XPath Queries Research Articles

A gossip-based approach for Internet-scale cardinality estimation of XPath queries over distributed semistructured data

In this paper, we address the problem of cardinality estimation of XPath queries over XML data stored in a distributed, Internet-scale environment such as a large-scale, data sharing system designed to foster innovations in biomedical and health informatics. The cardinality estimate of XPath expressions is useful in XQuery optimization, designing IR-style relevance ranking schemes, and statistical hypothesis testing. We present a novel gossip algorithm called XGossip, which given an XPath query estimates the number of XML documents in the network that contain a match for the query. XGossip is designed to be scalable, decentralized, and robust to failures--properties that are desirable in a large-scale distributed system. XGossip employs a novel divide-and-conquer strategy for load balancing and reducing the bandwidth consumption. We conduct theoretical analysis of XGossip in terms of accuracy of cardinality estimation, message complexity, and bandwidth consumption. We present a comprehensive performance evaluation of XGossip on Amazon EC2 using a heterogeneous collection of XML documents.

An Effective XML Storage Method Based on Deleting XPath Query Minimization

The storage method for XML data in database will affect the efficiency of XML keywords querying, indexing and updating significantly. In most cases, the XPath sentences provided by user are not refined. These queries can often achieve minimization by deleting redundant parts. It means the minimized query is one of subsets of this query. Such kind of minimization query is method based on deleting queries. The steps are determining nodes relations, finding redundant nodes, deleting redundant nodes and sub-tree and obtain final minimization query tree. In this paper, we propose an improved XPath query minimization method based on deletion using simulation concept. Experiments analysis results show that with introduction of appropriate indexing and new algorithm, the XML keywords indexing efficiency can be significantly improved.

Relational Storage for XML Rules

Very few research works have been done on XML security over relational databases despite that XML became the de facto standard for the data representation and exchange on the internet and a lot of XML documents are stored in RDBMS. In [14], the author proposed an access control model for schema-based storage of XML documents in relational storage and translating XML access control rules to relational access control rules. However, the proposed algorithms had performance drawbacks. In this paper, we will use the same access control model of [14] and try to overcome the drawbacks of [14] by proposing an efficient technique to store the XML access control rules in a relational storage of XML DTD. The mapping of the XML DTD to relational schema is proposed in [7]. We also propose an algorithm to translate XPath queries to SQL queries based on the mapping algorithm in [7].

Partial Evaluation for Distributed XPath Query Processing and Beyond

This article proposes algorithms for evaluating XPath queries over an XML tree that is partitioned horizontally and vertically, and is distributed across a number of sites. The key idea is based on partial evaluation: it is to send the whole query to each site that partially evaluates the query, in parallel, and sends the results as compact (Boolean) functions to a coordinator that combines these to obtain the result. This approach possesses the following performance guarantees. First, each site is visited at most twice for data-selecting XPath queries, and only once for Boolean XPath queries. Second, the network traffic is determined by the answer to the query, rather than the size of the tree. Third, the total computation is comparable to that of centralized algorithms on the tree stored in a single site, regardless of how the tree is fragmented and distributed. We also present a MapReduce algorithm for evaluating Boolean XPath queries, based on partial evaluation. In addition, we provide algorithms to evaluate XPath queries on very large XML trees, in a centralized setting. We show both analytically and empirically that our techniques are scalable with large trees and complex XPath queries. These results, we believe, illustrate the usefulness and potential of partial evaluation in distributed systems as well as centralized XML stores for evaluating XPath queries and beyond.

XML-Based RDF Data Management for XPath Query Language

The Semantic Web is an extention of the current Web that will allow to find, share and combine information more easily. The meaning in the Semantic Web is mostly represented by Resource Description Framework (RDF). To harvest such power requires robust and scalable data repositories that can store RDF data. Most of the existing RDF storage techniques rely on relation model and relational database technologies for these tasks. The mis-match between the graph model of the RDF data and the rigid 2D tables of relational model jeopardizes the scalability of such repositories and frequently renders a repository inefficient for some types of data and queries. This paper proposed a system that can store RDF data in the XML repository and discuss the basic idea of conversion from RDF Schema to XML Schema and XPath queries for extract information from XML database. DOI: http://dx.doi.org/10.11591/ij-ict.v2i1.1503

Answering queries using views over probabilistic XML

We study the complexity of query answering using views in a probabilistic XML setting, identifying large classes of XPath queries -- with child and descendant navigation and predicates -- for which there are efficient (PTime) algorithms. We consider this problem under the two possible semantics for XML query results: with persistent node identifiers and in their absence. Accordingly, we consider rewritings that can exploit a single view, by means of compensation, and rewritings that can use multiple views, by means of intersection. Since in a probabilistic setting queries return answers with probabilities, the problem of rewriting goes beyond the classic one of retrieving XML answers from views. For both semantics of XML queries, we show that, even when XML answers can be retrieved from views, their probabilities may not be computable. For rewritings that use only compensation, we describe a PTime decision procedure, based on easily verifiable criteria that distinguish between the feasible cases -- when probabilistic XML results are computable -- and the unfeasible ones. For rewritings that can use multiple views, with compensation and intersection, we identify the most permissive conditions that make probabilistic rewriting feasible, and we describe an algorithm that is sound in general, and becomes complete under fairly permissive restrictions, running in PTime modulo worst-case exponential time equivalence tests. This is the best we can hope for since intersection makes query equivalence intractable already over deterministic data. Our algorithm runs in PTime whenever deterministic rewritings can be found in PTime.

