c. Constraints based on user
This is the case where there is no condition applied in order to determine membership in a subclass. Subclass membership is based on database users when they apply the
operation to add an entity to the subclass. No direct representation of this type of constraint in EERD.
d. Constraints based on disjointness aspect
This type of constraint specifies whether an entity can be a member of more than one subclass of the specialization or not.
e. Constraints based on completeness aspect
This type of constraint determines whether an entity has the option for not to belong to any of the subclasses or not.
Since there are various notations to model Disjointness and Completeness constraints, therefore there are many ways can be adopted in order to representdesign
generalization and specialization for these types of constraints.
In context of Chen notation, there are 2 categories of constraints : 1
Disjointness i.
Disjoint : is represented by d symbol
Entity can be a member of at most one of the subclasses ii.
Joint Overlapped : is represented by o symbol.
Entity may be a member of more than one subclass 2
Completeness i.
Total: is represented by double line
An entity must be a member of subclass
ii. Partial: is represented by a single line
Allow an entity not to belong to any of the subclass
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Therefore, there are 4 types of combination between both constraints : i.
Disjoint,total ii.
Disjoint,partial iii.
Overlapped,total iv.
Overlapped,partial In context of UML notation there are 3 categories of constraints :
1 Disjointness the meaning is similar with Chen notation
i. Disjoint
ii. Overlapped
2 Completeness
i. Complete: represents the END of hierarchy tree
ii. Incomplete: represents inheritance may be extended
3 Participation the meaning is similar with Chen notation : TotalPartial
i. Mandatory
ii. Optional
Constraints in UML are placed inside the curly brackets { }.Combination between 1 and 2 or 3 and 1 can be selected.
The results of combinations: If 1 and 2:
i. {disjoint, complete}
ii. {disjoint}
iii. {overlapped, complete}
iv. {overlapped}
If 1 and 3 : i.
{mandatory, disjoint} ii.
{mandatory, overlapped} iii.
{optional, disjoint} iv.
{optional, overlapped}
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Comparison between Chen and UML notation to represent specializationgeneralization constraints can be summarized in Table 3-1.
Table 3-1 : Specializationgeneralization constraints
Chen notation UML notation
Constraint type
Disjointness
-Disjoint :
d symbol
-Overlapped :
o symbol Completeness
-Total : Double line
-Partial : Single line
Disjointness
-Disjoint -Overlapped
Completeness
-Complete -Incomplete
Participation
-Mandatory -Optional
Types of specialization
generalization
1 Disjoint, total 2
Disjoint, partial 3
Overlapped, total
4 Overlapped ,
partial If combination is between type 1 and type 2 :
1 {disjoint,complete} 2 {disjoint}
3 {overlapped,complete} 4 {overlapped}
If combination is between type 3 and type 1 : 1 {mandatory, disjoint}
2 {mandatory,overlapped} 3 {optional,disjoint}
4 {optional,overlapped}
Example
Student
Graduate Undergraduate
d
Note : Type of specialization
generalization shown in this figure is disjoint, total
Student
Graduate Undergraduate
{mandatory,disjoint}
Note : Combination used is between constraint
type 3 and 1
3.2 Exercise
Kategori