The expressive power of languages has been widely studied in Computer Science literature. In this... more The expressive power of languages has been widely studied in Computer Science literature. In this technical report we investigate the expressive power of XQuery, trying to focus on fragments of the language itself in order to outline which features are really necessary, and which ones simplify queries already expressible and could hence be omitted. The core of the report is the study of the effect of recursion, aggregates, sequence generators, node constructors, and position information on the expressiveness of XQuery, ...
Abstract In the relational model it has been shown that the flat relational algebra has the same ... more Abstract In the relational model it has been shown that the flat relational algebra has the same expressive power as the nested relational algebra, as far as queries over flat relations and with flat results are concerned [11]. Hence, for each query that uses the nested relational model and that, with a flat table as input always has a flat table as output, there exists an equivalent flat query that only uses the flat relational model. In [12] a very direct proof is given of this fact using a simulation technique.
Spatial databases are modeled as closed subsets of the real plane that canbe defined by a Boolean... more Spatial databases are modeled as closed subsets of the real plane that canbe defined by a Boolean system of polynomial inequalities (ie, as closedsemi-algebraic sets). First-order logic over the reals expanded with a binaryrelation symbol to address the spatial database provides a natural languagefor expressing properties of such databases. Such a spatial query languagefits in the (by now rather well-known) framework of constraint query languagesintroduced by Kanellakis, Kuper and Revesz [1]. Motivated by applications in ...
Not sure of the Publishers copyright policy to archiving your journal articles online? Use these ... more Not sure of the Publishers copyright policy to archiving your journal articles online? Use these sites to find a summary of permissions that are normally given as part of each publisher's copyright transfer agreement. ... Kuper, G. & Libkin, L. & Paredaens, J. (Ed.) Constraint Databases, p. 275-292. ... There are no files associated with this item. ... Items in DSpace are protected by copyright, with all rights reserved, unless otherwise indicated.
In the relational model it has been shown that the flat relational algebra has the same expressiv... more In the relational model it has been shown that the flat relational algebra has the same expressive power as the nested relational algebra, as far as queries over flat relations and with flat results are concerned [11]. Hence, for each query that uses the nested relational model and that, with a flat table as input always has a flat table as output, there exists an equivalent flat query that only uses the flat relational model. In [12] a very direct proof is given of this fact using a simulation technique. In analogy, we study a related flat- ...
Abstract: Semistructured databases require tailor-made concurrency control mechanisms since tradi... more Abstract: Semistructured databases require tailor-made concurrency control mechanisms since traditional solutions for the relational model have been shown to be inadequate. Such mechanisms need to take full advantage of the hierarchical structure of semistructured data, for instance allowing concurrent updates of subtrees of, or even individual elements in, XML documents. We present an approach for concurrency control which is document-independent in the sense that two schedules of semistructured transactions are ...
Foundations of Information and Knowledge Systems, 2010
XML is a modern format that is nowadays used to store many documents, expecially on the Web. Sinc... more XML is a modern format that is nowadays used to store many documents, expecially on the Web. Since a set of documents can be considered as a semi-structured dataset or database, we want to query these documents. Moreover in many applications we need to transform documents into other documents, containing the same information, but with a different structure. Finally, most documents are represented in HTML on the Web, which can be seen as XML-documents. We discuss sublanguages of XPath, XQuery and XSLT. The latter are ...
Proceedings of the Eleventh Italian Symposium on Advanced Database Systems (SEBD), 2003
Abstract. Semistructured databases require tailor-made concurrency control mechanisms since tradi... more Abstract. Semistructured databases require tailor-made concurrency control mechanisms since traditional solutions for the relational model have been shown to be inadequate. Such mechanisms need to take full advantage of the hierarchical structure of semistructured data, for instance allowing concurrent updates of subtrees of, or even individual elements in XML documents. In earlier work, we presented two equivalent path locking schemes and two schedulers which guarantee serializability of schedules on XML documents. However, ...
