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Lab%202%20-%20Context%20System%20Modeling

Lab%202%20-%20Context%20System%20Modeling - LAB 2 CONTEXT...

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L AB 2 C O N T E X T S Y S T E M M O D E L I N G MODELING THE PROCESSING OF AN INFORMATION SYSTEM In the first lab we examined the Northwind Microsoft Access information system. Northwind was already designed and built for you to use. What would you do if the information system does not exist, or exists in a form that is difficult to use and needs to be upgraded? In most cases you would want to build or revise the information system. However, you can't just jump into programming. That would be like leaving on a trip without knowing where you were going, how far it was, and if you had enough money to get there. WHY MODEL? A model is a really just a picture of reality. For those of us who have built plastic car models, we really just created with plastic and glue a smaller scale picture of the real thing that is driven on the road. While it is not fully functional of course, the model can be used to represent and describe the real vehicle. Car designers do the same thing but work in the opposite direction. Rather that creating a model of something that is already on the road, they create a model to represent something that they would like to build and put on the road. The model helps them to explain to others (like managers) what the car will look like and do. With the model, they can sell the concept of this new car to management and get the support they need to build it. Modeling is an important tool in analyzing and designing information systems. We can either document the current system or model the new system that we would like to build. If the model shows what the system does and how it does it , the model is called a physical model . Physical models thus show how the system is or will be implemented. However, if the model shows only what the system does or is supposed to do , it is called a logical model . Drawing a logical model is useful because it does not bias the designer or the user for or against any particular method of implementing the system and thus allows all methods to be considered. CONTEXT DIAGRAMS One of the first steps of planning an information system is to think through and model the system context. An information system interacts with the world around it. It receives data as input and produces output for users of the system. Having a picture of these activities makes it easier for the information systems professional and the users of the system to communicate the true purpose and nature of the system. A Context Diagram is a popular CNIT 180: Lab2 – Context System Modeling Page 1
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first step in modeling the proposed system. Its goal is to communicate the scope and
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