Query Containment Research Articles

Scalable delivery of stream query result

Continuous queries over data streams typically produce large volumes of result streams. To scale up the system, one should carefully study the problem of delivering the result streams to the end users, which, unfortunately, is often overlooked in existing systems. In this paper, we leverage Distributed Publish/Subscribe System (DPSS), a scalable data dissemination infrastructure, for efficient stream query result delivery. To take advantage of DPSS's multicast-like data dissemination architecture, one has to exploit the common contents among different result streams and maximize the sharing of their delivery. Hence, we propose to merge the user queries into a few representative queries whose results subsume those of the original ones, and disseminate the result streams of these representative queries through the DPSS. To realize this approach, we study the stream query containment theories and propose efficient query grouping and merging algorithms. The proposed approach is non-intrusive and hence can be easily implemented as a middleware to be incorporated into existing stream processing systems. A prototype is developed on top of an open-source stream processing system and results of an extensive performance study on real datasets verify the efficacy of the proposed techniques.

대용량 RFID 데이터를 위한 효율적인 데이터 관리 기법

본 논문에서는 RFID 시스템에서 많이 발생하는 경로 질의와 포함 관계 질의를 효과적으로 처리하기 위한 데이터 관리 기법을 제안한다. 제안하는 데이터 관리 기법은 다양한 포함 관계에 대한 경로 정보를 유연하게 표현함으로써 운송 도중 발생하는 포함 관계의 변경 및 개별 단위의 물품 경로까지 지원한다. 또한, 공급망의 구조 정보를 활용한 경로 정보의 압축으로 저장되는 데이터의 양을 감소시킬 수 있다. 기존 기법들과 비교 평가를 수행한 결과 저장 공간과 질의 처리 측면에서 성능이 향상됨을 확인할 수 있었다. In this paper, we propose an efficient data management scheme for path queries and containment queries which are occurred frequently. The proposed data management scheme considers a change of the containment of products during a transport and supports a path of changed products by representing a path of various containments. Also, the compression utilizing the structure of supply chain reduces the stored data volumes. As a result, our method outperforms the existing methods in terms of storage efficiency and query processing time.

Efficient Data Management in RFID Applications

Logistics is in the limelight as one of a variety of RFID applications. The RFID technology is actively being applied to improve the competitiveness power of companies through the synthetic management of products and information. The RFID system generates large volume of stream data. It has problems which occur waste of storage and long processing time when storing large data and processing queries. Recently, many studies have been done to solve the problems which are generated in RFID system. In this thesis, we propose an efficient data management scheme for path queries and containment queries which are occurred frequently. The proposed data management scheme considers a change of the containment of products during a transport and supports a path of changed products by representing a path of various containments. Also, the compression utilizing the structure of supply chain reduces the stored data volumes. In order to show the superiority of our approach, we compare it with the existing schemes. As a result, our experimental results show that our scheme outperforms the existing scheme in terms of storage efficiency and query processing time.

A Decomposition Based Algorithm of Graph Containment Query

A Decomposition Based Algorithm of Graph Containment Query

Conjunctive query containment and answering under description logic constraints

Query containment and query answering are two important computational tasks in databases. While query answering amounts to computing 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 article, 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, for example, 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 is decidable, and analyze its computational complexity. We prove that query containment is undecidable in the case where we allow inequalities in the right-hand-side query, even for very simple constraints and queries. We show that query answering under description logic constraints can be reduced to query containment, and illustrate how such a reduction provides upper-bound results with respect to both combined and data complexity.

