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Answering Queries Using Views: A Survey
, 2000
"... The problem of answering queries using views is to find efficient methods of answering a query using a set of previously defined materialized views over the database, rather than accessing the database relations. The problem has recently received significant attention because of its relevance to a w ..."
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Cited by 560 (32 self)
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The problem of answering queries using views is to find efficient methods of answering a query using a set of previously defined materialized views over the database, rather than accessing the database relations. The problem has recently received significant attention because of its relevance to a wide variety of data management problems. In query optimization, finding a rewriting of a query using a set of materialized views can yield a more efficient query execution plan. To support the separation of the logical and physical views of data, a storage schema can be described using views over the logical schema. As a result, finding a query execution plan that accesses the storage amounts to solving the problem of answering queries using views. Finally, the problem arises in data integration systems, where data sources can be described as precomputed views over a mediated schema. This article surveys the state of the art on the problem of answering queries using views, and synthesizes the disparate works into a coherent framework. We describe the different applications of the problem, the algorithms proposed to solve it and the relevant theoretical results.
Holistic twig joins: optimal XML pattern matching
- in: Proceedings of ACM SIGMOD International Conference on Management of Data, 2002
"... XML employs a tree-structured data model, and, naturally, XML queries specify patterns of selection predicates on multiple elements related by a tree structure. Finding all occurrences of such a twig pattern in an XML database is a core operation for XML query processing. Prior work has typically de ..."
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Cited by 346 (8 self)
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XML employs a tree-structured data model, and, naturally, XML queries specify patterns of selection predicates on multiple elements related by a tree structure. Finding all occurrences of such a twig pattern in an XML database is a core operation for XML query processing. Prior work has typically decomposed the twig pattern into binary structural (parent-child and ancestor-descendant) relationships, and twig matching is achieved by: (i) using structural join algorithms to match the binary relationships against the XML database, and (ii) stitching together these basic matches. A limitation of this approach for matching twig patterns is that intermediate result sizes can get large, even when the input and output sizes are more manageable. In this paper, we propose a novel holistic twig join algorithm, TwigStack, for matching an XML query twig pattern. Our technique uses a chain of linked stacks to compactly represent partial results to root-to-leaf query paths, which are then composed to obtain matches for the twig pattern. When the twig pattern uses only ancestor-descendant relationships between elements, TwigStack is I/O and CPU optimal among all sequential algorithms that read the entire input: it is linear in the sum of sizes of the input lists and the nal result list, but independent of the sizes of intermediate results. We then show how to use (a modication of) B-trees, along with TwigStack, to match query twig patterns in sub-linear time. Finally, we complement our analysis with experimental results on a range of real and synthetic data, and query twig patterns. 1
Storing and querying ordered xml using a relational database system
- In SIGMOD
, 2002
"... XML is quickly becoming the de facto standard for data exchange over the Intemet. This is creating a new set of data management requirements involving XML, such as the need to store and query XML documents. Researchers have proposed using relational database systems to satisfy these requirements by ..."
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Cited by 284 (3 self)
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XML is quickly becoming the de facto standard for data exchange over the Intemet. This is creating a new set of data management requirements involving XML, such as the need to store and query XML documents. Researchers have proposed using relational database systems to satisfy these requirements by devising ways to "shred " XML documents into relations, and translate XML queries into SQL queries over these relations. However, a key issue with such an approach, which has largely been ignored in the research literature, is how (and whether) the ordered XML data model can be efficiently supported by the unordered relational data model. This paper shows that XML's ordered data model can indeed be efficiently supported by a relational database system. This is accomplished by encoding order as a data value. We propose three order encoding methods that can be used to represent XML order in the relational data model, and also propose algorithms for translating ordered XPath expressions into SQL using these encoding methods. Finally, we report the results of an experimental study that investigates the performance of the proposed order encoding methods on a workload of ordered XML queries and updates. 1.
