lecture03_
TRANSCRIPT
1
Reducing ER-Diagrams to Tables
Problem: Consider the entities of Project, General Task and Employee in a project management or job shop organization. Specify the relations with typical attributes to represent these entities and the relationships between them. [MH91]
EMPLOYEE
SSN Bdate
Name
Sex
Address
Salary
COMPANY DATABSE
DEPARTMENT
Number
NameLocation
Works_For
N 1
Manages
StartDate11
Supervision
1 supervisee
supervisor N
Dependents
EMP_DEP
BdateName
Sex
Relationship
N
1
PROJECT
NameNumber Location
Works_On
Hours
CONTROLS
N N
1
M
Dependents
BdateDeName
Sex
Relationship
PROJECT
NamePNo Location
Dependents-Of Works_On
HoursN
M
N
1N
Supervision CONTROLS
Manages
StartDate
COMPANY DATABSE
1 N1 1
Works_For
EMPLOYEE
SSN Bdate
Name
Sex
Address
Salary
N DEPARTMENT
DNo
DNameDLocation
1
1
Tabular Representation of the ER –EER Diagram [EN94]
STEP 1:• For each regular entity type E in the ER schema,
create a relation R that includes all the simple attributes of E.
• Include only the simple component attributes of a composite attribute.
• Choose one of the key attributes of E as primary key for R.
• If the chosen key of E is composite, the set of simple attributes that form it will together from the primary key of R.
Dependents
BdateDeName
Sex
Relationship
PROJECT
NamePNo Location
Dependents-Of Works_On
HoursN
M
N
1N
Supervision CONTROLS
Manages
StartDate
COMPANY DATABSE
1 N1 1
Works_For
EMPLOYEE
SSN Bdate
Name
Sex
Address
Salary
N DEPARTMENT
DNo
DNameDLocation
1
1
2
EMPLOYEE
EMPLOYEE
SSNBdate
Name
Sex
Address
Salary
FName
MI LName
Manila1950/02/0212000FMariaB.Santos02
Makati1960/01/0110000MJuanA.Cruz01
AddressBdateSalarySexLNameMIFNameSSN
Primary key
Dependents
BdateDeName
Sex
Relationship
PROJECT
NamePNo Location
Dependents-Of Works_On
HoursN
M
N
1N
Supervision CONTROLS
Manages
StartDate
COMPANY DATABSE
1 N1 1
Works_For
EMPLOYEE
SSN Bdate
Name
Sex
Address
Salary
N DEPARTMENT
DNo
DNameDLocation
1
1
DEPARTMENT
DNo
NameLocation
NameDNo
Primary Key
Multi-valued attribute
Dependents
BdateDeName
Sex
Relationship
PROJECT
NamePNo Location
Dependents-Of Works_On
HoursN
M
N
1N
Supervision CONTROLS
Manages
StartDate
COMPANY DATABSE
1 N1 1
Works_For
EMPLOYEE
SSN Bdate
Name
Sex
Address
Salary
N DEPARTMENT
DNo
DNameDLocation
1
1
LocationNamePNo
PROJECT
Name
PNo Location
Primary Key
STEP 2:• For each weak entity type W in the ER schema with
owner entity type E, create a relation R and include all simple attributes (or simple components of composite attributes) of W as attributes of R.
• In addition, include as foreign key attributes of R the primary key attributes(s) of the relation(s) that correspond to the owner entity type(s). This handles the identifying relationship type of W.
• The primary key of R is the combination of the primary key(s) of the owner(s) and the partial key of the weak entity type W, if any.
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Dependents
BdateDeName
Sex
Relationship
PROJECT
NamePNo Location
Dependents-Of Works_On
HoursN
M
N
1N
Supervision CONTROLS
Manages
StartDate
COMPANY DATABSE
1 N1 1
Works_For
EMPLOYEE
SSN Bdate
Name
Sex
Address
Salary
N DEPARTMENT
DNo
DNameDLocation
1
1
DEPENDENTS
Son1990/04/04MJun Santos02
Mother1940/03/01FClara Cruz01
RelationshipBdateSexDeNameESSN
Foreign key
Dependents
Bdate
Sex
Relationship
DeName
Primary key
STEP 3:• For each binary 1:1 relationship type R in the
ER schema, identify the relations S and T that correspond to the entity types participating in R.
• Choose one of the relations (let say S) and include as foreign key in S the primary key of T. It is better to choose an entity type with total participation in R in the role of S.
• Include the entire simple attributes (or simple components of composite attributes) of the 1:1 relationship type R as attributes of S.
