barcode generator project source code in vb.net Choosing a Unique Identi er in Software

Create PDF 417 in Software Choosing a Unique Identi er

Choosing a Unique Identi er
PDF 417 Recognizer In None
Using Barcode Control SDK for Software Control to generate, create, read, scan barcode image in Software applications.
Encode PDF 417 In None
Using Barcode maker for Software Control to generate, create PDF-417 2d barcode image in Software applications.
The rst step in normalization is to choose a unique identi er, which is an attribute (column) or set of attributes that uniquely identi es each row of data in the relation.
Read PDF-417 2d Barcode In None
Using Barcode reader for Software Control to read, scan read, scan image in Software applications.
PDF-417 2d Barcode Generation In C#.NET
Using Barcode creator for .NET framework Control to generate, create PDF417 image in .NET framework applications.
Relational Database Concepts
PDF 417 Generation In .NET
Using Barcode maker for ASP.NET Control to generate, create PDF-417 2d barcode image in ASP.NET applications.
PDF 417 Printer In Visual Studio .NET
Using Barcode printer for Visual Studio .NET Control to generate, create PDF417 image in .NET applications.
The unique identi er will eventually become the primary key of the table created from the normalized relation. Normalization absolutely requires that a unique identi er be found for each relation. In many cases, a single attribute can be found that uniquely identi es the data in each row of the relation to be normalized. When no single attribute can be found to use for a unique identi er, you may be able to nd several attributes that can be concatenated (put together) in order to form the unique identi er. When unique identi ers are formed from multiple attributes, each attribute still remains in its own column you simply de ne the unique identi er as consisting of more than one column. In a few cases, there is no reasonable set of attributes in a relation that can be used as a unique identi er. When this occurs, you must invent a unique identi er, often with data values assigned sequentially or randomly as rows of data are added to the database table. This technique is the source of such unique identi ers as social security numbers, employee IDs, and vehicle identi cation numbers. The Movie relation in Figure 1-3 presents us with a bit of a poser in nding a unique identi er. At rst, it would seem that Movie ID would work just ne. However, notice that Movie ID values 2 and 3 appear twice each, so clearly it s not unique. The problem is that the Movie ID uniquely identi es each movie title, but the video store is keeping track of each copy of the movie they have in stock. This is because they rent movies and they want to be sure the renter returns the exact copy that they borrowed. After inspection of the sample data and some discussion with the store s manager, you conclude that there is no combination of attributes in the Movie relation that will uniquely identify each movie copy, so you invent an attribute called Copy Number that you can add to the relation. Whenever a unique identi er (or part of one) is invented, it is very important that everyone understands the values the unique identi er will assume. In this case, the store manager decided she wanted the Copy Number to start over for each Movie ID, which means the Copy Number is only unique when concatenated with Movie ID. The resulting relation is shown in Figure 1-4.
Generating PDF 417 In Visual Basic .NET
Using Barcode encoder for .NET Control to generate, create PDF-417 2d barcode image in .NET framework applications.
ECC200 Maker In None
Using Barcode maker for Software Control to generate, create DataMatrix image in Software applications.
First Normal Form: Eliminating Repeating Data
Encoding Code 3/9 In None
Using Barcode maker for Software Control to generate, create Code-39 image in Software applications.
Painting UPCA In None
Using Barcode generation for Software Control to generate, create UPC-A image in Software applications.
A relation is in rst normal form when it contains no multivalued attributes, which are attributes that have multiple values in the same row of data. Every intersection of a row and a column in a relation must contain at most one data value in order for the relation to be in rst normal form. In Figure 1-4, the language (Lang. Code) attribute contains multiple values for at least some movies, so you must consider it a multivalued attribute. Attributes in this form are more dif cult to maintain because the list of values must be picked apart so that individual values within the list may be changed while leaving other values in the list intact.
Encode UPC - 13 In None
Using Barcode encoder for Software Control to generate, create GTIN - 13 image in Software applications.
Barcode Generator In None
Using Barcode generation for Software Control to generate, create barcode image in Software applications.
Movie: MPAA MOVIE COPY GENRE GENRE LANG. RATING DESC. CODE ID NUMBER CODE CODE
USPS PLANET Barcode Drawer In None
Using Barcode encoder for Software Control to generate, create USPS Confirm Service Barcode image in Software applications.
UPC-A Supplement 5 Generation In Java
Using Barcode generation for Eclipse BIRT Control to generate, create Universal Product Code version A image in Eclipse BIRT applications.
SQL Demysti ed
Painting Barcode In Visual Studio .NET
Using Barcode encoder for Reporting Service Control to generate, create barcode image in Reporting Service applications.
UCC - 12 Decoder In C#.NET
Using Barcode recognizer for VS .NET Control to read, scan read, scan image in VS .NET applications.
1 Drama Drama
Painting GTIN - 13 In Objective-C
Using Barcode creation for iPhone Control to generate, create EAN 13 image in iPhone applications.
Data Matrix ECC200 Reader In .NET Framework
Using Barcode recognizer for .NET Control to read, scan read, scan image in VS .NET applications.
en, fr
Code 3 Of 9 Generation In Visual Studio .NET
Using Barcode encoder for Visual Studio .NET Control to generate, create Code39 image in Visual Studio .NET applications.
Make Bar Code In Java
Using Barcode creation for Android Control to generate, create barcode image in Android applications.
MPAA MOVIE YEAR DATE DATE MEDIA RETAIL RATING TITLE PRODUCED ACQUIRED SOLD FORMAT PRICE DESC. Under 17 requires accompanying parent or adult Mystic River 2003 1/1/2005 DVD 19.96 guardian Under 17 requires accompanying parent or adult The Last Samurai guardian Under 17 requires accompanying parent or adult The Last Samurai guardian Parents strongly cautioned Parents strongly cautioned Parents strongly cautioned Something s Gotta Give Something s Gotta Give The Italian Job
Copyright © OnBarcode.com . All rights reserved.