Recently proposed form-based web information systems liberate the capture and reuse of data in or... more Recently proposed form-based web information systems liberate the capture and reuse of data in organizations by substituting the development of technical implementations of electronic forms for the conceptual modelling of forms' tree-structured schemas and their data access rules. Significantly, these instance-dependent rules also imply a workflow process associated to a form, eliminating the need for a costly workflow design phase. Instead, the workflows thus created in an ad hoc manner by unsophisticated end-users ...
Current Trends in Database Technology–EDBT 2006, 2006
Since XML is used as a storage format in an increasing number of applications, security has becom... more Since XML is used as a storage format in an increasing number of applications, security has become an important issue in XML databases. One aspect of security is restricting access to data by certain users. This can, for example, be achieved by means of access rules or XML security views, which define projections over XML documents. The usage of security views avoids information leakage that may occur when we use certain access rules. XML views can be implemented by materialized views, but materialization and maintenance of views ...
We give a light-weight but formal introduction to XQuery by defining a sublanguage of XQuery. We ... more We give a light-weight but formal introduction to XQuery by defining a sublanguage of XQuery. We ignore typing, and don't consider namespaces, comments, programming instructions, and entities. To avoid confusion we call our version LiXQuery (Light XQuery). LiXQuery is fully downwards compatible with XQuery. Its syntax and its semantics are far less complex than that of XQuery, but the typical expressions of XQuery are included in LiXQuery. We claim that LiXQuery is an elegant and simple sublanguage of XQuery that ...
The hierarchical and semistructured nature of XML data may cause complicated update behavior. Upd... more The hierarchical and semistructured nature of XML data may cause complicated update behavior. Updates should not be limited to entire document trees, but should ideally involve subtrees and even individual elements. Providing a suitable scheduling algorithm for semistructured data can significantly improve collaboration systems that store their data—e.g., word processing documents or vector graphics—as XML documents. In this paper we show that concurrency control mechanisms in CVS, relational, and object-oriented database systems are inadequate for collaborative systems based on semistructured data. We therefore propose two new locking schemes based on path locks which are tightly coupled to the document instance. We also introduce two scheduling algorithms that can both be used with any of the two proposed path lock schemes. We prove that both schedulers guarantee serializability, and show that the conflict rules are necessary.
The expressive power of languages has been widely studied in Computer Science literature. In this... more The expressive power of languages has been widely studied in Computer Science literature. In this technical report we investigate the expressive power of XQuery, trying to focus on fragments of the language itself in order to outline which features are really necessary, and which ones simplify queries already expressible and could hence be omitted. The core of the report is the study of the effect of recursion, aggregates, sequence generators, node constructors, and position information on the expressiveness of XQuery, ...
Abstract In the relational model it has been shown that the flat relational algebra has the same ... more Abstract In the relational model it has been shown that the flat relational algebra has the same expressive power as the nested relational algebra, as far as queries over flat relations and with flat results are concerned [11]. Hence, for each query that uses the nested relational model and that, with a flat table as input always has a flat table as output, there exists an equivalent flat query that only uses the flat relational model. In [12] a very direct proof is given of this fact using a simulation technique.
Spatial databases are modeled as closed subsets of the real plane that canbe defined by a Boolean... more Spatial databases are modeled as closed subsets of the real plane that canbe defined by a Boolean system of polynomial inequalities (ie, as closedsemi-algebraic sets). First-order logic over the reals expanded with a binaryrelation symbol to address the spatial database provides a natural languagefor expressing properties of such databases. Such a spatial query languagefits in the (by now rather well-known) framework of constraint query languagesintroduced by Kanellakis, Kuper and Revesz [1]. Motivated by applications in ...
Not sure of the Publishers copyright policy to archiving your journal articles online? Use these ... more Not sure of the Publishers copyright policy to archiving your journal articles online? Use these sites to find a summary of permissions that are normally given as part of each publisher's copyright transfer agreement. ... Kuper, G. & Libkin, L. & Paredaens, J. (Ed.) Constraint Databases, p. 275-292. ... There are no files associated with this item. ... Items in DSpace are protected by copyright, with all rights reserved, unless otherwise indicated.
