1. Object-oriented and Structured System Models

2. Objectives
To understand the context and the functionality of a system using different notations
To review some structured notations
To review some of the notations used in the Unified Modeling Language (UML)

3. A Bridge

4. System modeling Models are used to communicate with stakeholders.
Different models present the system from different perspectives
External perspective showing the system’s context or environment;
Behavioural perspective showing the behaviour of the system;
Structural perspective showing the system or data architecture.

5. Model types
Data processing model shows how the data is processed at different stages.
Composition model shows how entities are composed of other entities.
Architectural model shows principal sub-systems.
Classification model shows how entities have common characteristics.
Stimulus/response model shows the system’s reaction to events.

6. Data-processing models
Data flow diagrams (DFDs) may be used to model the system’s data processing.
These show the processing steps as data flows through a system.
DFDs are an intrinsic part of many analysis methods.
Simple and intuitive notation that customers can understand.

7. Order processing DFD

8. State machine models Used a lot in UML
State machine models model the behaviour of the system in response to external and internal events/stimuli.
often used for modelling real-time systems.
These show
system states as nodes
events as arcs between nodes
when an event occurs, the system moves from one state to another.
Used a lot in UML

9. The States of a System
state —a set of observable circumstances that characterizes the behavior of a system at a given time
state transition —the movement from one state to another
event —an occurrence that causes the system to exhibit some predictable form of behavior
action —process that occurs as a consequence of making a transition

10. Microwave oven model

11. Semantic data models
Semantic data models describe the logical structure of data processed by the system.
An entity-relation-attribute model sets out
the entities in the system,
the relationships between these entities
and the entity attributes
Widely used in database design. Can readily be implemented using relational databases.
No specific notation provided in the UML but objects and associations can be used (VERY SIMILAR to CLASS HIERARCHY DIAGRAMs)

12. Example: Library semantic model

13. Object models
Object models describe the system in terms of object classes and their associations.
An object class is an abstraction over a set of objects with common attributes and the services (operations) provided by each object.
Various object models may be produced
Simple object models
Inheritance models
Aggregation models
Interaction models.

14. Object Model: Class Diagram
Class name
attributes
operations

15. Class (Relationship) Diagram

16. CRC Modeling Analysis classes have “responsibilities”
Responsibilities are the attributes and operations encapsulated by the class
Analysis classes collaborate with one another
Collaborators are those classes that are required to provide a class with the information needed to complete a responsibility.
In general, a collaboration implies either a request for information or a request for some action.

17. CRC Modeling

18. Inheritance models
Organize the domain object classes into a hierarchy.
Classes at the top of the hierarchy reflect the common features of all classes.
Object classes inherit their attributes and services from one or more super-classes. These may then be specialised as necessary.

19. Library class hierarchy

20. User class hierarchy

21. Multiple inheritance

22. Object aggregation
An aggregation model shows how classes that are collections are composed of other classes.
Aggregation models are similar to the part-of relationship in semantic data models.

23. Object aggregation

24. Object behaviour modelling
A behavioural model
shows the interactions between objects
to produce a behaviour that was specified as a use-case
Collaboration diagrams in UML are used to model interaction between objects
Example: Sequence diagrams

25. Sequence diagrams
These show the sequence of events that take place during some user interaction with a system.
You read them from top to bottom to see the order of the actions that take place.

26. Sequence diagram of ATM withdrawal