Adobe Systems
1
Data Modeling,
Entity-Relationship Diagram
PB007 Software Engineering I
Lukáš Daubner
daubner@mail.muni.cz
A picture containing text Description automatically generated
PB007 Software Engineering I — Data Modeling, Entity-Relationship Diagram

Adobe Systems
PB007 Software Engineering I — Data Modeling, Entity-Relationship Diagram
2
Entity-Relationship Diagram
̶Data model
̶
̶Not a part of UML
̶Representing the logical structure of relational database
̶
̶Its main components are:
̶Entities
̶Relations
̶Attributes

Adobe Systems
PB007 Software Engineering I — Data Modeling, Entity-Relationship Diagram
3
Entity-Relationship Diagram
Graphical user interface Description automatically generated

Adobe Systems
PB007 Software Engineering I — Data Modeling, Entity-Relationship Diagram
4
Two Worlds Collide
A picture containing building, street, dark, sitting Description automatically generated

Adobe Systems
PB007 Software Engineering I — Data Modeling, Entity-Relationship Diagram
5
Two Worlds Collide
̶World of Objects – Class Diagram
̶Captures data and operations
̶Classes are connected with different relationships with different semantics
̶Objects have own dynamic lifecycle
̶Manipulation with data through object interaction
̶
̶World of Data – Entity-Relationship Diagram
̶Captures just data
̶Simple relationships
̶Represents tables in relational database
̶Manipulation with data through relational algebra
̶
̶

Adobe Systems
PB007 Software Engineering I — Data Modeling, Entity-Relationship Diagram
6
Object-Relational Mapping
̶Conversion „between the worlds“
̶Persistent class ~ Entity type (table)
̶Object ~ Entity (table row)
̶Class attribute ~ Entity attribute (table column)
̶Association/Aggregation/Composition ~ Relation (connection via foreign keys)
̶Inheritance ~ … (manual work needed, see following slides)
̶
̶Mapping is not always 1:1!
̶Single class can be mapped to multiple tables
̶And vice versa
̶Not all classes are persistent (objects stored in database)
̶

Adobe Systems
PB007 Software Engineering I — Data Modeling, Entity-Relationship Diagram
7
Example
Object-Relational Mapping
Graphical user interface, text, application Description automatically generated

Adobe Systems
PB007 Software Engineering I — Data Modeling, Entity-Relationship Diagram
8
Object-Relational Mapping – Inheritance
̶Each class becomes a table
̶Type attribute differentiates the subclass type
̶One object instance in multiple tables
̶More difficult data access
1:1 Mapping
Graphical user interface, application Description automatically generated

Adobe Systems
PB007 Software Engineering I — Data Modeling, Entity-Relationship Diagram
9
Object-Relational Mapping – Inheritance
̶All attributes in one table
̶Some will have NULL value
̶Breaks the 4.NF
̶Suitable for small number of subclasses and few attributes
̶
Merge to superclass

Adobe Systems
PB007 Software Engineering I — Data Modeling, Entity-Relationship Diagram
10
Object-Relational Mapping – Inheritance
̶Superclass attributes are copied to non-abstract subclass tables
̶Suitable if:
̶Superclass has few attributes
̶Many subclasses
̶Subclasses have many attributes
̶
Propagation to subclasses

Adobe Systems
PB007 Software Engineering I — Data Modeling, Entity-Relationship Diagram
11
Normal Forms
̶Technique for data organization and good database design
̶
̶Elimination of repetitive data
̶
̶Reduction of table complexity
̶
̶Problem prevention
̶E.g., update anomalies

Adobe Systems
PB007 Software Engineering I — Data Modeling, Entity-Relationship Diagram
12
1. Normal Form
Normal Forms
̶Satisfies 0. NF (yes, it actually exists)
̶Each attribute is atomic

Adobe Systems
PB007 Software Engineering I — Data Modeling, Entity-Relationship Diagram
13
2. Normal Form
Normal Forms
̶Satisfies 1. NF
̶
̶No partial dependency
̶Each non-key attribute are fully dependent on candidate keys

Adobe Systems
PB007 Software Engineering I — Data Modeling, Entity-Relationship Diagram
14
3. Normal Form
Normal Forms
̶Satisfies 2. NF
̶
̶No transitive dependency
̶Each non-key attribute is dependent on primary key (and candidate keys) only
̶Non-key attributes are mutually independent

Adobe Systems
PB007 Software Engineering I — Data Modeling, Entity-Relationship Diagram
15
You gotta do what you gotta do
Task for this week
̶Process the feedback
̶
̶Create ERD based on  the class diagram
̶Keep it consistent – you model the same system
̶Decompose M:N relationships using entities
̶Normalize to 3. NF
̶
̶Based on the EDR create separate example violating 3. and 2. NF
̶Example – don‘t need to create whole new diagram
̶Add notes explaining the NF violations