Efficient core computation in data exchange

Data exchange deals with inserting data from one database into another database having a different schema. Fagin et al. [2005] have shown that among the universal solutions of a solvable data exchange problem, there exists—up to isomorphism—a unique most compact one, “the core”, and have convincingly argued that this core should be the database to be materialized. They stated as an important open problem whether the core can be computed in polynomial time in the general setting where the mapping between the source and target schemas is given by source-to-target constraints that are arbitrary tuple generating dependencies (tgds) and target constraints consisting of equality generating dependencies (egds) and a weakly acyclic set of tgds. In this article, we solve this problem by developing new methods for efficiently computing the core of a universal solution. This positive result shows that data exchange based on cores is feasible and applicable in a very general setting. In addition to our main result, we use the method of hypertree decompositions to derive new algorithms and upper bounds for query containment checking and computing cores of arbitrary database instances. We also show that computing the core of a data exchange problem is fixed-parameter intractable with respect to a number of relevant parameters, and that computing cores is NP-complete if the rule bodies of target tgds are augmented by a special predicate that distinguishes a null value from a constant data value.

Containment of partially specified tree-pattern queries in the presence of dimension graphs

Nowadays, huge volumes of data are organized or exported in tree-structured form. Querying capabilities are provided through tree-pattern queries. The need for querying tree-structured data sources when their structure is not fully known, and the need to integrate multiple data sources with different tree structures have driven, recently, the suggestion of query languages that relax the complete specification of a tree pattern. In this paper, we consider a query language that allows the partial specification of a tree pattern. Queries in this language range from structureless keyword-based queries to completely specified tree patterns. To support the evaluation of partially specified queries, we use semantically rich constructs, called dimension graphs, which abstract structural information of the tree-structured data. We address the problem of query containment in the presence of dimension graphs and we provide necessary and sufficient conditions for query containment. As checking query containment can be expensive, we suggest two heuristic approaches for query containment in the presence of dimension graphs. Our approaches are based on extracting structural information from the dimension graph that can be added to the queries while preserving equivalence with respect to the dimension graph. We considered both cases: extracting and storing different types of structural information in advance, and extracting information on-the-fly (at query time). Both approaches are implemented, validated, and compared through experimental evaluation.

Deciding XPath containment with MSO

XPath is the standard language for addressing parts of an XML document. We present a sound and complete decision procedure for containment of XPath queries. The considered XPath fragment covers most of the language features used in practice. Specifically, we show how XPath queries can be translated into equivalent formulas in monadic second-order logic. Using this translation, we construct an optimized logical formulation of the containment problem, which is decided using tree automata. When the containment relation does not hold between two XPath expressions, a counter-example XML tree is generated. We provide practical experiments that illustrate the efficiency of the decision procedure for realistic scenarios.

A system for the static analysis of XPath

XPath is the standard language for navigating XML documents and returning a set of matching nodes. We present a sound and complete decision procedure for containment of XPath queries, as well as other related XPath decision problems such as satisfiability, equivalence, overlap, and coverage. The considered XPath fragment covers most of the language features used in practice. Specifically, we propose a unifying logic for XML, namely, the alternation-free modal μ-calculus with converse. We show how to translate major XML concepts such as XPath and regular XML types (including DTDs) into this logic. Based on these embeddings, we show how XPath decision problems, in the presence or absence of XML types, can be solved using a decision procedure for μ-calculus satisfiability. We provide a complexity analysis of our system together with practical experiments to illustrate the efficiency of the approach for realistic scenarios.

Kinetic sorting and kinetic convex hulls

Let S be a set of n points moving on the real line. The kinetic sorting problem is to maintain a data structure on the set S that makes it possible to quickly generate a sorted list of the points in S, at any given time. We prove tight lower bounds for this problem, which show the following: with a subquadratic maintenance cost one cannot obtain any significant speed-up on the time needed to generate the sorted list (compared to the trivial O ( n log n ) time), even for linear motions. We also describe a kinetic data structure for so-called gift-wrapping queries on a set S of n moving points in the plane: given a point q and a line ℓ through q such that all points from S lie on the same side of ℓ, report which point p i ∈ S is hit first when ℓ is rotated around q. Our KDS allows a trade-off between the query time and the maintenance cost: for any Q with 1 ⩽ Q ⩽ n , we can achieve O ( Q log n ) query time with a KDS that processes O ( n 2 + ϵ / Q 1 + 1 / δ ) events, where δ is the maximum degree of the polynomials describing the motions of the points. This allows us to reconstruct the convex hull quickly when the number of points on the convex hull is small. The structure also allows us to answer extreme-point queries (given a query direction d → , what is the point from S that is extreme in direction d → ?) and convex-hull containment queries (given a query point q, is q inside the current convex hull?).

