simpler than the concurrent one, since in the latter case we may have to deal with conflicts between the modifications applied to different models, implying that we may need to backtrack some updates. For simplicity, we assume that the set of models describing an artifact consists just of two models. Then, following the ideas of a previous paper on sequential synchronization, in the current paper, we propose an incremental procedure for the concurrent case, meaning that our procedure does not build the resulting models from scratch, but it only modifies the parts of the models affected by the update.Artículo The Semantics of GQL-like Path QueriesOrejas, Fernando; Pino, Elvira. Actas de las XXIII Jornadas de Programación y Lenguajes (PROLE 2024), 2024-06-17.The success of graph databases (GDBs) has caused the development of several dozens of GDB products by companies like Neo4j, Oracle, Amazon, IBM or SAP. In parallel, several graph query languages have been designed for querying these GDBs, like Cypherfor Neo4j, PGQL for Oracle, or GSQL for TigerGraph, which actually are quite similar. This situation has led to propose the creation of a unifying standard for graph query languages. This standard is currently under development, and is called GQL. However, GQL has gone beyond the expressive power of the above mentioned languages in several senses. In a previous paper we defined a logical and an operational semantics for a core language similar to Cypher, showing that the operational semantics is sound and complete with respect to the logical one. Now, in the current work, our aim is to redefine the semantics that we gave for Cypher-like languages to a core subset of GQL.