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Chapter 5 – System Modeling

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

Existing and planned system models  Models of the existing system are used during requirements engineering. They help clarify what the existing system does and can be used as a basis for discussing its strengths and weaknesses. These then lead to requirements for the new system.  Models of the new system are used during requirements engineering to help explain the proposed requirements to other system 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

System boundaries  System boundaries are established to define what is inside and what is outside the system. ▪ They show other systems that are used or depend on the system being developed.  The position of the system boundary has a profound effect on the system requirements.  Defining a system boundary is a political judgment ▪ There may be pressures to develop system boundaries that increase / decrease the influence or workload of different parts of an organization.

The context of the Mentcare system

Process model of involuntary detention

Notations

Interaction models

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 and dependability.  Use case diagrams and sequence diagrams may be used for interaction modeling.

Transfer-data use case  A use case in the Mentcare system

Tabular description of the ‘Transfer data’ use- case Chapter 5 System Modeling 20 MHC-PMS: Transfer data Actors Medical receptionist, patient records system (PRS) Description A receptionist may transfer data from the Mentcase system to a general patient record database that is maintained by a health authority. The information transferred may either be updated personal information (address, phone number, etc.) or a summary of the patient’s diagnosis and treatment. Data Patient’s personal information, treatment summary Stimulus User command issued by medical receptionist Response Confirmation that PRS has been updated Comments The receptionist must have appropriate security permissions to access the patient information and the PRS. 30/10/