barcode for excel 2010 free nouns for entity type names The 1-M style is similar to the representation in a relational in Software

Generate QR Code JIS X 0510 in Software nouns for entity type names The 1-M style is similar to the representation in a relational

nouns for entity type names The 1-M style is similar to the representation in a relational
Printing Denso QR Bar Code In None
Using Barcode generator for Software Control to generate, create QR Code ISO/IEC18004 image in Software applications.
QR Code Recognizer In None
Using Barcode recognizer for Software Control to read, scan read, scan image in Software applications.
s
Making QR In C#.NET
Using Barcode creator for .NET framework Control to generate, create QR Code ISO/IEC18004 image in Visual Studio .NET applications.
Creating QR Code In VS .NET
Using Barcode maker for ASP.NET Control to generate, create QR image in ASP.NET applications.
Understanding Entity Relationship Diagrams 147
Encode QR-Code In .NET Framework
Using Barcode encoder for Visual Studio .NET Control to generate, create QR Code JIS X 0510 image in VS .NET applications.
Denso QR Bar Code Encoder In Visual Basic .NET
Using Barcode encoder for VS .NET Control to generate, create QR Code image in VS .NET applications.
FIGURE 519 Attendance Entity Type Added to the ERD of Figure 518
Creating GTIN - 128 In None
Using Barcode creation for Software Control to generate, create GTIN - 128 image in Software applications.
Generate Data Matrix 2d Barcode In None
Using Barcode generation for Software Control to generate, create ECC200 image in Software applications.
Student StdSSN StdName
Draw Bar Code In None
Using Barcode encoder for Software Control to generate, create barcode image in Software applications.
Code 128C Generation In None
Using Barcode generation for Software Control to generate, create Code 128 Code Set C image in Software applications.
Offering OfferNo OffLocation OffTime
Painting Code 3/9 In None
Using Barcode creator for Software Control to generate, create Code 3/9 image in Software applications.
EAN13 Maker In None
Using Barcode creation for Software Control to generate, create EAN13 image in Software applications.
Registers
Paint Code11 In None
Using Barcode encoder for Software Control to generate, create Code11 image in Software applications.
Draw Code 128C In Objective-C
Using Barcode printer for iPhone Control to generate, create Code 128 Code Set B image in iPhone applications.
Enrollment EnrGrade s RecordedFor
Read Data Matrix ECC200 In VB.NET
Using Barcode scanner for .NET Control to read, scan read, scan image in .NET applications.
Code 128 Code Set B Decoder In Java
Using Barcode reader for Java Control to read, scan read, scan image in Java applications.
Attendance
Encoding Code 3/9 In Objective-C
Using Barcode generation for iPhone Control to generate, create USS Code 39 image in iPhone applications.
UCC - 12 Maker In VS .NET
Using Barcode creator for ASP.NET Control to generate, create EAN / UCC - 14 image in ASP.NET applications.
AttDate Present
Generating GS1 - 12 In VB.NET
Using Barcode generator for VS .NET Control to generate, create GS1 - 12 image in Visual Studio .NET applications.
UCC - 12 Drawer In VS .NET
Using Barcode generation for .NET framework Control to generate, create UPC-A Supplement 2 image in .NET applications.
database diagram If you feel more comfortable with the 1-M style, then use it In terms of the ERD, the M-N and 1-M styles have the same meaning The transformation of an M-N relationship into 1-M relationships is similar to repre senting an M-way relationship using 1 -M relationships Whenever an M-N relationship is represented as an associative entity type and two 1-M relationships, the new entity type is identification dependent on both 1-M relationships, as shown in Figure 518 Similarly, when representing M-way relationships, the associative entity type is identification depen dent on all 1-M relationships as shown in Figures 516 and 517 There is one situation when the 1-M style is preferred to the M-N style When an M-N relationship must be related to other entity types in relationships, you should use the 1-M style For example, assume that in addition to enrollment in a course offering, attendance in each class session should be recorded In this situation, the 1-M style is preferred be cause it is necessary to link an enrollment with attendance records Figure 519 shows the Attendance entity type added to the ERD of Figure 518 Note that an M-N relationship between the Student and Offering entity types would not have allowed another relationship
with Attendance
Figure 519 provides other examples of identification dependencies Attendance is identification dependent on Enrollment in the RecordedFor relationship The primary key of Attendance consists of AttDate along with the primary key of Enrollment Similarly, Enrollment is identification dependent on both Student and Offering The primary key of Enrollment is a combination of StdSSN and OfferNo
Classification in tlie Entity Relationship Model
People classify entities to better understand their environment For example, animals are classified into mammals, reptiles, and other categories to understand the similarities and differences among different species In business, classification is also pervasive Classifi cation can be applied to investments, employees, customers, loans, parts, and so on For example, when applying for a home mortgage, an important distinction is between fixedand adjustable-rate mortgages Within each kind of mortgage, there are many variations distinguished by features such as the repayment period, the prepayment penalties, and the loan amount This section describes ERD notation to support classification You will learn to use gen eralization hierarchies, specify cardinality constraints for generalization hierarchies, and use multiple-level generalization hierarchies for complex classifications
Part Three
Data Modeling
FIGURE 5 2 0 Generalization Hierarchy for Employees
Generalization hierarchy symbol
Employee EmpNo EmpName EmpHireOate Supertype
HourlyEmp EmpRate Subtypes
SalaryEmp EmpSalary
generalization hierarchy a collection of entity types arranged in a hierarchical structure to show similarity in attributes Each subtype or child entity type contains a subset of entities of its supertype or parent entity type inheritance a data modeling feature that supports sharing of attributes between a supertype and a sub type Subtypes inherit attributes from their supertypes
Generalization Hierarchies
Generalization hierarchies allow entity types to be related by the level o f specialization Figure 520 depicts a generalization hierarchy to classify employees as salaried versus hourly Both salaried and hourly employees are specialized kinds o f employees The
Employee entity type is known as the supertype (or parent) The and HourlyEmp are known as the subtypes (or children) Because
entity types
each subtype entity
SalaryEmp is a
supertype entity, the relationship between a subtype and supertype is known as ISA For example, a salaried employee is an employee Because the relationship name (ISA) is always the same, it is not shown on the diagram Inheritance supports sharing between a supertype and its subtypes Because every subtype entity is also a supertype entity, the attributes o f the supertype also apply to all subtypes For example, every entity o f ing date because it is also an entity o f
SalaryEmp has an employee number, name, and hir Employee Inheritance means that the attributes o f a
supertype are automatically part o f its subtypes That is, each subtype inherits the attributes
SalaryEmp entity type are its direct (EmpSalary) and its inherited attributes from Employee (EmpNo, EmpName, EmpHireDate, etc) Inherited attributes are not shown in an ERD Whenever you have a
o f its supertype For example, the attributes o f the attribute subtype, assume that it inherits the attributes from its supertype
Copyright © OnBarcode.com . All rights reserved.