ANDES: efficient evaluation of NOT-twig queries in relational databases

Despite a large body of work on XPath query processing in relational environment, systematic study of queries containing not-predicates have received little attention in the literature. Particularly, several xml supports of industrial-strength commercial rdbms fail to efficiently evaluate such queries. In this paper, we present an efficient and novel strategy to evaluate not -twig queries in a tree-unaware relational environment. not -twig queries are XPath queries with ancestor---descendant and parent---child axis and contain one or more not-predicates. We propose a novel Dewey-based encoding scheme called Andes (ANcestor Dewey-based Encoding Scheme), which enables us to efficiently filter out elements satisfying a not-predicate by comparing their ancestor group identifiers. In this approach, a set of elements under the same common ancestor at a specific level in the xml tree is assigned same ancestor group identifier. Based on this scheme, we propose a novel sql translation algorithm for not-twig query evaluation. Experiments carried out confirm that our proposed approach built on top of an off-the-shelf commercial rdbms significantly outperforms state-of-the-art relational and native approaches. We also explore the query plans selected by a commercial relational optimizer to evaluate our translated queries in different input cardinality. Such exploration further validates the performance benefits of Andes.

Fuzzy Logic Programming for Implementing a Flexible XPath-based Query Language

FLOPER is the “Fuzzy LOgic Programming Environment for Research” designed in our research group for assisting the development of real-world applications where fuzzy logic might play an important role. This is the case of our recently proposed extension for the popular XPath query language in order to handle flexible queries which provide ranked answers, fuzzy variants of operators and, or and avg for XPath conditions, as well as two structural constraints, called down and deep, for which a certain degree of relevance can be associated.

Parallel Tree Reduction on MapReduce

MapReduce, the de facto standard for large scale data-intensive applications, is a remarkable parallel programming model, allowing for easy parallelization of data intensive computations over many machines in a cloud. As huge tree data such as XML has achieved the status of the de facto standard for representing structured information, the situation calls for effcient MapReduce programs treating such a tree data structure in parallel. However, development of such MapReduce programs has remained a challenge. In this paper, restructuring our previous BSP algorithm for tree reduction computations, we propose a new MapReduce algorithm that can be used to implement various tree computations such as XPath queries. Our algorithm is designed to achieve linear speedup even for extreme inputs, and our experimental result shows that our prototype implementation actually achieves linear speedup even for monadic trees.

How XPath Query Minimization Impacts Query Processing Performance

How XPath Query Minimization Impacts Query Processing Performance

Fiber processing of queries on hierarchical data

This paper is dealing with fiber processing of XPath queries. We make use of the Structural Join (SJ) method that we modify so as to achieve an improved number of page fetches containing input data. The fiber aggregation based composition, defined in this paper, allows local optimization of individual search steps taking advantage either of input low cardinality or high selectiveness of parent-child join.

Faster bit-parallel algorithms for unordered pseudo-tree matching and tree homeomorphism

In this paper, we consider the unordered pseudo-tree matching problem, which is a problem of, given two unordered labeled trees P and T, finding all occurrences of P in T via such many-to-one matchings that preserve node labels and parent–child relationship. This problem is closely related to the tree pattern matching problem for XPath queries with child axis only. If m>w, we present an efficient algorithm that solves the problem in O(nmlog(w)/w) time using O(hm/w+mlog(w)/w) space and O(mlog(w)) preprocessing on a unit-cost arithmetic RAM model with addition, where m is the number of nodes in P, n is the number of nodes in T, h is the height of T, and w is the word length, and we assume that w⩾logn. We also discuss a modification of our algorithm for the unordered tree homeomorphism problem, which corresponds to the tree pattern matching problem for XPath queries with descendant axis only.

XPath Query Relaxation through Rewriting Rules

Query relaxation is the process of weakening a query to a more general one, and it is frequently employed to support approximate query answering. In this paper, rewriting systems for a wide fragment of XPath are investigated, which accomplish query relaxation through the application of simple rewriting rules transforming navigational axes and node tests into relaxed ones. Specifically, a general yet simple form of rewriting rules is considered, which subsumes the forms adopted in several rewriting systems for approximate XPath query answering. The expressiveness of rewriting systems based on this form of rules is characterized in terms of their capability of transforming a query into every more general formulation. It is shown that traditional rewriting systems are not only incomplete w.r.t. containment, but also w.r.t. the stricter form known as containment by homomorphism. This limitation is overcome by defining a set R* of rewriting rules which are still of the same simple form of traditional ones, but are expressive enough to catch at least containment by homomorphism. Then, an algorithm is proposed which exploits R* to provide approximate answers of queries along with a measure of their approximation degree.

