Download Structuring System Requirements

Structuring System
Requirements
IS 582
Dr. Dania Bilal
Spring 2006
Recap of Systems Analysis Phase
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Determining user requirements
Structuring user requirements
Selecting the best system design strategy
Structuring System Requirements
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Data Flow Diagrams (DFDs)
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Analysis tool to structure user requirements in a
system
Graphically represents data movement or flow in
an information system and relationships among
data flow
DFDs
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Show the processes that transform or change
data
Focus on movement of data between
processes
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DFDs are called process models
Process modeling shows data flow through the
system based on an organization’s rules, decisions,
and policies
DFDs
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Increase software development productivity
by
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avoiding mistakes in representing user requirements
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Saving money in software cost
Based on user requirements gathered during
planning stage
Evolve from the more general to the more
specific
DFDs
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DFDs of current system
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Used to understand current system
DFDs of new logical system
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Used to show data flow, structure, and functional
requirements of new system
DFDs Symbols
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Flow of data is represented by
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Data flow
Data Store
Process
Source (external entities)
DFDs Symbols
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Data Flow
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Data in motion from one place in a system to
another
Example: user query in a database
DFDs Symbols
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Data store
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Physical location or various locations of data in
an information system
Example: a data store in a circulation system
contains data about students, faculty, staff,
community users, etc.
DFDs Symbols
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Process
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Actions performed on data for transformation,
storage, and distribution
May represent data in
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File folder, computer-based file, notebook
DFDs Symbols
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Source/sink
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Depicts the origin and/or destination of data
Refers to a external entity
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Another organization or unit that sends and receives
information from the system
A person who interacts with the system, inside or outside
Another information system that exchanges information with
the system under analysis
DFDs Symbols
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Source/sink
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Defines the system boundaries
Data originates outside a system from one or
more sources, and the system produces
information to one or more sinks
DFD Mechanics
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How the four symbols are represented?
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Data flow: drawn as an arrow
Data store: drawn as a rectangular
Process: drawn as a circle
Source/sink: drawn as a square
DFD Definitions
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Level-0 diagram
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Context diagram

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Represents a system’s major processes, data flow,
and data stores at the highest level of detail
Shows major flow between entities and the
system (too general)
Level-N diagram
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A DFD that results from a decomposed Level-0
diagram
Types of DFDs
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Current logical
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Depicts current system
New logical
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Has additional functions
Inefficient data flows are reorganized
DFDs
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New physical
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Depicts physical implementation of the new
system
Examples
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Visit
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http://www.umsl.edu/~sauter/analysis/dfd/dfd.htm
Class Activity
Do a DFD for an automation function and its
tasks. Since we don’t have Visio or the like
software, use PPT.
(You will work on this as time permits).
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