barcode generator dll c# WHAT FIRST NORMAL FORM REALLY MEANS in Font

Make QR Code in Font WHAT FIRST NORMAL FORM REALLY MEANS

CHAPTER 8 WHAT FIRST NORMAL FORM REALLY MEANS
QR-Code Drawer In None
Using Barcode creator for Font Control to generate, create Denso QR Bar Code image in Font applications.
www.OnBarcode.com
Code 39 Drawer In None
Using Barcode maker for Font Control to generate, create Code 39 Extended image in Font applications.
www.OnBarcode.com
Now, one reason I ve discussed these old arguments against hierarchies at such length is that we re starting to see a variety of newer hierarchic DBMSs emerge in the marketplace, and all of those old arguments apply directly to those newer systems. Examples of such systems include XML DBMSs, object-oriented DBMSs, and multi-value DBMSs. In all of these cases, the fundamental data object is hierarchic in nature and can be regarded at least to a first approximation as a table with RVAs.8 And I m well aware that there are those who would use this fact, and the arguments of this chapter, to buttress claims to the effect that relational systems are inadequate, or that hierarchic designs are a good idea, or that multi-value systems are really true relational systems (or worse! extended relational systems), and so on and so forth. So I want to confront such claims head on: First, as I ve tried to show, hierarchic designs are usually not a good idea anyway. Second, even if we do agree to regard those hierarchic data objects as tables (albeit ones that include RVAs), it doesn t follow that the system is relational! The point cannot be emphasized too strongly that tables alone do not a relational system make. Rather, we need support for everything else in the relational model as well, including in particular support for all of the operators of the relational algebra. Note: In this regard, it s worth pointing out that the ability to form, say, a join of two tables over some RVA requires support for relational comparisons e.g., the ability to test whether two relations are equal or whether one is a subset of the other and even SQL doesn t provide any such support at the time of writing (though Tutorial D does). It s also worth pointing out that there are some things we certainly don t want in a relational system: for example, user-visible pointers or object IDs, which many of those hierarchic systems most definitely do support.
Create QR Code In None
Using Barcode creation for Font Control to generate, create QR Code JIS X 0510 image in Font applications.
www.OnBarcode.com
EAN / UCC - 13 Generation In None
Using Barcode generation for Font Control to generate, create USS-128 image in Font applications.
www.OnBarcode.com
Relation-Valued Attributes in Base Tables The Good News
USS Code 128 Drawer In None
Using Barcode drawer for Font Control to generate, create Code 128 Code Set B image in Font applications.
www.OnBarcode.com
Making Data Matrix 2d Barcode In None
Using Barcode creation for Font Control to generate, create ECC200 image in Font applications.
www.OnBarcode.com
For reasons such as those articulated in the previous section, RVAs in base tables are usually contraindicated. Usually, but not always there are cases, albeit comparatively rare ones perhaps, where a base table with an RVA is exactly the right design. One simple example, table T7, is shown in Figure 8-7. The intended meaning of the table is that the persons identified within any given PERSONS value are all siblings of one another (and have no other siblings). Thus, Amy and Bob are siblings; Cal, Don, and Eve are siblings; and Fay is an only child. Note that the table has just one column (an RVA) and three rows. Note too that the sole key involves an RVA!9
UPC-A Supplement 5 Encoder In None
Using Barcode drawer for Font Control to generate, create GS1 - 12 image in Font applications.
www.OnBarcode.com
Create UPC - 8 In None
Using Barcode generation for Font Control to generate, create GS1 - 8 image in Font applications.
www.OnBarcode.com
8. Please note that phrase at least to a first approximation. The truth is, to suggest that the hierarchies in such systems might be regarded as tables with RVAs is extremely charitable to the systems concerned! See Appendix D for further discussion. 9. The following remark from Codd s 1970 paper is interesting in the light of this observation: The writer knows of no application that would require some key to have a relation-valued component. (I ve reworded the original just slightly here.)
Encode QR-Code In Java
Using Barcode creation for Android Control to generate, create Denso QR Bar Code image in Android applications.
www.OnBarcode.com
Making QR Code 2d Barcode In Visual Studio .NET
Using Barcode encoder for .NET framework Control to generate, create Denso QR Bar Code image in .NET framework applications.
www.OnBarcode.com
CHAPTER 8 WHAT FIRST NORMAL FORM REALLY MEANS
DataMatrix Drawer In Java
Using Barcode generation for Java Control to generate, create Data Matrix ECC200 image in Java applications.
www.OnBarcode.com
Barcode Generator In VS .NET
Using Barcode generation for Reporting Service Control to generate, create Barcode image in Reporting Service applications.
www.OnBarcode.com
7
Encoding QR Code In Java
Using Barcode creator for Java Control to generate, create QR-Code image in Java applications.
www.OnBarcode.com
QR Creator In .NET
Using Barcode generation for ASP.NET Control to generate, create QR Code image in ASP.NET applications.
www.OnBarcode.com
3(56216 6,% $P\ %RE 
Code 128C Drawer In None
Using Barcode creation for Online Control to generate, create Code 128 Code Set C image in Online applications.
www.OnBarcode.com
Barcode Generator In Visual C#.NET
Using Barcode drawer for VS .NET Control to generate, create Barcode image in VS .NET applications.
www.OnBarcode.com
 6,% &DO 'RQ (YH 
PDF417 Scanner In .NET Framework
Using Barcode recognizer for Visual Studio .NET Control to read, scan read, scan image in .NET framework applications.
www.OnBarcode.com
EAN13 Drawer In None
Using Barcode drawer for Microsoft Excel Control to generate, create UPC - 13 image in Microsoft Excel applications.
www.OnBarcode.com
 6,% )D\
Create 1D In VB.NET
Using Barcode creation for VS .NET Control to generate, create Linear Barcode image in Visual Studio .NET applications.
www.OnBarcode.com
UPC-A Creator In Java
Using Barcode printer for Java Control to generate, create UPC-A Supplement 2 image in Java applications.
www.OnBarcode.com
7
)$0,/< 0R]DUW 0R]DUW :DOWRQ :DOWRQ :DOWRQ 'YRUDN
6,% $P\ %RE &DO 'RQ (YH )D\
CHAPTER 8 WHAT FIRST NORMAL FORM REALLY MEANS
Now, you might think the foregoing example is a little contrived. Myself, I rather like it, because it illustrates the point I wanted to make namely, that RVAs can sometimes be useful, even in base tables without dragging in any issues that are irrelevant to that main point. Be that as it may, let me now bolster my argument with what some people might feel is a more realistic example. Figure 8-9 shows part of a catalog table T9 that documents the tables in the database and their keys (I m assuming that one of those tables is called MARRIAGE, and it has columns HUSBAND, WIFE, and wedding DATE; I m also assuming that the MARRIAGE table has three keys, each involving two of those three columns). Attribute KEY of table T9 is relation-valued.
7
7$%/( 0$55,$*(
.(< &2/801 +86%$1' '$7(
0$55,$*(
&2/801 '$7( :,)(
0$55,$*(
&2/801 :,)( +86%$1'
Copyright © OnBarcode.com . All rights reserved.