PXpathV: Preventing XPath Injection Vulnerabilities in Web Applications

Generally, most Web applications use relational databases to store and retrieve information. But, the growing acceptance of XML technologies for documents it is logical that security should be integrated with XML solutions. In a web application,an improper user inputs is a main cause for a wide variety of attacks. XML Path or XPath language is used for querying information from the nodes of an XML document. XPath Injection is an attack technique, much like SQL injection, exists when a malicious u ser can insert arbitrary XPath code into form fields and URL query parameters in order to inject this code directly into the XPath query evaluation engine. Through the crafted input a malicious user would bypass authentication or to access restricted data from the XML data source.Hence, we proposed an approach to detect XPath injection attack in XML databases at runtime. Our approach intercept XPath expression and parse the XQuery expression to find the inputs to be placed in the expression. The identified inputs are used to design an XML file and it would be validated through a schema.

Models XP for Rewriting XPath Queries

Models XP for Rewriting XPath Queries

Efficient Processing of XML Path Queries Using BI Index

XML has been widely used for information exchange and storage as the de facto data representation format nowadays. Several XML query languages such XPath, XQuery and XML-QL have been proposed. Many structural join algorithms have been proposed for processing XPath queries, Although holistic twig join algorithms has been proved to be I/O optimal in terms of input and output sizes for queries with only ancestor-descendant edges, it cannot control the size of intermediate results for queries with parent-child edges. We address the problem of efficient path queries with mixed of ancestor-descendant and parent-child edges on a simple but novel index, called BI (i.e. Binary Index) based on Dewey labeling scheme. And we propose a new holistic path join algorithm, namely PSBI, which has the same performance as PathStack for query path with only ancestor-descendant edges, but it is significantly more efficient than PathStack for queries with the presence of parent-child edges. Experimental results demonstrate that the PSBI and BI index has a substantial performance improvement compared to original PathStack algorithm.

Alternating automata on data trees and XPath satisfiability

A data tree is an unranked ordered tree whose every node is labeled by a letter from a finite alphabet and an element (“datum”) from an infinite set, where the latter can only be compared for equality. The article considers alternating automata on data trees that can move downward and rightward, and have one register for storing data. The main results are that nonemptiness over finite data trees is decidable but not primitive recursive, and that nonemptiness of safety automata is decidable but not elementary. The proofs use nondeterministic tree automata with faulty counters. Allowing upward moves, leftward moves, or two registers, each causes undecidability. As corollaries, decidability is obtained for two data-sensitive fragments of the XPath query language.

Querying XML data sources that export very large sets of views

We study the problem of querying XML data sources that accept only a limited set of queries, such as sources accessible by Web services which can implement very large (potentially infinite) families of XPath queries. To compactly specify such families of queries we adopt the Query Set Specifications, a formalism close to context-free grammars. We say that query Q is expressible by the specification P if it is equivalent to some expansion of P. Q is supported by P if it has an equivalent rewriting using some finite set of P's expansions. We study the complexity of expressibility and support and identify large classes of XPath queries for which there are efficient (PTIME) algorithms. Our study considers both the case in which the XML nodes in the results of the queries lose their original identity and the one in which the source exposes persistent node ids.

Efficient Processing XPath Queries by Compressed XML Query Tree Based on Structural Index

As XPath is the core of most XML query languages, the efficiency of processing XPath expression has been a main part of the cost in XML queries. However, most existing XPath processing algorithms, which don't take index structure into account, spend lots of costs on spaces and time. This paper proposes an efficient XPath query processing mechanism based on structural index that makes full use of XML structural index to quickly retrieve XML data. Coming together with the mechanism, the Compressed XPath Query Tree based on structural index is proposed, which significantly reduces many join operations. Then query algorithms are used to deal with all the structural relationship using our mechanism. Finally, experiments will run the algorithm on real XML datasets and query workloads to report the performance of our mechanism and show the efficiency compared with other mechanisms.

An Efficient Middleware for Storing and Querying XML Data in Relational Database Management System

Problem statement: In this study, we propose a middleware that provides a transformation utility for storing and querying XML data in relational databases using model mapping method. Approach: To store XML documents in RDBMS, several mapping approaches can be used. We chose structure independent approach. In this middleware the model mapping method XParent and free of cost available technologies MYSQL, PhpMyAdmin and PHPclasses are used as examples. Results: This middleware stores XML tables and does not require a direct extension of SQL thus this middleware can be used with any relational databases management system with little changes in the middleware interface. The middleware offers two alternative methods -namely XParent and XReal- for storing XML in the database. Conclusion: The key to proposed middleware is to store XML document in a relational database through a user interface and with an XPath query processor. We present a comparative experimental study on the performance of insertion and retrieval of two types of XML documents with a set of XPath queries executed though the XPath. XML and Relational databases cannot be kept separately because XML is becoming the universal standard data format for the representation and exchanging the information whereas most existing data lies in RDBMS and their power of data capabilities cannot be degraded so the solution to this problem a middleware prototype is required. The proposed schema dependent solutions have a drawback that evens a small change in the logical structure of XML documents influence on the database schemas and several problems occur during the updating process. A new efficient data middleware is proposed in the study to face these issues.