barcode fonts for excel 2010 free representing the relationship between students in Software

Creation Denso QR Bar Code in Software representing the relationship between students

representing the relationship between students
Creating Quick Response Code In None
Using Barcode drawer for Software Control to generate, create QR Code image in Software applications.
Decode QR Code JIS X 0510 In None
Using Barcode recognizer for Software Control to read, scan read, scan image in Software applications.
and textbooks If any o f the binary relationships can be derived from the other two, there is
Generate QR Code In C#
Using Barcode generation for .NET framework Control to generate, create QR image in .NET applications.
QR Code Creation In .NET Framework
Using Barcode drawer for ASP.NET Control to generate, create QR Code image in ASP.NET applications.
from the other two relationships For example, suppose that textbook T l is used in two offerings, 0 1 and 0 2 and by two students, SI and S2 K n o w i n g these two facts, y o u do not know the relationship between students and offerings For example, SI could be en rolled in 0 1 or perhaps 0 2 Likewise, the relationship between offerings and textbooks (OfferNo-TextNo) knowing w h o enrolls in an offering and what textbooks a student uses However, the relationship between students and textbooks (StdSSN-TextNo) can be derived by the other two relationships For example, if student SI is enrolled in offering 0 1 and offering 0 1 uses textbook T l , then y o u can conclude that student SI uses text book T l in offering 0 1 Because the Student-Offering the relationship instances Because o f this independence, the Enrol! table and the related associative entity type Enroll have redundancy To remove the redundancy, replace the Enroll entity type with two binary relationships (Figure 78) Each binary relationship converts to a table as shown in Tables 77 and 78 The Enroll and Orders tables have n o redundancies For example, to delete a student's enrollment in an offering (say SI in 0 1 ) , only one row must be deleted from Table 77 In contrast, two rows must be deleted from Table 76 and the Offering-Textbook relationships are independent, y o u know the textbooks used by a student without storing cannot be derived A professor's choice for a collection o f textbooks cannot be derived by
QR Code Creation In .NET
Using Barcode creation for VS .NET Control to generate, create QR Code 2d barcode image in VS .NET applications.
QR Code JIS X 0510 Encoder In VB.NET
Using Barcode generation for .NET Control to generate, create QR Code image in VS .NET applications.
Part Four
Barcode Maker In None
Using Barcode generator for Software Control to generate, create bar code image in Software applications.
Code 3 Of 9 Encoder In None
Using Barcode encoder for Software Control to generate, create Code 39 Extended image in Software applications.
Relational Database Design
EAN / UCC - 13 Generation In None
Using Barcode generation for Software Control to generate, create UCC - 12 image in Software applications.
Data Matrix 2d Barcode Encoder In None
Using Barcode generation for Software Control to generate, create DataMatrix image in Software applications.
FIGURE 78 Decomposed Relationships Example
Create Universal Product Code Version A In None
Using Barcode generation for Software Control to generate, create UPC Symbol image in Software applications.
EAN / UCC - 13 Maker In None
Using Barcode generation for Software Control to generate, create EAN-13 Supplement 5 image in Software applications.
Student StdSSN StdName
Encode Monarch In None
Using Barcode drawer for Software Control to generate, create 2 of 7 Code image in Software applications.
GS1 - 13 Maker In Objective-C
Using Barcode generation for iPhone Control to generate, create European Article Number 13 image in iPhone applications.
Textbook TextNo TextTitle
Barcode Scanner In .NET
Using Barcode recognizer for .NET Control to read, scan read, scan image in .NET applications.
Bar Code Maker In .NET Framework
Using Barcode drawer for Reporting Service Control to generate, create barcode image in Reporting Service applications.
Offering Enroll CX OfferNo OffLocation X> Orders
Code39 Creator In None
Using Barcode encoder for Online Control to generate, create USS Code 39 image in Online applications.
Creating GS1 - 12 In VB.NET
Using Barcode creator for VS .NET Control to generate, create UPC Code image in VS .NET applications.
