No abstract
Hierarchical part-of relationships/aggregation structures and related queries are essential parts of information systems. However, relational database query languages do not explicitly support hierarchical relationships and queries. A hierarchical query may require a great number of join operations, which increases the effort in query formulation. Therefore, we propose path expressions in formulating hierarchical views over relational data because path expressions are a conventional and compact way to represent hierarchical relationships. We embed path expressions within SQL queries and compile them to standard SQL. This ensures that the path expressions can straightforwardly be implemented on the top of standard relational database systems. The compilation of a path expression is given by an attribute grammar, a conventional formalism to define the semantics of a language.
A search process is a ternary relationship between the user, the retrieval system and the user interface. A focused retrieval system aims at retrieving the most relevant parts within a relevant document. In focused retrieval the user interface may show not only the relevant documents but also identify the most relevant parts within a document. In document browsing a user may apply several strategies, related to the order of browsing, tolerance to irrelevance and the amount of required information. A model for result document browsing in focused retrieval is introduced. Further, its applicability is illustrated through a simulated experiment.
This article focuses on testing a path-oriented querying approach to hierarchical data in relational databases. The authors execute a user study to compare the path-oriented approach and traditional SQL from two perspectives: correctness of queries and time spent in querying. They also analyze what kinds of errors are typical in path-oriented SQL. Path-oriented query languages are popular in the context of object-orientation and XML. However, relational databases are the most common paradigm for storing data and SQL is most common for manipulating data. When querying hierarchical data in SQL, the user must specify join conditions explicitly between hierarchy levels. Path-oriented SQL is a new alternative for expressing hierarchical queries in relational databases. In the authors' study, the users spent significantly less time in writing path-oriented SQL queries and made fewer errors in query formulation.
Tampereen teknillinen yliopistoTiivistelmä Bagdad -matematiikkaa täältä ikuisuuteen on Ruotsalaisen Navet-tiedekeskuksen tuottama näyttely, joka pidettiin 11.4. -31.5.2013 Tampereen museokeskus Vapriikissa. Bagdad näyttely oli kiehtova matka matematiikan historiaan muutamine historian matemaatikoiden johdattamana. Al-Khwarizmi, Hypatia, Sonja Kovalevskaja, Arkhimedes, Brahmagupta ja muut matematiikan mestarit johdattivat yleisön matematiikan maailmaan draaman, pelien ja erilaisten pähkinöiden avulla. Jokainen näyttelykerta oli puolentoista tunnin mittainen ja piti sisällään johdannon, ryhmissä tehtävän ongelman, itsenäistä puuhastelua ja yhdessä tehtävän ongelman.Johdanto oli draamamuotoinen ja johdatteli yleisön matematiikan ongelmien pariin. Johdannon jälkeen ryhmissä tehtiin jokin matematiikan pulma tai ongelma. Tämän jälkeen yleisöllä oli mahdollisuus tutkia telttaa ja tutustua telttaan asetettuihin peleihin ja pulmiin itsenäisesti.Näyttelykerran lopussa yleisölle esitettiin yhteinen ongelma tai pulma ratkaistavaksi ja mietittäväksi.
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