SE_Lec 05_System Modelling and Context Model

SE_Lec 05_System Modelling and Context Model

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  2  System modelingis 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, which is now almost always based on notations in the Unified Modeling Language (UML).  System modelling helps the analyst to understand the functionality of the system and models are used to communicate with customers.
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  3  Models ofthe 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.
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  4  An externalperspective, 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.
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  5  The UnifiedModelling Language is a standard graphical language for modelling object oriented software.  In 1997 the Object Management Group (OMG) started the process of UML standardization  The objective of UML is to assist in software development  It is not a methodology
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  6  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.
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  8  System ContextDiagrams are diagrams used in systems design to represent the more important external actors that interact with the system at hand.  This type of diagram usually pictures the system at the center, with no details of its interior structure, surrounded by all its interacting systems, environment and activities.  The objective of a system context diagram is to focus attention on external factors and events that should be considered in developing a complete set of system requirements and constraints.
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  9  Identify thesystem and its boundaries (the context)  Identify external entities (providers, receivers of system info)  Identify external data flows (input, output)  However, NO DATA STORE !!!  Note: The whole system itself is a process (it receives input and transforms into output)
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  10  Assumption: thereis no revise order option Customer Vending Machine System Send order Submit order
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  11  Assumption: ONLYwithdrawing money (not transfer, checking balance, or other services….) Customer ATM System Complete transaction Or Revise transaction Request transaction
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  13  A studentsends in an application form containing their personal details, and their desired course  The university checks that the course is available.  If the course is available and the student is enrolled in the course, the university confirms the enrolment by sending a confirmation letter that they are registered for the course to the student.  Or if the course is unavailable the student is sent a rejection letter.  What system is being modeled?
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  15  Letters ofcomplaint received from citizens are entered into a complaints master file by the City Clerk’s office. The date, department code, and a complaint description are stored for each letter. Weekly reports are produced from the complaints master file and given to the City Manager. Two weekly reports are produced: a department summary and a detail report of complaint.
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