tailieunhanh - A Relational Model of Data for Large Shared Data Banks

In order to establish an accurate and up-to-date profile for ordinary UK adults and reflect trends in the profile of UK adults through 2009-11, researchers drew upon a range of sources including the British Household Panel Study, the DWP Financial Resources Survey (FRS), and the HM Revenue & Customs Marketable Wealth data. Based on this profile, a sample of 1,300 people deemed to be fully representative of UK adult population, up to and including the 95th percentile of savings wealth, is selected on a monthly basis by PureProfile, a leading online quantitative research panel. This sample includes approximately 1,000 savers (approximately. | Information Retrieval p. BAXENDALE Editor A Relational Model of Data for Large Shared Data Banks E. F. Codd IBM Research Laboratory San Jose California Future users of large data banks must be protected from having to know how the data is organized in the machine the internal representation . A prompting service which supplies such information is not a satisfactory solution. Activities of users at terminals and most application programs should remain unaffected when the internal representation of data is changed and even when some aspects of the external representation are changed. Changes in data representation will often be needed as a result of changes in query update and report traffic and natural growth in the types of stored information. Existing noninferential formatted data systems provide users with tree-structured files or slightly more general network models of the data. In Section 1 inadequacies of these models are discussed. A model based on n-ary relations a normal form for data base relations and the concept of a universal data sublanguage are introduced. In Section 2 certain operations on relations other than logical inference are discussed and applied to the problems of redundancy and consistency in the user s model. KEY WORDS AND PHRASES data bank data base data structure data organization hierarchies of data networks of data relations derivability redundancy consistency composition join retrieval language predicate calculus security data integrity CR CATEGORIES 1. Relational Model and Normal Form . Introduction This paper is concerned with the application of elementary relation theory to systems which provide shared access to large banks of formatted data. Except for a paper by Childs 1 the principal application of relations to data systems has been to deductive question-answering systems. Levein and Maron 2 provide numerous references to work in this area. In contrast the problems treated here are those of data .

• Ngân hàng - Tín dụng
• period leading
• Resistance and Targeting
• Progesterone Receptors
• Therapeutic Approach
• Approach to Endometriosis
• Endometriosis