System Modeling - Software Engineering - Lecture Notes, Study notes of Software Engineering

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SE Fundamentals 3 – System Modeling

Topics covered  Context models  Process models  Interaction models  Structural models  Behavioral models  Model-driven engineering

Existing and planned system models  Models of the existing system can help clarify what the existing system does and can be used as a basis for discussing its strengths and weaknesses. These then can lead to requirements for the new system.  Models of the new system can help explain the proposed system to stakeholders. Engineers use these models to discuss design proposals and to document the system for implementation.  In a model-driven engineering process, it is possible to generate a complete or partial system implementation from the system model.

System perspectives  An external perspective, where you model the context or 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 dynamic behavior of the system and how it responds to events.

Use of graphical models  As a means of facilitating discussion about an existing or proposed system  Incomplete and incorrect models are OK as their role is to support discussion.  As a way of documenting an existing system  Models should be an accurate representation of the system but need not be complete.  As a detailed system description that can be used to generate a system implementation  Models have to be both correct and complete.

Context models  Context models are 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 perspective  Context models simply show the other systems in the environment, not how the system being developed is used in that environment  Process models reveal how the system being developed is used in broader business processes  UML activity diagrams may be used to define business process models

Process model of involuntary detention

Use case modeling  Use cases were developed originally to support requirements elicitation and now are 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, time, or other systems.

Transfer-data use case  A use case in the MHC-PMS

Use cases in the MHC-PMS involving the role ‘Medical Receptionist’

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 or use case instance  The objects and actors involved are listed along the top of the diagram, with a dotted line drawn vertically from these  Interactions between objects are indicated by annotated arrows

Sequence diagram for Transfer Data

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  An object class can be thought of as a general definition of one kind of system object  An association is a link between classes that indicates that there is some relationship between these classes  When you are developing models during the early stages of the software engineering process, objects represent something in the real world, such as a patient, a prescription, doctor, etc.