download barcode for excel 2010 FIGURE 614 ERD with 1-M Relationship in Software

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FIGURE 614 ERD with 1-M Relationship
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CourseNo CrsDesc CrsUnits
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Offering
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OfferNo OffLocation OffTime
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FIGURE 615
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Conversion of Figure 614 (SQL:2003 Syntax)
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CREATE TABLE Course ( CourseNo CrsDesc CrsUnits CHAR(6), VARCHAR(30), SMALLINT,
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CONSTRAINT PKCourse PRIMARY KEY (CourseNo) CREATE TABLE Offering ( OfferNo OffLocation CourseNo OffTime INTEGER, CHAR(20), CHAR(6) TIMESTAMP, NOT NULL,
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CONSTRAINT PKOffering PRIMARY KEY (OfferNo), CONSTRAINT FKCourseNo FOREIGN KEY (CourseNo) REFERENCES Course
6 Developing Data Models for Business Databases to tables Then, Rule 2 is applied to convert the Has (OfferingCourseNo) The Offering entity type is the child entity type in the Has relationship
relationship to a foreign key Offering
table contains the foreign key because the
Next, y o u can apply the M - N relationship rule (Rule 3) to convert the E R D in Fig ure 616 Following this rule leads to the Enrolls_In o f Enrollsjn types To gain practice with the identification dependency rule (Rule 4), you can use it to con vert the E R D in Figure 618 The result o f converting Figure 618 is identical to Figure 617 except that the Enrolls_In table is renamed Enrollment The E R D in Figure 618 requires table in Figure 617 The primary key and Offering entity is a combination o f the primary keys o f the Student
FIGURE 616 M-N Relationship with an Attribute
Student
StdSSN StdName
Enrollsjn I
EnrGrade
FIGURE 61 7
Conversion of Figure 616 (SQL:2003 Syntax)
CREATE TABLE Student ( StdSSN StdName
CHAR(11), VARCHAR(30), )
CONSTRAINT PKStudent PRIMARY KEY (StdSSN) CREATE TABLE Offering ( OfferNo OffLocation OffTime
INTEGER, VARCHAR(30), TIMESTAMP,
CONSTRAINT PKOffering PRIMARY KEY (OfferNo)) CREATE TABLE E n r o l l s j n ( OfferNo INTEGER, StdSSN CHAR(11), EnrGrade DECIMAL(2,1), CONSTRAINT PKEnrollsJn PRIMARY KEY (OfferNo, StdSSN), CONSTRAINT FKOfferNo FOREIGN KEY (OfferNo) REFERENCES Offering, CONSTRAINT FKStdSSN FOREIGN KEY (StdSSN) REFERENCES Student
Part Three
Data Modeling
FIGURE 618 Enrollsjn M-N Relationship Transformed into 1-M Relationships
Student StdSSN StdName
Offering OfferNo OffLocation
Registers -
Enrollment EnrGrade
Grants
FIGURE 619 Examples of 1-M and M-N Self-Referencing Relationships
(a) Manager-subordinate
(b) Course prerequisites
Faculty FacSSN FacName
: Supervises
Course CourseNo CrsDesc CrsUnits
i Prereqjo
>o--
two applications o f the identification dependency rule Each application o f the identifica tion dependency rule adds a component to the primary key o f the Enrollment table You can also apply the rules to convert self-referencing relationships For example, y o u can apply the 1-M and M - N relationship rules to convert the self-referencing relationships in Figure 619 Using the 1-M relationship rule, the Supervises relationship converts to a foreign key in the Faculty table, as shown in Figure 620 U s i n g the M - N relationship rule, the Prereq_To relationship converts to the PrereqJTo table with a combined primary key o f the course number o f the prerequisite course and the course number o f the dependent course You also can apply conversion rules to more complex identification dependencies as depicted in Figure 6 2 1 The first part o f the conversion is identical to the conversion o f Figure 618 Application o f the 1-M rule makes the combination o f StdSSN and OfferNo foreign keys in the Attendance table (Figure 622) Note that the foreign keys in Attendance refer to Enrollment, not to Student and Offering Finally, one application o f the identifica tion dependency rule makes the combination o f StdSSN, OfferNo, and AttDate the primary key o f the Attendance table table The conversion in Figure 622 depicts a situation in which the transformation o f a weak to a strong entity may apply (Section 623) In the conversion, the Attendance tity will eliminate the combined foreign key in the Attendance table contains a combined foreign key (OfferNo, StdSSN) Changing Enrollment into a strong en
6 Developing Data Models for Business Databases
FIGURE 620
Conversion of Figure 619 (SQL:2003 Syntax) CHAR(11), VARCHAR(30), CHAR(11),
CREATE TABLE Faculty ( FacSSN FacName FacSupervisor
CONSTRAINT PKFaculty PRIMARY KEY (FacSSN), CONSTRAINT FKSupervisor FOREIGN KEY (FacSupervisor) REFERENCES Faculty CREATE TABLE Course ( Courseno CHAR(6), CrsDesc VARCHAR(30), CrsUnits SMALLINT, CONSTRAINT PKCourse PRIMARY KEY (CourseNo)
CREATE TABLE Prereq_To ( PrereqCNo CHAR(6), DependCNo CHAR(6), CONSTRAINT PKPrereq_To PRIMARY KEY (PrereqCNo, DependCNo), CONSTRAINT FKPrereqCNo FOREIGN KEY (PrereqCNo) REFERENCES Course, CONSTRAINT FKDependCNo FOREIGN KEY (DependCNo) REFERENCES Course
FIGURE 621 ERD with Two Weak Entity Types
Student StdSSN StdName
Offering OfferNo OffLocation OffTime
Registers
Enrollment EnrGrade
X D Grants -H
Attendance AttDate Present
Recorded
FIGURE 622
Conversion of the Attendance Entity Type in Figure 621 (SQL:2003 Syntax)
CREATE TABLE Attendance ( OfferNo INTEGER, StdSSN CHAR(11), AttDate DATE, Present BOOLEAN, CONSTRAINT PKAttendance PRIMARY KEY (OfferNo, StdSSN, AttDate), CONSTRAINT FKOfferNoStdSSN FOREIGN KEY (OfferNo, StdSSN) REFERENCES Enrollment )
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