Data at rest stay at rest until moved by a process

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1.) Data at rest stay at rest until moved by a process. - “Flow Control” 2.) Processes can neither consume nor create data. - All data coming into and out of a process must be accounted for (no black holes!) - Inputs must be sufficient to produce the outputs (no miracle ex nihlo data creation!)
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Level 0 Diagram Student Registrar Professor 1.0 Register Student for Course D1 Student Class Records D2 Student Payments 2.0 Collect Student Fee Payment 3.0 Produce Student Schedule 4.0 Produce Class Roster 5.0 Produce Enrollment Report Payment Information Student Class Record Student Class Record Student Class Record Student Class Record Student Schedule Class Roster Enrollment Report Student Class Request Receipt Payment Current Logical Level 0 Diagram incorrect Student Class Record
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Level 0 Diagram Student Registrar Professor 1.0 Register Student for Course D1 Student Class Records D2 Student Payments 2.0 Collect Student Fee Payment 3.0 Produce Student Schedule 4.0 Produce Class Roster 5.0 Produce Enrollment Report Payment Information Student Class Record Student Class Record Student Class Record Student Class Record Student Schedule Class Roster Enrollment Report Student Class Request Receipt Payment Current Logical Level 0 Diagram corrected Student Class Record Class Order
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Guidelines A data flow bundled together at one level may be decomposed at a lower level (i.e., broken into component parts) On low-level DFDs, new data flows can be added to represent exceptional situations (i.e., error conditions ) Usually a maximum of 7 processes per DFD.
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49 1.0 Get Customer Address Customer Information Customer Address 1.2 Lookup Customer Address 1.1 Get Customer Phone 1.3 Request Customer Address Customer Phone Customer Information (w/o phone #) Valid Phone Customer Address Invalid Phone Number Message
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50
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Class Exercise Design a context level diagram for one of these examples: - Self-serve grocery checkout (e.g., Giant) - EZPass tag reader/billing system - Payroll system - UMBC ID card-based vending machine - Online florist delivery system - Metro / subway card Please label your two drawings with the names of those who actively participated and turn in at the end of class.
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Class Exercise Now start to diagram the Level-0 DFD for the same work processes. Use cases – what “main processes” are needed? Please label your diagram sets with the names of those who actively participated and turn in at the end of class.
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Class Exercise In your teams, continue working on your DFD exercise. Revisit your context diagram and level-0 . Improve. Try some level-1 diagrams. - UMBC ID card-based vending machine - Self-serve grocery checkout (e.g., Giant) - ATM - Inventory management system
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  • Fall '08
  • Koru,G

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