Flow oriented modeling

Flow oriented modeling

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  Flow-Oriented Modeling Represents howdata objects are transformed at they move through the system A data flow diagram (DFD) is the diagrammatic form that is used Considered by many to be an ‘old school’ approach, flow- oriented modeling continues to provide a view of the system that is unique—it should be used to supplement other analysis model elements 1
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  The Flow Model Everycomputer-based system is an information transform .... computer input based output system 2
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  Flow Modeling Notation external entity process data flow data store 3
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  External Entity Aproducer or consumer of data Examples: a person, a device, a sensor Another example: computer-based system Data must always originate somewhere and must always be sent to something 4
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  Process Adata transformer (changes input to output) Examples: compute taxes, determine area, format report, display graph Data must always be processed in some way to achieve system function 5
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  Data Flow Data flowsthrough a system, beginning as input and be transformed into output. base compute area triangle height area 6
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  Data Stores Data is often stored for later use. sensor # sensor #, type, look-up location, age sensor report required data type, location, age sensor number sensor data 7
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  Data Flow Diagramming Guidelines • All icons must be labeled with meaningful names • The DFD evolves through a number of levels of detail • Always begin with a context level diagram (also called level 0) • Always show external entities at level 0 and 1 8
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  • The level0 data flow diagram should depict the software/system as a single bubble • Primary input and output should be carefully noted • Refinement should begin by isolating candidate processes, data objects, and data stores to be represented at the next level • All arrows and bubbles should be labeled with meaningful names • Information flow continuity must be maintained from level to level • One bubble at a time should be refined 9
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  Constructing a DFD– level 0 • Review the data model to isolate data objects and use a grammatical parse to determine “operations” • Determine external entities (producers and consumers of data) • Create a level 0 DFD 10
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  Constructing a DFD– level 1 • A “grammatical parse” on the narrative that describes the context level bubble. • Isolate all nouns (and noun phrases) and verbs (and verb phrases). • Verbs are processes which are represented as bubbles in a subsequent DFD. • Nouns are external entities / data objects / control objects / data store. 13
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  Constructing a DFD– level 2 • Refines the monitor sensors process 15
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  PSPEC • The process transform performs password validation at the control panel for the SafeHome security function. • Process password receives a four-digit password from the interact with user function. • The password is first compared to the master password stored within the system. • If the master password matches , [valid id message = true] is passed to the message and status display function. • If the master password does not match , the four digits are compared to a table of secondary passwords (they may be assigned to house guests and/or workers who require entry to the home when the owner is not present). • If the password matches an entry with the table, [valid id message = true] is passed to the message and status display function. • If there is no match, [valid id message = false] is passed to the message and status display function. 17