1. Mapping UML to RDB, 14.01.2019 - J.P.Nytun – page 1
Mapping Objects to
Relational Databases
Mapping UML to RDB, J.P.Nytun – page 1

2. Mapping UML to RDB, 14.01.2019 - J.P.Nytun – page 2
Why This Mapping?
Object technology, like Java, is in wide use and relational databases are the preferred approach for storage of persistent information.
The relational paradigm is based on mathematical principles: Set theory. The object paradigm has a quite different basis: Inheritance, encapsulation,….
Mapping UML to RDB, J.P.Nytun – page 2

3. Why This Mapping Continues...
In the object paradigm objects are traversed by following links between objects (a link can be an instance of an ordinary association). In the relational paradigm rows in different tables are connected with foreign keys (joining rows in different tables).
(Mapping from UML class diagrams to tables and then back to class diagrams will lead to loss of information.)
Mapping UML to RDB, J.P.Nytun – page 3

4. UML to Relational Mapping: Class to Table
Class diagram
B is a derived attribute. C
a : Integer
c : Double
/b : Integer
NB! Not all classes are persistent.
Table
Table: C
A: Integer
C: Double
Mapping UML to RDB, J.P.Nytun – page 4

5. UML to Relational Mapping: one-to-one associationsX Y
x_pkey
x_a1
y_pkey
y_a1 1
Total participation
Class diagram
Object diagram X1 Y2 X2 Y3 X3 Y1
x_pkey
Tables: Three different solutions
x_a1
y_pkey
y_a1
Table: XY
Table: X and Y
Table: Y and X
Mapping UML to RDB, J.P.Nytun – page 5

6. UML to Relational Mapping: one-to-many associations
Object diagram X Y
x_pkey
x_a1
y_pkey
y_a1 1 *
Class diagram X1 Y2 X2 Y1 Y3 X3 Y4 X4
Tables: One possible solution
y_pkey
y_a1
x_pkey
x_a1
Table: Y
Table: X
Mapping UML to RDB, J.P.Nytun – page 6

7. UML to Relational Mapping: many-to-many associations
Object diagram X1 Y2 Y3 X2 Y1 X4 Y4 X3 X Y
x_pkey
x_a1
y_pkey
y_a1 *
Class diagram
Tables: One possible solution
y_pkey
y_a1
x_a1
Table: Y
x_pkey
Table: X
Table: XY
Mapping UML to RDB, J.P.Nytun – page 7

8. Mapping UML to RDB, 14.01.2019 - J.P.Nytun – page 8
Example
Type
name 1 1
Unit * *
Search
name
Consist
word * *
description * * * *
sequenceNo : int
Collection
Atom * *
url
Mapping UML to RDB, J.P.Nytun – page 8

9. Mapping UML to RDB, 14.01.2019 - J.P.Nytun – page 9
Mapping to Tables - 1
Unit
typeId
name
Type
unitId
name
description
typeId
Type
name 1 1
Unit * *
Search
searchId
word
Search
name
word
description * * * *
UnitSearch
unitId
searchId
Mapping UML to RDB, J.P.Nytun – page 9

10. Mapping to Tables - 2A unitId name description Unit typeId url
Collection
Atom
Here is only one solution presented
( [2] has four different solutions)
Unit
name
description
Collection
Atom
url
Mapping UML to RDB, J.P.Nytun – page 10

11. Mapping to Tables - 2B
Using the object relational features of Postgres
CREATE TABLE Unit (id INTEGER,
name VARCHAR(150),
description VARCHAR(500),
typeId INTEGER)
CREATE TABLE Atom (url VARCHAR(180)) INHERITS (Unit)
CREATE TABLE Collection() INHERITS (Unit)
Unit
name
description
Collection
Atom
url
Mapping UML to RDB, J.P.Nytun – page 11

12. Mapping UML to RDB, 14.01.2019 - J.P.Nytun – page 12
Mapping to Tables - 3
Unit
{ordered}
name
Consist * *
description
sequenceNo : int
Collection * *
unitId
collectionId
Consist
sequenceNo
Collection
Unit
unitId
unitId
name
description
typeId
Mapping UML to RDB, J.P.Nytun – page 12

13. Mapping UML to RDB, 14.01.2019 - J.P.Nytun – page 13
References
[1]Grady Booch, James Rumbaugh, Ivar Jacobson: The Unified Modeling Language User Guide. Addison-Wesley, 1999
[2]Elmasri, Navathe: Fundamentals of database Systems. Addison-Wesley, 2000
[3]Grady Booch, James Rumbaugh, Ivar Jacobson: The Unified Modeling Language Reference Manual. Addison-Wesley, 1999
Mapping UML to RDB, J.P.Nytun – page 13