Chapter 5 Flashcards
System Modeling
System modeling
System modeling is the process of developing abstract models of a system, with each model presenting a different view or perspective of that system.
System modeling has now come to mean representing a system using some kind of graphical notation
System modelling helps the analyst to understand the functionality of the system and models are used to communicate with customers.
Can also be part of RE:
- They clarify what the existing system does.
- They explain the proposed requirements to other stakeholders.
System perspectives
An external perspective, where you model the environment of the system.
An interaction perspective, where you model the interactions between a system and its environment, or between the components of a system.
A structural perspective, where you model the organization of a system or the structure of the data that is processed by the system.
A behavioral perspective, where you model the behavior of the system and how it responds to events.
UML (Unified Modeling Language) diagram types
▪ Set of symbols/notations that are generally accepted and can be used to model and design the system.
▪ Types:
Activity diagrams, show the activities involved in a process.
Use case diagrams, show the interactions between a system and its environment.
Sequence diagrams, show interactions between actors and the system and between system components.
Class diagrams, show the object classes in the system and the associations between these classes.
State diagrams, show how the system reacts to internal and external events.
Context models
Used to illustrate the operational
context of a system - they show what lies outside the system boundaries.
Social and organizational concerns may affect the decision on where to position system boundaries.
Architectural models show the system and its relationship with other systems.
Process Models
Process models reveal how the system being developed is used in broader business processes.
Interaction models
Modeling user interaction is important as it helps to identify user requirements.
Modeling system-to-system interaction highlights the communication problems that may arise.
Modeling component interaction helps us understand if a proposed system structure is likely to deliver the required system performance.
Use case diagrams and sequence diagrams may be used for interaction modeling.
Use case modeling
Were developed originally to support requirements elicitation and now incorporated into the UML.
Each use case represents a discrete task that involves external interaction with a system.
Actors in a use case may be people or other systems.
Represented diagrammatically to provide an overview of the use case.
Sequence diagrams
Sequence diagrams are part of the UML and are used to model the interactions between the actors and the objects within a system.
A sequence diagram shows the sequence of interactions that take place during a particular use case.
Structural models
Structural models display the organization (architecture) of a system in terms of the components that make up that system and their relationships.
Structural models may be static models.
You create structural models of a system when you are discussing and designing the system architecture.
Class diagrams
Class diagrams are used when developing an object-oriented system model to show the classes in a system and the associations between these classes.
Object class aggregation models
An aggregation model shows how classes that are collections are composed of other classes.
Behavioral models
They show what happens, or what is supposed to happen, when a system responds to a stimulus from its environment.
You can think of these stimuli as being of two types:
▪ Data: Some data arrives that has to be processed by the system.
▪ Events: Some event happens that triggers system processing.
Data-driven modeling
Show the sequence of actions
involved in processing input data and generating an associated output.
Event-driven modeling
Show how a system responds to external and internal events.
State machine models
These model the behavior of the system in response to external and internal events.
