Post on 14-Jan-2015
description
Process Modeling:
Data Flow DiagramSystems Analysis and DesignComp 319
Zhella Anne V. Nisperos
Process modeling is a technique for organizing and documenting the structure and flow of data through a system’s processes, and/or the logic, policies, and procedures to be implemented by a system’s processes.
Data Flow Diagrams
Process Modeling
• Graphically represent the processes that capture, manipulate, store and distribute data between a system and its environment and among system components
• Modeling a system’s process– Utilize information gathered during
requirements determination– Structure of the data is also modeled in addition
to the processes• Deliverables and Outcomes
– Set of coherent, interrelated data flow diagrams
Data Flow Diagrams
Process Modeling
• Deliverables and outcomes (continued)– Context data flow diagram (DFD)
• Scope of system
– DFDs of current system• Enables analysts to understand current system
– DFDs of new logical system• Technology independent• Show data flows, structure and functional requirements of new
system
– Project dictionary and CASE repository
Data Flow Diagrams
Process Modeling
A data flow diagram (DFD) is a tool (and type of process model) that depicts the flow of data through a system and the work or processing performed by that system.
Graphically illustrate movement of data between external entities and the processes and data stores within a system
Data Flow Diagrams
Data Flow Diagram (DFD)
DFDs have become a popular tool for business
process redesign.
Data Flow Diagrams
Data flow diagram will support 4 main activities:• Analysis: DFD is used to determine requirements of users• Design: DFD is used to map out a plan and illustrate solutions to analysts and users while designing a new system• Communication: One of the strength of DFD is its simplicity and ease to understand to analysts and users;• Documents: DFD is used to provide special description of requirements and system design. DFD provide an overview of key functional components of the system but it does not provide any detail on these components. We have to use other tools like database dictionary, process specification to get an idea of which information will be exchanged and how.
Data Flow Diagrams
Data Flow Diagram (DFD)
• Four symbols are used– Two different standard sets can be used
• DeMarco and Yourdan
•Gane and Sarson
Data Flow Diagrams
Data Flow Diagramming Mechanics
Based on Gane and Sarson
Data Flow Diagrams
Data Flow Diagramming Mechanics
• Entity– Depicts the origin and/or destination of the
data– Sometimes referred to as an agent/ source/sink– Drawn as a square symbol– should be named with a noun– Name states what the external agent is– Because they are external, many characteristics
are not of interest to us
Data Flow Diagrams
Data Flow Diagramming Mechanics
Based on Gane and Sarson
• Process– Depicts work or action performed on data so
that they are transformed, stored or distributed– Number of process as well as name are
recorded
Data Flow Diagrams
Data Flow Diagramming Mechanics
Based on Gane and Sarson
• Data Store– Depicts data at rest– May represent data in
• File folder• Computer-based file• Notebook
– They are named with a noun– The name of the store as well as the number are
recorded in between lines
Data Flow Diagrams
Data Flow Diagramming Mechanics
Based on Gane and Sarson
• Data Flow– Depicts data that are in motion and moving as a
unit from one place to another in the system.– Drawn as an arrow– Select a meaningful name to represent the data– It should be described with a noun
Data Flow Diagrams
Data Flow Diagramming Mechanics
Based on Gane and Sarson
• Context Diagram– A data flow diagram (DFD) of the scope of an
organizational system that shows the system boundaries, external entities that interact with the system and the major information flows between the entities and the system
• Level-O Diagram– A data flow diagram (DFD) that represents a system’s
major processes, data flows and data stores at a high level of detail
Data Flow Diagrams
Data Flow Diagramming Definitions
• Basic rules that apply to all DFDs– Inputs to a process are always different than
outputs– Objects always have a unique name
• In order to keep the diagram uncluttered, you can repeat data stores and sources/sinks on a diagram
Data Flow Diagrams
DFD Rules
• Process– No process can have only outputs (a miracle)– No process can have only inputs (black hole)– A process has a verb phrase label
Data Flow Diagrams
DFD Rules
• Data Store– Data cannot be moved directly from one store to
another– Data cannot move directly from an outside
source to a data store– Data cannot move directly from a data store to a
data sink– Data store has a noun phrase label– Give each data store a unique reference
number.
Data Flow Diagrams
DFD Rules
• Entity– Data cannot move directly from a source to a
sink– A source/sink has a noun phrase label– The same entity may be used more than once on
a given DFD to avoid crossing data flow lines.
Data Flow Diagrams
DFD Rules
• Data Flow– A data flow has only one direction of
flow between symbols–A data flow cannot go directly back to
the same process it leaves–A data flow to a data store means update–A data flow from a data store means
retrieve or use–A data flow has a noun phrase label
Data Flow Diagrams
DFD Rules
Data Flow Diagrams
• Completeness– DFD must include all components necessary for
system– Each component must be fully described in the
project dictionary or CASE repository• Consistency
– The extent to which information contained on one level of a set of nested DFDs is also included on other levels
Data Flow Diagrams
Guidelines for Drawing DFDs
• Timing– Time is not represented well on DFDs– Best to draw DFDs as if the system has never
started and will never stop.• Iterative Development
– Analyst should expect to redraw diagram several times before reaching the closest approximation to the system being modeled
Data Flow Diagrams
Guidelines for Drawing DFDs
• Gap Analysis– The process of discovering discrepancies
between two or more sets of data flow diagrams or discrepancies within a single DFD
• Inefficiencies in a system can often be identified through DFDs
Data Flow Diagrams
Guidelines for Drawing DFDs
• Process Modeling• DFDs
– Activities supported by DFDs– Symbols– Rules in Creating– Guidelines for Drawing
Data Flow Diagrams
Summary