17 research outputs found
Expressing OLAP operators with the TAX XML algebra
With the rise of XML as a standard for representing business data, XML data
warehouses appear as suitable solutions for Web-based decision-support
applications. In this context, it is necessary to allow OLAP analyses over XML
data cubes (XOLAP). Thus, XQuery extensions are needed. To help define a formal
framework and allow much-needed performance optimizations on analytical queries
expressed in XQuery, having an algebra at one's disposal is desirable. However,
XOLAP approaches and algebras from the literature still largely rely on the
relational model and/or only feature a small number of OLAP operators. In
opposition, we propose in this paper to express a broad set of OLAP operators
with the TAX XML algebra.Comment: in 3rd International Workshop on Database Technologies for Handling
XML Information on the Web (DataX-EDBT 08), Nantes : France (2008
Constructing Optimal Bushy Trees Possibly Containing Cross Products for Order Preserving Joins is in P
One of the main features of XQuery compared to traditional query languages like SQL, is that it preserves the input order - unless specified otherwise. As a consequence, order-preserving algebraic operators are needed to capture the semantics of XQuery correctly. One important algebraic operator is the order-preserving join. The order-preserving join is associative but, in contrast to the traditional join operator, not commutative. Since join ordering (i.e. finding the optimal execution plan for a given set of join operators) has been an important topic of query optimization for SQL, it is expected that it will also play a major role in optimizing XQuery. The search space for ordering traditional joins is exponential in size. Although the lack of commutativity reduces the search space for ordering order-preserving joins, we show that it is still exponential. This raises the question whether the join ordering problem is also NP-hard, as in the traditional setting. We answer this question by introducing the first polynomial algorithm that produces optimal bushy trees possibly containing cross products
On the Complexity of Nonrecursive XQuery and Functional Query Languages on Complex Values
This paper studies the complexity of evaluating functional query languages
for complex values such as monad algebra and the recursion-free fragment of
XQuery.
We show that monad algebra with equality restricted to atomic values is
complete for the class TA[2^{O(n)}, O(n)] of problems solvable in linear
exponential time with a linear number of alternations. The monotone fragment of
monad algebra with atomic value equality but without negation is complete for
nondeterministic exponential time. For monad algebra with deep equality, we
establish TA[2^{O(n)}, O(n)] lower and exponential-space upper bounds.
Then we study a fragment of XQuery, Core XQuery, that seems to incorporate
all the features of a query language on complex values that are traditionally
deemed essential. A close connection between monad algebra on lists and Core
XQuery (with ``child'' as the only axis) is exhibited, and it is shown that
these languages are expressively equivalent up to representation issues. We
show that Core XQuery is just as hard as monad algebra w.r.t. combined
complexity, and that it is in TC0 if the query is assumed fixed.Comment: Long version of PODS 2005 pape
A Modal Logical Approach for Developing XML Databases
This paper investigates the possibility of realizing the core of an XML
database system by a pure modal logical formalism providing query and
constraint languages with well-defined syntax semantics and computational
elements. The paper also introduces a domain-specific modal logic for XML
documents which can be used to implement some of the basic services of an
XML database
Regular Expression Types for XML
We propose regular expression types as a foundation for statically typed XML processing languages. Regular expression types, like most schema languages for XML, introduce regular expression notations such as repetition (*), alternation (|), etc., to describe XML documents. The novelty of our type system is a semantic presentation of subtyping, as inclusion between the sets of documents denoted by two types. We give several examples illustrating the usefulness of this form of subtyping in XML processing.
The decision problem for the subtype relation reduces to the inclusion problem between tree automata, which is known to be EXPTIME-complete. To avoid this high complexity in typical cases, we develop a practical algorithm that, unlike classical algorithms based on determinization of tree automata, checks the inclusion relation by a top-down traversal of the original type expressions. The main advantage of this algorithm is that it can exploit the property that type expressions being compared often share portions of their representations. Our algorithm is a variant of Aiken and Murphy\u27s set-inclusion constraint solver, to which are added several new implementation techniques, correctness proofs, and preliminary performance measurements on some small programs in the domain of typed XML processing
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A visual XML query interface
As XML becomes more and more popular, easy-to-use and powerful XML query languages are in great need. Xing is a visual query and restructuring language for XML documents. The objective of this project is to develop a basic version of Xing, including a user-oriented XML query interface and a simple query translation implementation. The interface design is based on a visual document metaphor and the notion of document patterns and rules. End users do not have to be good at programming or XML syntax to use Xing. In this report, we describe the implementation for the Xing prototype, including GUI design, data structures and algorithms. We also compare the features of Xing with other XML query languages
Fast Queries Over Heterogeneous Data Through Engine Customization
Industry and academia are continuously becoming more data-driven and data-intensive, relying on the analysis of a wide variety of heterogeneous datasets to gain insights. The different data models and formats pose a significant challenge on performing analysis over a combination of diverse datasets. Serving all queries using a single, general-purpose query engine is slow. On the other hand, using a specialized engine for each heterogeneous dataset increases complexity: queries touching a combination of datasets require an integration layer over the different engines. This paper presents a system design that natively supports heterogeneous data formats and also minimizes query execution times. For multi-format support, the design uses an expressive query algebra which enables operations over various data models. For minimal execution times, it uses a code generation mechanism to mimic the system and storage most appropriate to answer a query fast. We validate our design by building Proteus, a query engine which natively supports queries over CSV, JSON, and relational binary data, and which specializes itself to each query, dataset, and workload via code generation. Proteus outperforms state-of-the-art open-source and commercial systems on both synthetic and real-world workloads without being tied to a single data model or format, all while exposing users to a single query interface
TIMBER: A native XML database
This paper describes the overall design and architecture of the Timber XML database system currently being implemented at the University of Michigan. The system is based upon a bulk algebra for manipulating trees, and natively stores XML. New access methods have been developed to evaluate queries in the XML context, and new cost estimation and query optimization techniques have also been developed. We present performance numbers to support some of our design decisions. We believe that the key intellectual contribution of this system is a comprehensive set-at-a-time query processing ability in a native XML store, with all the standard components of relational query processing, including algebraic rewriting and a cost-based optimizer.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/42328/1/20110274.pd