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It is increasingly common to find complex data represented through the graph model. Contrary to relational models, graphs offer a high capacity for executing analytical tasks on complex data. Since a huge amount of data is still presented in terms of relational tables, it is necessary to understand how to translate this data into graphs. This paper proposes a complete mapping process that allows transforming any relational database (schema and instance) into a property graph database (schema and instance). Contrary to existing mappings, our solution preserves the three fundamental mapping properties, namely: information preservation, semantic preservation and query preservation. Moreover, we study mapping any SQL query into an equivalent Cypher query, which makes our solution practical. Existing solutions are either incomplete or based on non-practical query language. Thus, this work is the first complete and practical solution for mapping relations to graphs.

We consider the class of conditional graph patterns (\emph{CGPs}) that allow user to query data graphs with complex patterns that contain negation and predicates. To overcome the prohibitive cost of subgraph isomorphism, we consider matching of \emph{CGPs} under simulation semantics which can be conducted in quadratic time. In emerging applications, one would like to reduce more this matching time, and the static analysis of patterns may allow ensuring part of this reduction. We study the containment problem of \emph{CGPs} that aims to check whether the matches of some pattern $P_1$, over any data graph, are contained in those of another pattern $P_2$ (written $P_1\sqsubseteq P_2$). The optimization process consists to extract matches of $P_1$ only from those of $P_2$ without querying the (possibly large) data graph. We show that the traditional semantics of containment is decidable in quadratic time, but it fails to meet the optimization goal in the presence of negation and predicates. To overcome this limit, we propose a new semantics of containment, called \emph{strong containment}, that is more suitable for \emph{CGPs} and allows to reduce their matching time. We show that \emph{strong containment} can be decided in cubic time by providing such an algorithm. We are planing to use results of this paper to answer \emph{CGPs} using views. This paper is part of an ongoing project that aims to design a caching system for complex graph patterns.

Graph pattern matching is a routine process for a wide variety of applications such as social network analysis. It is typically defined in terms of subgraph isomorphism which is NP-Complete. To lower its complexity, many extensions of graph simulation have been proposed which focus on some topological constraints of pattern graphs that can be preserved in polynomial-time over data graphs. We discuss in this paper the satisfaction of a new topological constraint, called Label-Repetition constraint. To the best of our knowledge, existing polynomial approaches fail to preserve this constraint, and moreover, one can adopt only subgraph isomorphism for this end which is cost-prohibitive. We present first a necessary and sufficient condition that a data subgraph must satisfy to preserve the Label-Repetition constraints of the pattern graph. Furthermore, we define matching based on a notion of triple simulation, an extension of graph simulation by considering the new topological constraint. We show that with this extension, graph pattern matching can be performed in polynomial-time, by providing such an algorithm. Our algorithm is sub-quadratic in the size of data graphs only, and quartic in general. We show that our results can be combined with orthogonal approaches for more expressive graph pattern matching., Comment: 19 pages, 4 figures

Over the past years several works have proposed access control models for XML data where only read-access rights over non-recursive DTDs are considered. A few amount of works have studied the access rights for updates. In this paper, we present a general model for specifying access control on XML data in the presence of update operations of W3C XQuery Update Facility. Our approach for enforcing such updates specifications is based on the notion of query rewriting where each update operation defined over arbitrary DTD (recursive or not) is rewritten to a safe one in order to be evaluated only over XML data which can be updated by the user. We investigate in the second part of this report the secure of XML updating in the presence of read-access rights specified by a security views. For an XML document, a security view represents for each class of users all and only the parts of the document these users are able to see. We show that an update operation defined over a security view can cause disclosure of sensitive data hidden by this view if it is not thoroughly rewritten with respect to both read and update access rights. Finally, we propose a security view based approach for securely updating XML in order to preserve the confidentiality and integrity of XML data., Comment: No. RR-7870 (2012)

Most state-of-the art approaches for securing XML documents allow users to access data only through authorized views defined by annotating an XML grammar (e.g. DTD) with a collection of XPath expressions. To prevent improper disclosure of confidential information, user queries posed on these views need to be rewritten into equivalent queries on the underlying documents. This rewriting enables us to avoid the overhead of view materialization and maintenance. A major concern here is that query rewriting for recursive XML views is still an open problem. To overcome this problem, some works have been proposed to translate XPath queries into non-standard ones, called Regular XPath queries. However, query rewriting under Regular XPath can be of exponential size as it relies on automaton model. Most importantly, Regular XPath remains a theoretical achievement. Indeed, it is not commonly used in practice as translation and evaluation tools are not available. In this paper, we show that query rewriting is always possible for recursive XML views using only the expressive power of the standard XPath. We investigate the extension of the downward class of XPath, composed only by child and descendant axes, with some axes and operators and we propose a general approach to rewrite queries under recursive XML views. Unlike Regular XPath-based works, we provide a rewriting algorithm which processes the query only over the annotated DTD grammar and which can run in linear time in the size of the query. An experimental evaluation demonstrates that our algorithm is efficient and scales well., Comment: (2011)