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DFD Tutorial

DFD Tutorial. IT323. context diagram . Why context diagram ? To know Who will interact with system. What's the main input and output to/from system What kind of stuff that should appear in context?? the main big process : the system external entities : source and sink. Data flow.

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DFD Tutorial

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  1. DFD Tutorial IT323

  2. context diagram • Why context diagram ? • To know • Who will interact with system. • What's the main input and output to/from system • What kind of stuff that should appear in context?? • the main big process : the system • external entities : source and sink. • Data flow. • stuff that is not allowed to be there? • Date store

  3. Draw context diagram This system blocks sites with bad language. The user will enter search words to the system, the system will submit those search words to a search engine and after receiving the search results and keywords for each search result, the system will classify each search result as blocked or unblocked according to prespecified criteria saved in a file in the system. The system saves these search results in the search results database. The system blocks the sites marked blocked. The system then returns the search results to the user. If the user clicks on one of the URL’s in the search results the system will return a website to the user (if the site is unblocked) or will return a blocked site notification to the user (if the site is blocked). The administrator (manager) can submit a request to delete all search results from the search results database, the system will delete them and notify the administrator (manager). The administrator can send an update request to the system to update the criteria in the criteria file, the system will notify the administrator by an update-done notice.

  4. find out context diagram component • This system blocks sites with bad language. • The user will enter search words to the system, the system will submit those search words to a search engine. • source : user Data flow : search word • sink: search engineData flow : search word • after receiving the search results and keywords for each search result, the system will classify each search result as blocked or unblocked according to pre-specified criteria saved in a file in the system. • source: search engine • Data flow : search results and keywords • The system saves these search results in the search results database. • Nothing • The system blocks the sites marked blocked. • Nothing

  5. find out context diagram component 0 Blocking System Search word User Search word search results and keywords search engine

  6. find out context diagram component • This system blocks sites with bad language. • The system then returns the search results to the user. • Sink : user. • Data flow : search results. • If the user clicks on one of the URL’s in the search results the system will return a website to the user (if the site is unblocked) or will return a blocked site notification to the user (if the site is blocked). • source : user Dataflow : URL • sink : user Dataflow : website, block notification

  7. find out context diagram component Search word search engine User URL 0 Blocking System Search Result Search word Website search results and keywords Block notification

  8. find out context diagram component • This system blocks sites with bad language. • The administrator (manager) can submit a request to delete all search results from the search results database, the system will delete them and notify the administrator (manager). • source : Manager dataflow : request to delete • Sink : Manager dataflow : notification for deletion • The administrator can send an update request to the system to update the criteria in the criteria file, the system will notify the administrator by an update-done notice. • source : Manager dataflow : request to update • Sink : Manager dataflow : notification for updating

  9. find out context diagram component Search word 0 Blocking System URL Delete Request Manager User Update Request Search Result Delete Feedback Website Update Feedback Block notification Search word search results and keywords search engine

  10. find 3 errors (rule violations) • The data store DS1, not DS2, should be represented on the level-1 diagram. • Data flow DF3 should be an outflow on the level-1 diagram, and data flow DF6 should not be on the level-1 diagram. • Process P1.4.2 has no inputs.

  11. Draw decision tree • A Fast Food restaurant determined how they reorder food and other items as following: • If an item is perishable, such as meat, vegetables, the restaurant have a standing order with a local supplier stating that a prespecified amount of food is delivered each weekday for that day's use and each Saturday for weekend use. • If the item is not perishable, such as cups, and napkins, an order is placed when the stock on hand reaches a certain predetermined minimum reorder quantity. • The restaurant business depends on season, so standing orders are reduced by specific amounts during the summer and holiday breaks.

  12. Conditions • Type of item: • P = perishable • N = non-perishable • Time of week: • D = weekday • W = weekend • Season of year: • A = academic year • S = summer • H = holiday

  13. decision table

  14. decision tree Standing daily order A 3 S D Standing daily order Summer reduction H 2 W Standing daily order Holiday reduction P 3 A 1 N Standing weekend order S H Standing weekend order Summer reduction Minimum order quantity Standing weekend order Holiday reduction Type of item? Time of week? Season of year?

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