barcode generator in c# code project DATA REDUNDANCY AND DATABASE DESIGN in Font

Creator Denso QR Bar Code in Font DATA REDUNDANCY AND DATABASE DESIGN

CHAPTER 12 DATA REDUNDANCY AND DATABASE DESIGN
QR Code Generator In None
Using Barcode generation for Font Control to generate, create QR-Code image in Font applications.
www.OnBarcode.com
Denso QR Bar Code Maker In None
Using Barcode printer for Font Control to generate, create QR Code image in Font applications.
www.OnBarcode.com
TUPLE { S# S#('S1'), P# P#('P1'), QTY QTY(300) } TUPLE { SNO S#('S1'), PNO P#('P1'), AMT QTY(300) } These are clearly different tuples, but they both represent the same proposition: Supplier S1 supplies 300 of part P1. In fact, either of the two relvars SP and PS can be defined in terms of the other, as the following constraints both show:8 CONSTRAINT PS_SAME_AS_SP PS = SP RENAME ( S# AS SNO, P# AS PNO, QTY AS AMT ) ; CONSTRAINT SP_SAME_AS_PS SP = PS RENAME ( SNO AS S#, PNO AS P#, AMT AS QTY ) ; A database that contained both relvars would thus clearly involve some redundancy. Here s a simpler example to illustrate essentially the same point. Suppose we replace attribute CITY in the suppliers relvar S by two distinct attributes CITYA and CITYB, with the constraint that the CITYA and CITYB values are equal in every tuple (both of them representing the city for the applicable supplier). Here s a sample tuple: TUPLE { S# S#('S1'), SNAME NAME('Smith'), STATUS 20, CITYA 'London', CITYB 'London' } Then the following tuples both of them projections of the tuple just shown9 are certainly distinct, but they clearly represent the same proposition: TUPLE { S# S#('S1'), SNAME NAME('Smith'), STATUS 20, CITYA 'London' } TUPLE { S# S#('S1'), SNAME NAME('Smith'), STATUS 20, CITYB 'London' } Of course, the foregoing design would be extremely unlikely in practice. Note in particular that the principles of normalization militate against it; to be specific, the relvar satisfies the functional dependencies { CITYA } { CITYB } and { CITYB } { CITYA } and is thus not in 5NF (in fact, it isn t even in 3NF). But normalization per se doesn t solve the problem in this example (why not ), nor does it alter the fact that any number of distinct tuples can indeed represent the same proposition. Now, I said earlier that we can think of design theory as a set of principles and techniques for helping to pin down predicates (and hence constraints), and so it is. If we try to write down the predicate for the revised suppliers relvar (the one with attributes CITYA and CITYB), the fact that the design is bad becomes obvious:
Drawing Data Matrix In None
Using Barcode generation for Font Control to generate, create Data Matrix 2d barcode image in Font applications.
www.OnBarcode.com
GTIN - 12 Printer In None
Using Barcode drawer for Font Control to generate, create UPC-A Supplement 5 image in Font applications.
www.OnBarcode.com
8. By the way, note the relational comparisons in these constraints. How would you formulate them in SQL 9. Here I m overloading the projection operator by allowing it to apply to tuples as well as to relations (or relvars). I ll assume the availability of this tuple projection operator elsewhere in this chapter as well.
Creating USS Code 128 In None
Using Barcode printer for Font Control to generate, create ANSI/AIM Code 128 image in Font applications.
www.OnBarcode.com
Painting Barcode In None
Using Barcode printer for Font Control to generate, create Barcode image in Font applications.
www.OnBarcode.com
CHAPTER 12 DATA REDUNDANCY AND DATABASE DESIGN
Make UCC.EAN - 128 In None
Using Barcode creator for Font Control to generate, create EAN / UCC - 14 image in Font applications.
www.OnBarcode.com
Royal Mail Barcode Creation In None
Using Barcode printer for Font Control to generate, create British Royal Mail 4-State Customer Code image in Font applications.
www.OnBarcode.com
Supplier S# is under contract, is named SNAME, has status STATUS, is located in city CITYA, and is located in city CITYB. Here also, repeated, are the predicates for the two different shipments relvars SP and PS: Supplier S# supplies QTY of part P#. Supplier SNO supplies AMT of part PNO. These two examples suggest an obvious rule of thumb: When carrying out the initial design process in other words, when writing down the predicates or business rules always use the same name for the same property;10 don t play games by using both S# and SNO to refer to supplier numbers, QTY and AMT to refer to quantities, CITYA and CITYB to refer to cities, and so on. Following this rule will make it less likely that two distinct tuples will represent the same proposition.
Generate QR Code JIS X 0510 In None
Using Barcode generator for Font Control to generate, create QR Code JIS X 0510 image in Font applications.
www.OnBarcode.com
Generating QR Code JIS X 0510 In .NET
Using Barcode generation for .NET framework Control to generate, create QR Code ISO/IEC18004 image in Visual Studio .NET applications.
www.OnBarcode.com
Orthogonality (II)
Reading Barcode In Java
Using Barcode Control SDK for BIRT Control to generate, create, read, scan barcode image in BIRT applications.
www.OnBarcode.com
Decoding Barcode In .NET Framework
Using Barcode decoder for Visual Studio .NET Control to read, scan read, scan image in .NET applications.
www.OnBarcode.com
The net of the discussions in the previous section is that, in general, there s nothing like a oneto-one correspondence between tuples and propositions. Thus, we can t say categorically that the database involves some redundancy if and only if it contains two appearances of the same tuple. What we can say, however, is that if the database does contain two appearances of the same tuple, then there s at least a possibility maybe even a strong possibility, especially if the tuple in question is of degree greater than one11 that it involves some redundancy. In support of this claim, I observe that conventional normalization is precisely about eliminating redundant appearances of the same tuple. For example, suppose our usual suppliers relvar S is subject to an additional constraint to the effect that STATUS is functionally dependent on CITY: { CITY } { STATUS } Figure 12-7 shows a sample value for the relvar that conforms to this additional constraint (I ve changed the status of supplier S3 from 10 to 30 to make it do so).
Encoding UCC - 12 In Objective-C
Using Barcode creation for iPad Control to generate, create UCC - 12 image in iPad applications.
www.OnBarcode.com
Painting Barcode In None
Using Barcode encoder for Microsoft Excel Control to generate, create Barcode image in Excel applications.
www.OnBarcode.com
PDF417 Generator In .NET Framework
Using Barcode printer for Reporting Service Control to generate, create PDF 417 image in Reporting Service applications.
www.OnBarcode.com
Create Code 128A In Visual C#.NET
Using Barcode drawer for .NET framework Control to generate, create Code 128C image in .NET applications.
www.OnBarcode.com
Painting Barcode In Java
Using Barcode encoder for Android Control to generate, create Barcode image in Android applications.
www.OnBarcode.com
Generating ECC200 In Java
Using Barcode creator for Java Control to generate, create ECC200 image in Java applications.
www.OnBarcode.com
Making PDF417 In Java
Using Barcode generation for BIRT reports Control to generate, create PDF-417 2d barcode image in Eclipse BIRT applications.
www.OnBarcode.com
Data Matrix ECC200 Recognizer In None
Using Barcode decoder for Software Control to read, scan read, scan image in Software applications.
www.OnBarcode.com
Copyright © OnBarcode.com . All rights reserved.