Basic_Concepts_Databases_2nd_Part

Basic_Concepts_Databases_2nd_Part - Databases Using MS...

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Virginia Tech (copyright A.A. Trani) Databases Using MS Access Drs. A. A. Trani and D. Gallagher Dept. of Civil and Environmental Engineering
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Virginia Tech (copyright A.A. Trani) Why Learn M.S. Access? Learn to manipulate large datasets Lear the basics of relational databases Engineers need to manipulate large amounts of data Data sometimes comes in a variety of formats Data is both numeric and character or “string” data MS Access is part of the Office suite that you already have in your computer 2
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Virginia Tech (copyright A.A. Trani) Relational Structure l Data is organized into independent 2- dimensional arrays (or a table) l No formal linkages required between arrays l Easy to modify the structure of a 2-D table l Theoretically least complex and most intuitive structure for user l However: 2-dimensional tables can be very large and cumbersome to manipulate l Moreover, real world data comes from different sources and thus creating relationships between data sets
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Virginia Tech (copyright A.A. Trani) Basic Elements of Relational Database Table: columns rows Database: collection of tables
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Virginia Tech (copyright A.A. Trani) Alternative Relational Terms Used in Textbooks or in the Database Literature table = relation = array row = record = tuple column = feld = attribute
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Virginia Tech (copyright A.A. Trani) Table Concepts l Table may have a name intended to convey the meaning of the table as a whole l Size of table refers to the number of rows l Degree of table refers to the number of columns l The order of the rows or columns is not important (as long as we keep headings with columns). i.e. a sorted table is considered the same table l Often denoted by table name with attributes BOOK (ISBN,Title,Price)
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Virginia Tech (copyright A.A. Trani) Relationship Between Multiple Tables in Relational DBMS
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Virginia Tech (copyright A.A. Trani) Design Principles for Relational Database l Required key fields l Normalization first normal form second normal form third normal form
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Virginia Tech (copyright A.A. Trani) Key Field l A key is a field or combination of fields that uniquely identify each record l Duplicate entries in key fields are not allowed within a table l It is good practice, and often required, for each table to have key field(s) l examples single key field: unique ID sample number multiple key field: date + time + location + pollutant
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Virginia Tech (copyright A.A. Trani) Keys l Set of attributes that uniquely defines any entity from among all possible entities in the entity class that may appear in the database is called a superkey. Ex: ISBN l Superkeys can contain more attributes than absolutely necessary, e.g. SSN and LastName for USCitizen class l Key is minimal superkey, e.g SSN
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Virginia Tech (copyright A.A. Trani) Entity-Relationship Diagram
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This note was uploaded on 01/01/2012 for the course CEE 3804 taught by Professor Aatrani during the Spring '07 term at Virginia Tech.

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Basic_Concepts_Databases_2nd_Part - Databases Using MS...

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