Structural Joins: A Primitive for Efficient XML Query Pattern Matching
- In ICDE
, 2002
"... XML queries typically specify patterns of selection predicates on multiple elements that have some specified tree structured relationships. The primitive tree structured relationships are parent-child and ancestor-descendant, and finding all occurrences of these structural relationships in an XML da ..."
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Cited by 279 (27 self)
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XML queries typically specify patterns of selection predicates on multiple elements that have some specified tree structured relationships. The primitive tree structured relationships are parent-child and ancestor-descendant, and finding all occurrences of these structural relationships in an XML database is a core operation for XML query processing. In this paper, we develop two families of structural join algorithms for this task: tree-merge and stack-tree. The tree-merge algorithms are a natural extension of traditional merge joins and the recently proposed multi-predicate merge joins, while the stack-tree algorithms have no counterpart in traditional relational join processing. We present experimental results on a range of data and queries using (i) the Timber native XML query engine built on top of SHORE, and (ii) a commercial relational database system. In all cases, our structural join algorithms turn out to be vastly superior to traditional traversal-style algorithms. Structural join algorithms are also much more efficient than using traditional join algorithms, implemented in relational databases, for the same task. Finally, we show that while, in some cases, tree-merge algorithms can have performance comparable to stack-tree algorithms, in many cases they are considerably worse. This behavior is explained by analytical results that demonstrate that, on sorted inputs, the stack-tree algorithms have worst-case I/O and CPU complexities linear in the sum of the sizes of inputs and output, while the tree-merge algorithms do not have the same guarantee.
XMill: an Efficient Compressor for XML Data
, 1999
"... We describe a tool for compressing XML data, with applications in data exchange and archiving, which usually achieves about twice the compression ratio of gzip at roughly the same speed. The compressor, called XMill, incorporates and combines existing compressors in order to apply them to heterogene ..."
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Cited by 229 (0 self)
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We describe a tool for compressing XML data, with applications in data exchange and archiving, which usually achieves about twice the compression ratio of gzip at roughly the same speed. The compressor, called XMill, incorporates and combines existing compressors in order to apply them to heterogeneous XML data: it uses zlib, the library function for gzip, a collection of datatype specific compressors for simple data types, and, possibly, user defined compressors for application specific data types. 1 Introduction We have implemented a compressor/decompressor for XML data, to be used in data exchange and archiving, that achieves about twice the compression rate of general-purpose compressors (gzip), at about the same speed. The tool can be downloaded from www.research.att.com/sw/tools/xmill/. XML is now being adopted by many organizations and industry groups, like the healthcare, banking, chemical, and telecommunications industries. The attraction in XML is that it is a self-describi...
Scalable semantic web data management using vertical partitioning
- In VLDB
, 2007
"... The dataset used for this benchmark is taken from the publicly available Barton Libraries dataset [1]. This data is provided by the Simile Project [3], which develops tools for library data management and interoperability. The data contains records that compose an RDF-formatted dump of the MIT Libra ..."
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Cited by 190 (6 self)
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The dataset used for this benchmark is taken from the publicly available Barton Libraries dataset [1]. This data is provided by the Simile Project [3], which develops tools for library data management and interoperability. The data contains records that compose an RDF-formatted dump of the MIT Libraries Barton catalog, converted from raw data stored in an old library format standard called MARC (Machine Readable Catalog). Because of the multiple sources the data was derived from and the diverse nature of the data that is cataloged, the structure of the data is quite irregular. At the time of publication of this report, there are slightly more than 50 million triples in the dataset, with a total of 221 unique properties, of which the vast majority appear infrequently. Of these properties, 82 (37%) are multi-valued, meaning that they appear more than once for a given subject; however, these properties appear more often (77 % of the triples have a multi-valued property). The dataset provides a good demonstration of the relatively unstructured nature of Semantic Web data. 2. LONGWELL OVERVIEW Longwell [2] is a tool developed by the Simile Project, which provides a graphical user interface for generic RDF data exploration in a web browser. It begins by presenting the user with a list of the values the type property can take (such as Text or Notated Music in the library dataset). The user can click on the types of data he desires to further explore. Longwell shows the list of currently filtered resources (RDF subjects) in the main portion of the screen, and a list of filters in panels along the side. Each panel represents a property that is defined on the current filter, with popular object values for that property and their frequency also presented in this box. If the user selects an object value, this filters the working set of resources to those that have that property-object value defined,
Updating XML
- In SIGMOD
, 2001
"... As XML has developed over the past few years, its role has expanded beyond its original domain as a semantics-preserving markup language for online documents, and it is now also the de facto format for interchanging data between heterogeneous systems. Data sources export XML "views" over t ..."