Dependents
BdateDeName
Sex
Relationship
PROJECT
NamePNo Location
Dependents-Of Works_On
HoursN
M
N
1N
Supervision CONTROLS
Manages
StartDate
COMPANY DATABSE
1 N1 1
Works_For
EMPLOYEE
SSN Bdate
Name
Sex
Address
Salary
N DEPARTMENT
DNo
DNameDLocation
1
1
MANAGES
FinancePersonnelName
0201MGRSSN
1992/06/061990/05/05StartDate
D2D3DNo
Manages
StartDate
1 1DEPARTMENT
DNo
NameLocation
EMPLOYEE
SSN Bdate
Name
Sex
Address
Salary
NameDNo
Primary key
STEP 4:• For each regular (non-weak) binary 1:N
relationship type R, identify the relation S that represents the participating entity type at the N-side of the relationship type.
• Include as foreign key in S the primary key of the relation T that represents the other entity type participating in R*.
• Include any simple attributes (or simple components of composite attributes) of the 1:N relationship type as attributes of S.
*** The reason for this is that each entity instance on the N-side is related to at most one entity instance on the 1-side of the relationship type.
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Dependents
BdateDeName
Sex
Relationship
PROJECT
NamePNo Location
Dependents-Of Works_On
HoursN
M
N
1N
Supervision CONTROLS
Manages
StartDate
COMPANY DATABSE
1 N1 1
Works_For
EMPLOYEE
SSN Bdate
Name
Sex
Address
Salary
N DEPARTMENT
DNo
DNameDLocation
1
1
EMPLOYEE
DEPARTMENT
DNo
DName Location
Works_For
EMPLOYEE
SSN Bdate
Name
Sex
Address
Salary
N 1
Manila
Makati
Address
D21950/02/0212000FMariaB.Santos02
D11960/01/0110000MJuanA.Cruz01
DNoBdateSalarySexLNameMI
FNameSSN
Manila1950/02/0212000FMariaB.Santos02
Makati1960/01/0110000MJuanA.Cruz01
AddressBdateSalarySexLNameMIFNameSSN
Primary key
STEP 5:• For each binary M:N relationship type R,
create a new relation S to represent R. • Include as foreign key attributes in S the
primary keys of the relations that represent the participating entity types; their combination will form the primary key of S.
• Also include any simple attributes of the M:N relationship (or simple components of composite attributes) as attributes of S. Dependents
BdateDeName
Sex
Relationship
PROJECT
NamePNo Location
Dependents-Of Works_On
HoursN
M
N
1N
Supervision CONTROLS
Manages
StartDate
COMPANY DATABSE
1 N1 1
Works_For
EMPLOYEE
SSN Bdate
Name
Sex
Address
Salary
N DEPARTMENT
DNo
DNameDLocation
1
1
WORKS_ON
30P102
20P101HoursPNoESSN
Works_On
Hours
M NEMPLOYEE
SSN Bdate
Name
Sex
Address
Salary
PROJECT
Name
PNo Location
Primary key
STEP 6:• For each multivalued attribute A, create a
new relation R that includes an attribute corresponding to A.
• Include the primary key attribute K (as a foreign key in R) of the relation that represents the entity type or relationship type that has A as an attribute.
• The primary key of R is the combination of A and K. If the multivalued attribute is composite, include its simple components.
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Dependents
BdateDeName
Sex
Relationship
PROJECT
NamePNo Location
Dependents-Of Works_On
HoursN
M
N
1N
Supervision CONTROLS
Manages
StartDate
COMPANY DATABSE
1 N1 1
Works_For
EMPLOYEE
SSN Bdate
Name
Sex
Address
Salary
N DEPARTMENT
DNo
DNameDLocation
1
1
DEPT_LOCATION
Loc2D1Loc1D2Loc3D2
Loc1D1DLocationDNo
DEPARTMENT
DNo
Name DLocation
Primary key
EMPLOYEE(SSN,FName,MI,Lname,Sex, Salary,Bdate, Address, SUPERSSN,DNo)
DEPARTMENT(DNumber,DName,MGRSSN, StartDate)
DEPT_LOCATION(DNo, Location) PROJECT(PNo, PName, Plocation,DNum)WORKS_ON(ESSN,PNo, Hours)DEPENDENT(ESSN, DependentName, Sex,
Bdate, Relationship)
TABLES as RELATIONS STEP 7:• For each n-ary relationship type R, n>2, create a new
relation S to represent R. • Include as foreign key attributes in S the primary keys
of the relations that represent the participating entity types.
• Also, include any simple attributes of the n-ary relationship type (or simple components of composite attributes) as attributes of S.
• The primary key of S is usually a combination of all the foreign keys that reference the relations representing the participating entity types.
• However if the participation is constraint (min, max) of one of the entity types E participating in R has max = 1, then the primary key of S can be the single foreign key attribute that references the relation E’ corresponding to E. This is because in this case, each entity e in E will participate in at most one relationship instance of R and hence can uniquely identify that relationship instance.
SUPPLY
Part2
Part1
PartNo
30
20
Quantity
P1B
P1A
PNoSName
SUPPLY
Quantity
SUPPLIER
SName
PROJECT
PNo
PART
PartNo
Primary key
M M
M