TABLE 77 Sample Rows of the Binary Enroll Table
Making Linear In .NET
Using Barcode drawer for ASP.NET Control to generate, create Linear image in ASP.NET applications.
DataMatrix Recognizer In C#
Using Barcode reader for .NET Control to read, scan read, scan image in .NET applications.
StdSSN S1 S1
OfferNo 01 02
TABLE 78 Sample Rows of the Binary Orders Table
OfferNo 01 01 02 02
TextNo T1 T2 T1 T2
FIGURE 7 9 M-Way and Binary Relationships Example
Enroll Student StdSSN StdName CX Offering OfferNo OffLocation Offer-Purch
Orders" 2
Textbook TextNo TextTitle
Std-Purch
Purchase
-Text-Purch
If the assumptions change slightly, an argument can be made for an associative entity type representing a three-way relationship Suppose that the bookstore wants to record textbook purchases by offering and student to estimate textbook demand Then the relationship between students and textbooks is n o longer independent o f the other two relationships Even though a student is enrolled in an offering and the offering uses a text book, the student may not purchase the textbook (perhaps borrow it) for the offering In this situation, there is no independence and a three-way relationship is needed In addition to the M-N relationships in Figure 78, there should be a n e w associative entity type and three 1-M relationships, as shown in Figure 79 You need the Enroll textbooks The Purchase relationship to record student selections o f offerings and the Orders relationship to record professor selections o f entity type records purchases o f textbooks by students in a course offering However, a purchase cannot be known from the other relationships
7 Normalization of Relational Tables 235
MVD definition the multivalued depen dency (MVD) A -> -> B | C (read A multidetermines B or C) means that A given A value is associated with a collection of B and C values, and B and C are indepen dent given the rela tionships between A and B and A and C
Multivalued Dependencies a n d Fourth Normal Form
In relational database terminology, a relationship that can be derived from other relation ships is known as a multivalued dependency ( M V D ) A n M V D involves three columns as described in the marginal definition Like in the discussion o f relationship independence, the three columns comprise a combined primary key o f an associative table The nonessen tial or derived relationship involves the columns B and C The definition states that the nonessential relationship (involving the columns B and Q can be derived from the rela tionships A-B and A-C The word multivalued means that A can be associated with a collection o f B and C values, not just single values as in a functional dependency M V D s can lead to redundancies because o f independence among columns You can see the redundancy by using a table to depict an M V D as shown in Figure 710 If the two rows above the line exist and the M V D A > - > B \ C is true, then the two rows below the line will exist The two rows below the line will exist because the relationship between B and C can be derived from the relationships A-B and A-C In Figure 710, value A l is associated with two B values ( B l and B 2 ) and two C values (CI and C2) Because o f independence, value A l will be associated with every combination o f its related B and C values The two rows below the line are redundant because they can be derived To apply this concept to the Enroll table, consider the possible M V D OfferNo > > StdSSN | TextNo In the first two rows o f Figure 7 1 1 , offering 0 1 is associated with stu dents SI and S2 and textbooks T l and T2 If the M V D is true, then the two rows below the line will exist The last two rows do not need to be stored if you know the first two rows and the M V D exists M V D s are generalizations o f functional dependencies (FDs) Every F D is an M V D but not every M V D is an FD A n M V D in which a value of A is associated with only one value o f B and one value o f C is also an FD In this section, we are interested only in M V D s that are not also FDs A n M V D that is not an F D is known as a nontrivial M V D
4 N F definition a table is in 4NF if it does not contain any nontrivial MVDs (MVDs that are not also FDs)
Fourth Normal Form (4NF)
Fourth normal form (4NF) prohibits redundancies caused by multivalued dependencies A s an example, the table EnrolUStdSSN OfferNo TextNo) (Table 76) is not in 4 N F if the M V D OfferNo StdSSN \ TextNo exists To eliminate the M V D , split the M-way table Enroll into the binary tables Enroll (Table 77) and Orders (Table 78)
Copyright © OnBarcode.com . All rights reserved.