Form-based proxy caching for database-backed web sites: keywords and functions

Web caching proxy servers are essential for improving web performance and scalability, and recent research has focused on making proxy caching work for database-backed web sites. In this paper, we explore a new proxy caching framework that exploits the query semantics of HTML forms. We identify two common classes of form-based queries from real-world database-backed web sites, namely, keyword-based queries and function-embedded queries. Using typical examples of these queries, we study two representative caching schemes within our framework: (i) traditional passive query caching, and (ii) active query caching, in which the proxy cache can service a request by evaluating a query over the contents of the cache. Results from our experimental implementation show that our form-based proxy is a general and flexible approach that efficiently enables active caching schemes for database-backed web sites. Furthermore, handling query containment at the proxy yields significant performance advantages over passive query caching, but extending the power of the active cache to do full semantic caching appears to be less generally effective.

Regular path queries under approximate semantics

We give a general framework for approximate query processing in semistructured databases. We focus on regular path queries, which are the integral part of most of the query languages for semistructured databases. To enable approximations, we allow the regular path queries to be distorted. The distortions are expressed in the system by using weighted regular expressions, which correspond to weighted regular transducers. After defining the notion of weighted approximate answers we show how to compute them in order of their proximity to the query. In the new approximate setting, query containment has to be redefined in order to take into account the quantitative proximity information in the query answers. For this, we define the approximate containment, and its variants k-containment and reliable contain-ment. Then, we give an optimal algorithm for deciding the k-containment. Regarding the reliable approximate containment, we show that it is polynomial time equivalent to the notorious limitedness problem in distance automata.

An efficient index structure for XML based on generalized suffix tree

A novel index structure based on the generalized suffix tree (PIGST) is proposed. Combined with post lists, PIGST can answer both structural and content queries. The distinct paths in an XML collection are mapped into strings. The construction algorithm of the PIGST for the path strings is presented based on the modification and improvement of a well-known suffix tree construction algorithm that only requires linear time and space complexity. The query process merely needs m character comparisons for direct containment queries, where m is the length of a query string. An efficient processing method for the indirect containment queries that avoids the inefficient tree traversal operation is also presented. Experiments show that PIGST outperforms earlier approaches.

Rewriting Union Queries Using Views

The problem of finding contained rewritings of queries using views is of great importance in mediated data integration systems. In this paper, we first present a general approach for finding contained rewritings of unions of conjunctive queries with arbitrary built-in predicates. Our approach is based on an improved method for testing conjunctive query containment in this context. Although conceptually simple, our approach generalizes previous methods for finding contained rewritings of conjunctive queries and is more powerful in the sense that many rewritings that can not be found using existing methods can be found by our approach. Furthermore, implication constraints (Zhang, X., & Ozsoyoglu, Z.M. (1997). Implication and referential constraints: A new formal resaoning. IEEE TKDE, 9(6):894--910, Now/Dec.) over the base relations can be easily handled. We then present a simplified approach which is less complete, but is much faster than the general approach, and it still finds maximum rewritings in several special cases. Our general approach finds more rewritings than previous algorithms such as the Bucket and the resolution-based algorithms. Our simplified approach generalizes the U-join and the MiniCon algorithms with no loss of efficiency.

Containment of aggregate queries

It is now common for databases to contain many gigabytes, or even many terabytes, of data. Scientific experiments in areas such as high energy physics produce data sets of enormous size, while in the business sector the emergence of decision-support systems and data warehouses has led organizations to build up gigantic collections of data. Aggregate queries allow one to retrieve concise information from such a database, since they can cover many data items while returning a small result. OLAP queries, used extensively in data warehousing, are based almost entirely on aggregation [4, 16]. Aggregate queries have also been studied in a variety of settings beyond relational databases, such as mobile computing [1], global information systems [21], stream data analysis [12], sensor networks [22] and constraint databases [2].

