Week6SystemModellingfiltered(1).pdf

System Modelling System Modelling This is the process of developing abstract models of the system that is being developed. This approach will involve some form of diagram. Models are used at different points in the development process. System perspectives     An external perspective, wher...

System Modelling System Modelling This is the process of developing abstract models of the system that is being developed. This approach will involve some form of diagram. Models are used at different points in the development process. 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. 30/10/2014 Chapter 5 System Modeling 3 UML diagram types Activity diagrams, which show the activities involved in a process or in data processing .  Use case diagrams, which show the interactions between a system and its environment.  Sequence diagrams, which show interactions between actors and the system and between system components.  Class diagrams, which show the object classes in the system and the associations between these classes.  State diagrams, which show how the system reacts to internal and external events.  30/10/2014 Chapter 5 System Modeling 4 Models Models are used for a number of reasons including:  Facilitating discussion about an existing or proposed system  Documenting an existing system  Producing a detailed description that can be used to generate a system implementation Documenting Existing Systems A number of approaches are available including Business Process Modelling (BPM) Context models can also be used to help with this scenario. Context Models Context models simply show the other systems in the environment, not how the system being developed is used in that environment. Context Model The context model centres around determining what features are in the system being proposed and what features belong to the system’s environment. Context model helps to determine the boundaries. 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 MHC-PMS Use Case Modelling 1 Each use case represents a discrete task  The use case shows the external interactions with the system  Use Case Modelling 2 In its simplest form a Use Case consists of an ellipse with the actors involved in the use case shown as stick figures. Stick figures are used to represent human interaction and other external systems and hardware. Transfer-data use case Use Cases Use cases are usually accompanied by a structured description in a table format. Tabular description of the ‘Transfer data’ use-case Category Comment Actors Medical receptionist, patient records system (PRS) Description A receptionist may transfer data from the MHC-PMS 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(Input) User command issued by medical receptionist Response(Output) Confirmation that PRS has been updated Comments The receptionist must have appropriate security permissions to access the patient information and the PRS. Tabular description of the ‘Transfer data’ use-case - Alternative Category Comment Actors Medical receptionist, patient records system (PRS) Data Patient’s personal information, treatment summary Stimulus(Input) User command issued by medical receptionist Response(Output) Confirmation that PRS has been updated Normal Operation A receptionist may transfer data from the MHC-PMS 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. Exception (Abnormal Flow) Patients hospital number is entered incorrectly causing the transfer to fail. Additional Comments The receptionist must have appropriate security permissions to access the patient information and the PRS. Use cases involving the role ‘Medical Receptionist’ Patient Record System Object Oriented Analysis (OOA), Design (OOD) and Programming Taking an Object Oriented Approach is one of the most popular approaches when carrying out Analysis and Design. This leads directly into an Object Solution where an OO programming language is used. Class Diagrams 1 Class Diagrams are used when an objectoriented system model is developed. During analysis you try and identify system objects. A class therefore is a generalisation of a system object. Class Diagrams 2 So in the MHC-PMS system we can identify patients as objects. The generalisation of this would be the patient class UML notation is used to represent this class Patient Class Diagram Patient Name Address D.O.B Telephone Number Next of Kin Next of Kin Address Next of Kin Telephone Number New() GetName() GetAddress() Etc. Consultant Class Diagrams Class diagrams are also used to record associations between classes. UML classes and association Classes and associations in the MHC-PMS Class Diagrams 3 When associations are shown the class diagram does not show any detail about the class. Detail can be shown in a separate representation. The Consultation class Generalization This is an approach to handle complexity Generalization allows the identification of common features and allows for some form of specialization. A generalization hierarchy A generalization hierarchy with added detail Aggregation Real world objects are often composed of different parts. In UML we call this aggregation and use a special notation to indication that a particular objects is made up of other objects. The aggregation association