Lab%203%20-%20Use%20Case%20Diagrams%20%26%20Use%20Case%20Narratives

Lab%203%20-%20Use%20Case%20Diagrams%20%26%20Use%20Case%20Narratives

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L AB 3 U SE C ASE D IAGRAMS SE C ASE N ARRATIVES USER REQUIREMENTS The context system modeling we did in Lab 2 can be thought of as the first step in understanding an existing or proposed information system. The next step in understanding an information system is a detailed understanding of what it needs to do. Initially this may be simply a list of desired functions, such as apply for membership, search library inventory, and check out books. But obviously that doesn't provide isn't enough detail to allow someone to write a computer program. In this lab we will take a list of features and process it through several steps to begin to specify detailed user requirements. SCENARIOS AND USE CASES A scenario is a sequence of steps describing an interaction between a user and an information system. Suppose a user is buying a DVD from an e-commerce site. The user places the DVD in a shopping cart. The user then clicks the check-out button. The user enters shipping information and credit card information and then clicks the final order button. The system checks the credit card and, if the credit card is authorized, marks the order for shipment and sends a confirmation e-mail to the user. The above scenario is one possibility for the sequence of steps. There could be other related scenarios. The user's shipping information and credit card information may already be on file, so the steps of filling that information in could be skipped. The credit card might fail to authorize, in which case a different e-mail would be sent to the user. The user might exit the application before actually placing the order and the system may want to delete the order either immediately or after so many days. Despite the differences in the above scenarios, they are all related to the user goal of buying a DVD. A use case is a set of scenarios related to a single user goal. By detailing out the steps of each alternate scenario and how they relate, a use case can be an invaluable tool in documenting the requirements of a system and defining for programmers how the system should operate. In use cases, users are called actors. An actor is anyone or anything that interacts with the system. It can be a human who uses the system, another information system that passes information in or out of the system, a device (such as a thermostat in a heating system), or even a temporal event (such as the end of an accounting cycle). Page 1
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Systems analysts have identified at least five different kinds of actors: Primary Business Actor – Recipient of the something of measurable value produced by the use case Primary Initiating Actor – Actor that initiates or triggers business process (use case) Primary System Actor – System user that directly interfaces the system to process the use case. External Server Actor
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This note was uploaded on 01/30/2012 for the course CNIT 180 taught by Professor Victorbarlow during the Spring '12 term at Purdue University-West Lafayette.

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Lab%203%20-%20Use%20Case%20Diagrams%20%26%20Use%20Case%20Narratives

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