Physical data independence

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  • Data Model: A set of concepts to describe the structure of a database, and certain constraints that the database should obey. Data Model Operations: Operations for specifying database retrievals and updates by referring to the concepts of the data model. Operations on the data model may include basic operations and user-defined operations.

    ppt34p thienthanoze 12-11-2012 51 7   Download

  • A crucial property of a relational DBMS is that it provides physical data independence. This allows physical structures such as indexes to change seamlessly without affecting the output of the query; but such changes do impact efficiency. Thus, together with the capabilities of the execution engine and the optimizer, the physical database design determines how efficiently a query is executed on a DBMS. The first generation of relational execution engines were relatively simple, targeted at OLTP, making index selection less of a problem.

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  • The minimum number of Cs that can be associated with one A is 1. I know this because the existence of the C to A relationship is mandatory. The maximum number of Cs that can be associated with one A is unlimited (or many). I know this because the cardinality of the C to A relationship is 1-M.

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  • Câu 1: A problem soling technique that decomposes a system its component parts while focusing on the business problem independent of technology is: a. Cause-and-effect analysis. b. System design. c. Joint application design(JAD). d. Systems analysis. Câu 2: A database is an organized collection of ____ related data. a. None of the others answers. b. logically. c. not. d. physically.

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  • We re-study the seven neutrino mass matrices with two independent vanishing entries under the latest results of neutrino oscillation experiments after the neutrino - 2012 conference. It is shown that the pattern B1 could be excluded since this pattern realizes very small value of mixing angle θ13. The remain six textures satisfy the current experimental data. We also find that all seven textures of neutrino mass matrix possess the normal hierarchy of neutrino mass spectrum.

    pdf8p thuyliebe 12-10-2018 7 0   Download

  • Our study described the prevalence of being bullied among students aged 13-17 and associated factors in this group in two districts in Nghe An Province in Vietnam in 2017. A cross-sectional study was performed with 1074 students. The study ananlyzed data from a survey about health risk behaviors and associated factors among school students. Its questionnaire was based on GSHS survey and Center for Epidemiological Studies-Depression scale. Students aged 13-17 in two schools, in urban and rural districts in Nghe An province, were selected for the research.

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  • The Indian Sundarbans is a coastal delta and major climate hotspot located in the state of West Bengal. The delta faces significant climatic challenges. The residents mainly depend on agriculture, livestock rearing and fishing. They face challenges of poverty, marginalization and an acute struggle against geo-climatic events. The present study was conducted to know the socio economic status of the farming community under the given resources viz. demographic, physical, economic, natural and social.

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  • The state of Meghalaya is blessed with abundant rainfall, fertile soil, diversity in natural resources and having a strong base in traditional knowledge, which have made it favorable for its Agricultural growth but still there is a decline in agricultural output. Land degradation due to loss of fertility and lots of other bio-physical and socio-economic causes paves the way for food insecurity, livelihood and affecting the economy of the state as a whole.

    pdf7p trinhthamhodang3 12-02-2020 3 0   Download



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