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Cited by 180 (4 self)
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As XML has developed over the past few years, its role has expanded beyond its original domain as a semantics-preserving markup language for online documents, and it is now also the de facto format for interchanging data between heterogeneous systems. Data sources export XML "views" over their data, and other systems can directly import or query these views. As a result, there has been great interest in languages and systems for expressing queries over XML data, whether the XML is stored in a repository or generated as a view over some other data storage format.
A vision for management of complex models
- SIGMOD Record
, 2000
"... Many problems encountered when building applications of database systems involve the manipulation of models. By “model, ” we mean a complex structure that represents a design artifact, such as a relational schema, object-oriented interface, UML model, XML DTD, web-site schema, semantic network, comp ..."
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Cited by 172 (23 self)
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Many problems encountered when building applications of database systems involve the manipulation of models. By “model, ” we mean a complex structure that represents a design artifact, such as a relational schema, object-oriented interface, UML model, XML DTD, web-site schema, semantic network, complex document, or software configuration. Many uses of models involve managing changes in models and transformations of data from one model into another. These uses require an explicit representation of “mappings ” between models. We propose to make database systems easier to use for these applications by making “model ” and “model mapping ” first-class objects with special operations that simplify their use. We call this capability model management. In addition to making the case for model management, our main contribution is a sketch of a proposed data model. The data model consists of formal, object-oriented structures for representing models and model mappings, and of high-level algebraic operations on those structures, such as matching, differencing, merging, function application, selection, inversion and instantiation. We focus on structure and semantics, not implementation. 1
Storing and Querying XML Data using an RDMBS
- IEEE Data Engineering Bulletin
, 1999
"... XML is rapidly becoming a popular data format. It can be expected that soon large volumes of XML data will exist. XML data is either produced manually (like html documents today), or it is generated by a new generation of software tools for the WWW and/or electronic data interchange (EDI). The purpo ..."
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Cited by 171 (5 self)
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XML is rapidly becoming a popular data format. It can be expected that soon large volumes of XML data will exist. XML data is either produced manually (like html documents today), or it is generated by a new generation of software tools for the WWW and/or electronic data interchange (EDI). The purpose of this paper is to present the results of an initial study about storing and querying XML data. As
A Normal Form for XML Documents
"... This paper takes a rst step towards the design and normalization theory for XML documents. We show that, like relational databases, XML documents may contain redundant information, and may be prone to update anomalies. Furthermore, such problems are caused by certain functional dependencies among p ..."
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Cited by 166 (8 self)
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This paper takes a rst step towards the design and normalization theory for XML documents. We show that, like relational databases, XML documents may contain redundant information, and may be prone to update anomalies. Furthermore, such problems are caused by certain functional dependencies among paths in the document. Our goal is to nd a way of converting an arbitrary DTD into a well-designed one, that avoids these problems. We rst introduce the concept of a functional dependency for XML, and de ne its semantics via a relational representation of XML. We then de ne an XML normal form, XNF, that avoids update anomalies and redundancies. We study its properties and show that it generalizes BCNF and a normal form for nested relations when those are appropriately coded as XML documents. Finally, we present a lossless algorithm for converting any DTD into one in XNF.