In the relational model it has been shown that the flat relational algebra has the same expressiv... more In the relational model it has been shown that the flat relational algebra has the same expressive power as the nested relational algebra, as far as queries over flat relations and with flat results are concerned [11]. Hence, for each query that uses the nested relational model and that, with a flat table as input always has a flat table as output, there exists an equivalent flat query that only uses the flat relational model. In [12] a very direct proof is given of this fact using a simulation technique. In analogy, we study a related flat- ...
Abstract: Semistructured databases require tailor-made concurrency control mechanisms since tradi... more Abstract: Semistructured databases require tailor-made concurrency control mechanisms since traditional solutions for the relational model have been shown to be inadequate. Such mechanisms need to take full advantage of the hierarchical structure of semistructured data, for instance allowing concurrent updates of subtrees of, or even individual elements in, XML documents. We present an approach for concurrency control which is document-independent in the sense that two schedules of semistructured transactions are ...
Foundations of Information and Knowledge Systems, 2010
XML is a modern format that is nowadays used to store many documents, expecially on the Web. Sinc... more XML is a modern format that is nowadays used to store many documents, expecially on the Web. Since a set of documents can be considered as a semi-structured dataset or database, we want to query these documents. Moreover in many applications we need to transform documents into other documents, containing the same information, but with a different structure. Finally, most documents are represented in HTML on the Web, which can be seen as XML-documents. We discuss sublanguages of XPath, XQuery and XSLT. The latter are ...
Proceedings of the Eleventh Italian Symposium on Advanced Database Systems (SEBD), 2003
Abstract. Semistructured databases require tailor-made concurrency control mechanisms since tradi... more Abstract. Semistructured databases require tailor-made concurrency control mechanisms since traditional solutions for the relational model have been shown to be inadequate. Such mechanisms need to take full advantage of the hierarchical structure of semistructured data, for instance allowing concurrent updates of subtrees of, or even individual elements in XML documents. In earlier work, we presented two equivalent path locking schemes and two schedulers which guarantee serializability of schedules on XML documents. However, ...
Recently proposed form-based web information systems liberate the capture and reuse of data in or... more Recently proposed form-based web information systems liberate the capture and reuse of data in organizations by substituting the development of technical implementations of electronic forms for the conceptual modelling of forms' tree-structured schemas and their data access rules. Significantly, these instance-dependent rules also imply a workflow process associated to a form, eliminating the need for a costly workflow design phase. Instead, the workflows thus created in an ad hoc manner by unsophisticated end-users ...
Current Trends in Database Technology–EDBT 2006, 2006
Since XML is used as a storage format in an increasing number of applications, security has becom... more Since XML is used as a storage format in an increasing number of applications, security has become an important issue in XML databases. One aspect of security is restricting access to data by certain users. This can, for example, be achieved by means of access rules or XML security views, which define projections over XML documents. The usage of security views avoids information leakage that may occur when we use certain access rules. XML views can be implemented by materialized views, but materialization and maintenance of views ...
We give a light-weight but formal introduction to XQuery by defining a sublanguage of XQuery. We ... more We give a light-weight but formal introduction to XQuery by defining a sublanguage of XQuery. We ignore typing, and don't consider namespaces, comments, programming instructions, and entities. To avoid confusion we call our version LiXQuery (Light XQuery). LiXQuery is fully downwards compatible with XQuery. Its syntax and its semantics are far less complex than that of XQuery, but the typical expressions of XQuery are included in LiXQuery. We claim that LiXQuery is an elegant and simple sublanguage of XQuery that ...
The hierarchical and semistructured nature of XML data may cause complicated update behavior. Upd... more The hierarchical and semistructured nature of XML data may cause complicated update behavior. Updates should not be limited to entire document trees, but should ideally involve subtrees and even individual elements. Providing a suitable scheduling algorithm for semistructured data can significantly improve collaboration systems that store their data—e.g., word processing documents or vector graphics—as XML documents. In this paper we show that concurrency control mechanisms in CVS, relational, and object-oriented database systems are inadequate for collaborative systems based on semistructured data. We therefore propose two new locking schemes based on path locks which are tightly coupled to the document instance. We also introduce two scheduling algorithms that can both be used with any of the two proposed path lock schemes. We prove that both schedulers guarantee serializability, and show that the conflict rules are necessary.
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