Tutorial 5 From Use Cases to DFDs (CD-Selection Example) GAO Wei, Rm711, ERBII,

Transcription

1 Tutorial 5 From Use Cases to DFDs (CD-Selection Example) GAO Wei, Rm711, ERBII, wgao@se.cuhk.edu.hk Functional Requirements: CD-Selections Requirement Definition 1. Place Requests for CDs 1.1 Customers will access the Internet system to look for CDs of interest. Some customers will search for special CDs or CDs by specific artists, while other customers want to browse for interesting CDs in certain categories (e.g. rock, jazz, classical). 1.2 When the customer has found a CD he or she wants, the customer will check to see which store(s) have the CD in stock. They will use zip code to find stores close to their location. 1.3 Customers can immediately place a hold on any CD in stock at any of the stores and then come into the store and pick it up (see requirement 3 below). 1.4 If the CD is not available in the customer s preferred store, the customer can request that the CD be special ordered to that store for later pickup. The customer will be notified by when the requested CD arrives at requested store; the CD will be placed on hold (which will expire after 7 days). This process will work similarly to the current special order system. 2. CD Marketing 2.1 The Internet system provides an additional opportunity to market CDs to current and new customers. The system will provide a database of marketing materials about selected CDs that will help Web users learn more about them (e.g., music reviews, links to Web sites, artist information, and sample sound clips). When information about a CD that has additional marketing information is displayed, a link will be provided to the additional information. 2.2 Marketing materials will be supplied primarily by vendors and record labels so that we can better promote their CDs. The Marketing Department will determine what marketing materials will be placed in the system and will be responsible for adding, changing and deleting the materials. 3. Process In-store Holds 3.1 When a CD is available in a store, the system will send a hold request to the instore system at the selected store. 3.2 The in-store system will alter the store staff (through an audible alarm and a popup message). 3.3 Staff will print a label for the requested CD(s), pull them from the shelves, attach the label, and place them on the special order shelf. Just like the special orders, the hold items will be held for 7 days. 3.4 Once the hold has been placed on the shelf, the staff will enter a hold confirmation, and the system will do an inventory adjustment to the main inventory database so that no other holds are accepted for the item.

2 Initial Use Cases for CD Selection

3 Final Use Cases for CD Selection

4 Steps in Building DFDs: 1. Build the context diagram; 2. Create DFD fragments for each use case; 3. Organize DFD fragments into level 0 diagram; 4. Decompose level 0 processes into level 1 diagrams as needed; decompose level 1 processes into level 2 diagrams as needed; etc. 5. Validate DFDs with user to ensure completeness and correctness 1. Context Diagram Draw one process representing the entire system (process 0) Find all inputs and outputs listed at the top of the use cases that come from or go to external entities; draw as data flows Draw in external entities as the source or destination of the data flows

5 2. Create DFD Fragments for Each Use Cases Take Requests Fragment: Maintain Marketing Materials Fragment:

6 Process In-Store Hold Fragment: Each use case is converted into one DFD fragment Number the process the same as the use case number Change process name into verb phrase Design the processes from the viewpoint of the organization running the system Add data flows to show use to data stores as sources and destinations of data Layouts typically place o processes in the center o inputs from the left o outputs to the right o stores beneath the processes

7 3. Integrate the DFD Fragments into Level-0 DFD Combine the set of DFD fragments into one diagram Generally move from top to bottom, left to right Minimize crossed lines Iterate as needed DFDs are often drawn many times before being finished, even with very experienced systems analysts

8 4. Decompose Processes in Level-0 DFD into Level-1 DFD Processes Let s use process 1, Take Requests, for example. First, rethink the use case:

9 Draw Level-1 DFD for CD Selection process 1, Take Requests: Each use case is turned into its own DFD Take the steps listed on the use case and depict each as a process on the level 1 DFD Inputs and outputs listed on use case become data flows on DFD Include sources and destinations of data flows to processes and stores within the DFD May also include external entities for clarity Input data flows shown on a parent DFD are often unbundled on the child diagram using splits Output data flows shown on a child DFD are often bundled using joins and shown as a larger data flow on the parent diagram Stop decomposing DFD: a DFD has at least 3 processes and no more than 7-9.