Decidable containment of recursive queries

One of the most important reasoning tasks on queries is checking containment, i.e., verifying whether one query yields necessarily a subset of the result of another one. Query containment is crucial in several contexts, such as query optimization, query reformulation, knowledge-base verification, information integration, integrity checking, and cooperative answering. Containment is undecidable in general for Datalog, the fundamental language for expressing recursive queries. On the other hand, it is known that containment between monadic Datalog queries and between Datalog queries and unions of conjunctive queries are decidable. It is also known that containment between unions of conjunctive two-way regular path queries, which are queries used in the context of semistructured data models containing a limited form of recursion in the form of transitive closure, is decidable. In this paper, we combine the automata-theoretic techniques at the base of these two decidability results to show that containment of Datalog in union of conjunctive two-way regular path queries is decidable in 2EXPTIME. By sharpening a known lower bound result for containment of Datalog in union of conjunctive queries we show also a matching lower bound.

Checking query containment with the CQC method

We present the Constructive Query Containment (CQC) method to check query containment and query containment under constraints for queries over databases with safe negation in both IDB and EDB subgoals and with or without built-in predicates. The aim of the CQC method is to construct a counterexample that proves that the query containment relationship being checked does not hold. The method uses different Variable Instantiation Patterns (VIPs) to generate only relevant counterexamples according to the syntactic properties of the queries and the databases considered in each test. The main contribution of the CQC method is threefold: it handles broader cases of queries and database schemas than most previous methods, it checks “true” containment instead of uniform containment (which is a sufficient but not necessary condition for containment) and it is not less efficient than other methods for the cases that they handle. Moreover, we prove also soundness and completeness of our method both for success and for failure.

Extraction itérative de requêtes fréquentes

Most approaches to knowledge discovery in databases consider extractions one at a time. However it is well known that, in practice, any extraction process is interactive and iterative. In this paper, we introduce an approach that can take benefit from previously computed extractions in the computation of the current extraction. To do so, we assume that the answers to previous extractions are stored and we use properties of query containment for pruning candidate queries. First, we introduce our approach in the context of deductive databases. Then, we show that restricting our framework to the case of relational queries allows for reducing the complexity of query containment tests. The experimental results reported in this paper show a significant reduction of computation time when taking into account the iterative aspects mentioned above.

XML 포함질의를 위한 확장형 인덱스

Containment queries for XML documents is one of the most important query types, and thus the efficient support for this type of query is crucial for XML databases. Recently, object-relational database management system (ORDBMS) vendors try to store and retrieve XML data in their products. In this paper, we propose an extensible index to support containment queries over the XML data stored as BLOB type in ORDBMSs. That is, we describe how to implement the index using the extensibility feature of an ORDBMS, and describe its usage.

Monadic datalog and the expressive power of languages for Web information extraction

Research on information extraction from Web pages (wrapping) has seen much activity recently (particularly systems implementations), but little work has been done on formally studying the expressiveness of the formalisms proposed or on the theoretical foundations of wrapping. In this paper, we first study monadic datalog over trees as a wrapping language. We show that this simple language is equivalent to monadic second order logic (MSO) in its ability to specify wrappers. We believe that MSO has the right expressiveness required for Web information extraction and propose MSO as a yardstick for evaluating and comparing wrappers. Along the way, several other results on the complexity of query evaluation and query containment for monadic datalog over trees are established, and a simple normal form for this language is presented. Using the above results, we subsequently study the kernel fragment Elog − of the Elog wrapping language used in the Lixto system (a visual wrapper generator). Curiously, Elog − exactly captures MSO, yet is easier to use. Indeed, programs in this language can be entirely visually specified.