Strong functional dependencies and their application to normal forms in XML.

"... This paper reviews the recent developments in specification languages, static and run-time analyses as well as applications of integrity constraints for XML. 1 ..."

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This paper reviews the recent developments in specification languages, static and run-time analyses as well as applications of integrity constraints for XML. 1

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On Codd Families of Keys over Incomplete Relations

by Sven Hartmann, Uwe Leck, Sebastian Link , 2010

"... Keys allow a database management system to uniquely identify tuples in a database. Consequently, the class of keys is of great significance for almost all data processing tasks. In the relational model of data, keys have received considerable interest and are well understood. However, for efficient ..."

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Keys allow a database management system to uniquely identify tuples in a database. Consequently, the class of keys is of great significance for almost all data processing tasks. In the relational model of data, keys have received considerable interest and are well understood. However, for efficient means of data processing most commercial relational database systems deviate from the relational model. For example, tuples may contain only partial information in the sense that they contain so-called null values to represent incomplete information. Codd’s principle of entity integrity says that every tuple of every relation must not contain a null value on any attribute of the primary key. Therefore, a key over partial relations enforces both uniqueness and totality of tuples on the attributes of the key. On the basis of these two requirements, we study the resulting class of keys over relations that permit occurrences of Zaniolo’s null value ‘no-information’. We show that the interaction of this class of keys is different from the interaction of the class of keys over total relations. We establish a finite ground axiomatization, and an algorithm for deciding the associated implication problem in linear time. Further, we characterize Armstrong relations for an arbitrarily given sets of keys; that is, we give a sufficient and necessary condition for a partial relation to satisfy a key precisely when it is implied by a given set of keys. We also establish an algorithm that computes an Armstrong relation

Efficient discovery of xml data redundancies

by Cong Yu - In VLDB , 2006

"... As XML becomes widely used, dealing with redundancies in XML data has become an increasingly important issue. Redundantly stored information can lead not just to a higher data storage cost, but also to increased costs for data transfer and data manipulation. Furthermore, such data redundancies can l ..."

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As XML becomes widely used, dealing with redundancies in XML data has become an increasingly important issue. Redundantly stored information can lead not just to a higher data storage cost, but also to increased costs for data transfer and data manipulation. Furthermore, such data redundancies can lead to potential update anomalies, rendering the database inconsistent. One way to avoid data redundancies is to employ good schema design based on known functional dependencies. In fact, several recent studies have focused on defining the notion of XML Functional Dependencies (XML FDs) to capture XML data redundancies. We observe further that XML databases are often “casually designed ” and XML FDs may not be determined in advance. Under such circumstances, discovering XML data redundancies (in terms of FDs) from the data itself becomes necessary and is an integral part of the schema refinement process. In this paper, we present the design and implementation of the first system, DiscoverXFD, for efficient discovery of XML data redundancies. It employs a novel XML data structure and introduces a new class of partition based algorithms. DiscoverXFD can not only be used for the previous definitions of XML functional dependencies, but also for a more comprehensive notion we develop in this paper, capable of detecting redundancies involving set elements while maintaining clear semantics. Experimental evaluations using real life and benchmark datasets demonstrate that our system is practical and scales well with increasing data size. 1.

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Generating Compact Redundancy-Free XML Documents from Conceptual-Model Hypergraphs

by Wai Yin Mok, David W. Embley - IEEE TRANSACTIONS ON KNOWLEDGE AND DATA ENGINEERING , 2006

"... As XML data becomes more and more prevalent and as larger quantities of data find their way into XML documents, the need for quality XML data organization will only increase. One standard way of structuring data well is to reduce and, if possible, eliminate redundancy, while at the same time makin ..."

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As XML data becomes more and more prevalent and as larger quantities of data find their way into XML documents, the need for quality XML data organization will only increase. One standard way of structuring data well is to reduce and, if possible, eliminate redundancy, while at the same time making the storage structures as compact as possible. In this paper, we present a methodology to generate XML storage structures where conforming XML documents are redundancy-free, and for most practical cases, are also fully compact. Our methodology assumes the input is a conceptual-model hypergraph. For the special case that every edge in the hypergraph is binary, we present a simple algorithm, guaranteed to always generate redundancy-free storage structures. We show, however, that generating a minimum number of redundancy-free storage structures is NP-hard. We therefore provide heuristics to guide the process and observe that these heuristics result in satisfactory solutions, which are often optimal. We then present a general algorithm for n-ary edges and show that it generates redundancy-free storage structures. The general algorithm must overcome several problems that do not arise in the special case.

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Unlocking keys for XML trees

by Sven Hartmann, Sebastian Link - ICDT 2007. LNCS , 2007

"... We review key constraints in the context of XML as introduced by Buneman et al. We show that one of the proposed inference rules is not sound in general, and the axiomatisation proposed for XML keys is incomplete even if key paths are simple. Therefore, the axiomatisation and also the implication pr ..."

Abstract - Cited by 11 (6 self) - Add to MetaCart

We review key constraints in the context of XML as introduced by Buneman et al. We show that one of the proposed inference rules is not sound in general, and the axiomatisation proposed for XML keys is incomplete even if key paths are simple. Therefore, the axiomatisation and also the implication problem for XML keys are still unsolved. We propose a set of inference rules that is indeed sound and complete for the implication of XML keys with simple key paths. Our completeness proof enables us to characterise the implication of XML keys in terms of the reachability problem of nodes in a digraph. This results in a quadratic time algorithm for deciding XML key implication, and shows that reasoning for XML keys is practically efficient.

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When data dependencies over SQL tables meet the Logics of Paradox and S-3

by Sven Hartmann, Sebastian Link - In Proceedings of the 29th ACM SIGMOD-SIGART-SIGACT Symposium on Principles of Database Systems (PoDS). ACM

"... We study functional and multivalued dependencies over SQL tables with NOT NULL constraints. Under a no-information interpretation of null values we develop tools for reason-ing. We further show that in the absence of NOT NULL constraints the associated implication problem is equivalent to that in pr ..."

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We study functional and multivalued dependencies over SQL tables with NOT NULL constraints. Under a no-information interpretation of null values we develop tools for reason-ing. We further show that in the absence of NOT NULL constraints the associated implication problem is equivalent to that in propositional fragments of Priest’s paraconsistent Logic of Paradox. Subsequently, we extend the equivalence to Boolean dependencies and to the presence of NOT NULL constraints using Schaerf and Cadoli’s S-3 logics where S corresponds to the set of attributes declared NOT NULL. The findings also apply to Codd’s interpretation “value at present unknown”utilizing a weak possible world semantics. Our results establish NOT NULL constraints as an effective mechanism to balance the expressiveness and tractability of consequence relations, and to control the degree by which the existing classical theory of data dependencies can be soundly approximated in practice.

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Design by example for SQL table definitions with functional dependencies

by Sven Hartmann, Markus Kirchberg, Sebastian Link - THE VLDB JOURNAL , 2011

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Normalization Theory for XML

by Marcelo Arenas

"... Since the beginnings of the relational model, it was clear for the database community that the process of designing a database is a nontrivial and timeconsuming ..."

Abstract - Cited by 7 (0 self) - Add to MetaCart

Since the beginnings of the relational model, it was clear for the database community that the process of designing a database is a nontrivial and timeconsuming

Strong functional dependencies and their application to normal forms in XML. (2004)

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