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Prezentace Database_Tvaroh Tomáš

Y04A2L - Anglický jazyk 2-2

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Tomáš Tvaroh

General rules and principles in database design

There are different phases of database life cycle and each of them has different rules and principles according to the requirements on database. At first, database designer has to create a conceptual data model. It’s a very abstract and general model which contains entities and relations between them. It’s one of the most important parts of database life cycle, because if you design it incorrectly, then even if you handle the following parts well, your database will be flawed and it will be impossible to do something about it – only solution would be to start over. A standard set of rules defined by relational database guru Edgar F. Codd is known as a database normalization.
Database normalization is design method used to avoid data redundancies and logical inconsistencies in relational databases. Suppose you have a list of emploees where you keep their names, addresses and phone numbers (for example) and you want to make a list of tasks assigned to them. Creating another table, where would you have a name of the emploee and a description of the task, would be wrong, because you would have to keep the name of the emploee twice – in the assigned tasks list and in the list of employees. It’s not good for two reasons – the more data you keep the bigger the database gets and it results in less efficiency. Second reason is that if you, for example, want to change the description of the task, you would have to do it at more than one places, which is more complicated and more time-consuming, and sometimes, due to hardware malfunctions or power outage, some records remain unchanged and it re

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Vloženo: 28.04.2009

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