1. Conceptual data modeling
University of Banja Luka
Faculty of Electrical Engineering
Conceptual data modeling
9/18/2018

2. Content Introduction Data abstraction Data models E-R model
UML class diagram
Comparation of E-R model and UML class diagram
Conclusion
Conceptual data modeling
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3. Introduction
Database design is one of the most important phases of development of database system (i.e. system with a database)
The goal of this phase is to obtain a conceptual database schema
Poorly organized database can be source of a bad application characteristics, and can lead to frequent, large and often expensive application changes
Therefore, a systematic approach and usage of an adequate methodology is a necessity
Such methodology should be close to man and his perception of the real world, and must have concepts that are able to represent man’s perceptions of the real world in the form of a conceptual schema on a high level of abstraction
First phase of database design is a conceptual modeling, a specification of database structure on a high level of abstraction
Conceptual data modeling
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4. Data abstraction
Database systems support three levels of data abstraction (ANSI/SPARC database architecture, ):
Physical level. The physical level describes how the data are actually stored on the physical medium, with the goal to implement more efficient data access.
Logical level. Logical (conceptual) level describes the logical structure of the entire database.
View level. Many users of the database system need to access only a part of the database. The view level of abstraction exists to simplify their interaction with the system.
Conceptual data modeling
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5. Data abstraction Physical level Logical level View 2 View 1 View n
. . .
View level
(local logical level)
(global logical level)
(how the data are actually stored)
Conceptual data modeling
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6. Data models
Data model is a collection of conceptual tools for describing data, data relationships, data semantics, and consistency constraints
Models that use concepts that are close to man are called high level models or conceptual models
The most often used such model is Entity-Relationship (ER) model
Models that describe how data are actually stored on secondary storage devices are called physical data models or low level models
Between conceptual and physical models there is a class of representational (or implementational) data models that use concepts that are close to man, and also represent how the data are organized in database
Conceptual data modeling
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7. E-R model Concept of E-R data model is simple and intuitive
E-R model is based on a perception of a real world that consists of a collection of basic objects, called entities, and of relationships among these objects
E-R model is very useful in mapping the meanings and interactions of real-world enterprises onto a conceptual schema which can be represented by a graphical notation called E-R diagram
Conceptual data modeling
9/18/2018

8. Basic concepts
Entity is a “thing” or “object” in the real world that is distinguishable from all other objects
Every entity has a set of properties which are in E-R model represented by a set of attributes
Relationship is an association among several entities
Most of the relationships are binary
Key is a set of one or more attributes that, taken collectively, allow us to identify uniquely an entity/relationship in the entity set/relationship set
Conceptual data modeling
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9. E-R model symbols entity type / set attribute primary keyЕ
entity type / set A
attribute A
primary key A
multivalued attribute R A
derived attribute
relationship type / set
discriminating attribute of
weak entity type Е
weak entity type / set A R
identifying relationship
type / set R
m .. n Е
cardinality limits
total participation
of entity type
in relationship
role-
name R Е R Е
role indicator R R
1:1 relationship type
1:M relationship type R R
M:1 relationship type
M:M relationship type
Conceptual data modeling
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10. E-R model symbols superclass/subclass relationship type disjoint
(specialization/
generalization)
disjoint
specialization/
generalization
ISA
ISA
disjoint
total
specialization/
generalization
ISA
union
union/category Е1 R1 Е2
aggregation R2 Е3
Conceptual data modeling
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11. Alternative E-R notations
Entities and attributes
Relationships and cardinality mappings E a) b) c)
A1# A2 A3 … Е A1 A2 A3 … Е
A1# A2 A3 … 1 N 1 N 1 N
Elmasri / Navathe notation A1 Е A2
(0,N)
(0,1)
(0,N)
(1,1)
(1,N)
(0,1)
. . . A3
Min / max notation
Batini / Ceri / Navathe
notation
“Crow’s foot” notation
IE / IDEF1X notations.
Oracle notation
Entity type/set E and
attributes A1 (primary key), A2, A3 ….
Notation with arrows
Generalization and specialization C C C d o S1 S2 S3 S1 S2 S2 S1 S2 S3
Elmasri / Navathe notation
Batini / Ceri / Navathe notation
IE (Information Engineering) notation
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12. Example (conceptual schema for University database)
FirstName
LastName
Address Id
BirthDate
PERSON
GPA
Grade
ISA
Title
disjoint
SAddress
Salary
PROFESSOR
STUDENT
TAKES
Semester
Semester
ENROLS
TEACHES
REG.
Address
Type
Phone
FName
COURSE
C_D
DEPARTMENT
BEL.
FACULTY
Duration
DId
ExamDate
CourseNo
ECTS
ECTS
Title
DName OF
EXAM
Room
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13. Example (conceptual schema for University database)
Conceptual data modeling
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14. UML class diagrams
Unified Modeling Language (UML) provides graphical means for visualization, specification, design, and documentation of models of a software systems
UML can be used for business modeling and modeling of other non-software systems too
UML class diagram is a stucture diagram which shows structure of the system by showing classes and the relationships among the classes
Class diagram is the most widely used diagram in modeling object-oriented system
It can be used for conceptual modeling, although standard notation is not adjusted for that purpose
Conceptual data modeling
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15. Basic concepts Main concepts of the class diagrams are:
Classes
Associations
Class is a descriptor which describes a set of objects (entities) that share the same properties, behaviour and relationships with other objects (entities)
Association is a relationship between several classes
Conceptual data modeling
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16. Basic concepts (examples)
association with specified multiplicity
1..* 1
symmetric association
asymmetric association
aggregation
composition
generalization
association with
association class
ternary association
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17. Example (conceptual schema for University database)
Conceptual data modeling
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18. Comparation of E-R model and UML class diagram
Classes are equivalent to the entity types
Association concept is equivalent to the concept of relationship
Standard UML does not have symbols to specify primary key attributes. In literature, often used specification of primary key is stereotype or {PK} constraint.
Standard UML also does not have means to specify other E-R concepts like weak entity types, composite attributes, etc.
Composition can be used to represent composite attributes of the class
Conceptual data modeling
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19. Comparation of E-R model and UML class diagram
Multiplicity of the association’s end specifies not only the cardinality mapping but also the participation cardinality
In n-ary associations, we can not draw a conclusion about partiticipation cardinalities of the classes
E-R concept of aggregation is not supported in UML class diagram
Specialization constraints on class diagrams are modeled using constraints: {disjoint}, {operlapping}, {complete}, and {incomplete}
Conceptual data modeling
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20. Conclusion First phase of database design is a conceptual modeling
The most often used model for conceptual data modeling is E-R model
Due to intense development and increasing use of UML in all stages of software system life cycle, class diagram is often used during the database design phase, although standard notation is not adjusted for that purpose
In practice, standard UML notation can be adjusted for conceptual data modeling by using different profiles
At our faculty, both notations are used, but with increasing use of UML class diagrams in student projects and diploma thesis
Conceptual data modeling
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21. Q&A
Conceptual data modeling
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