lesson-21process modeling define systems modeling and differentiate between logical and physical...
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Lesson-21 Process Modeling
• Define systems modeling and differentiate between logical and physical system models.
• Define process modeling and explain its benefits.
• Recognize and understand the basic concepts and constructs of a process model.
• Read and interpret a data flow diagram.
• Explain when to construct process models and where to store them.
• Construct a context diagram to illustrate a system’s interfaces with its work environment.
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Les
son
Map
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Models: Logical and Physical
Logical models show what a system is or does. They are implementation independent; that is, they depict the system independent of any technical implementation.
Physical models show not only what a system is or does, but also how the system is (to be) physically and technically implemented. They are implementation dependent because they reflect technology choices.
A model is a representation of reality. Just as a picture is worth a thousand words, most models are pictorial representations of reality.
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Why Logical System Models
• Logical models remove biases that are the result of the way the system is currently implemented, or the way that any one person thinks the system might be implemented.
• Logical models reduce the risk of missing business requirements because we are too preoccupied with technical results.
• Logical models allow us to communicate with end-users in nontechnical or less technical languages.
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Process Modeling and DFDsProcess 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.
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.
DFDs have become a popular tool for business process redesign.
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Simple Data Flow Diagram
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Differences Between DFDs and Flowcharts
• Processes on DFDs can operate in parallel (at-the-same-time)– Processes on flowcharts execute one at a time
• DFDs show the flow of data through a system– Flowcharts show the flow of control (sequence and transfer of
control)
• Processes on one DFD can have dramatically different timing– Processes on flowcharts are part of a single program with
consistent timing
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Systems Thinking
Systems thinking is the application of formal systems theory and concepts to systems problem solving.
DFDs are a tool that supports systems thinking.
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Process ConceptsA process is work performed on, or in response to, incoming data flows or conditions.
A System is a Process
TheSystem
is aProcess
input output
input
input output
output
Feedack andControl Loop
The System's Environment(constantly changing)
AProcess
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System Decomposition
Decomposition
Decomposition is the act of breaking a system into its component subsystems, processes, and sub processes. Each level of abstraction reveals more or less detail.
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Decomposition Diagrams
A decomposition diagram or hierarchy chart shows the top-down, functional decomposition of a system.
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Types of Logical Processes
• A function is set of related and ongoing activities of a business.
• An event (or transaction) is a logical unit of work that must be completed as a whole (as part of a function).
• An elementary process (or primitive process) is a discrete, detailed activity or task required to respond to an event. Usually, several such tasks must be completed to respond to an event.
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Common Process Errors
on DFDs
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Policies and Decision Tables
A policy is a set of rules that governs some process of the business.
A decision table is a tabular form of presentation that specifies a set of conditions and their corresponding actions (as required to implement a policy).
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A Simple Decision
Table
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• A data flow represents an input of data to a process, or the output of data from a process.– A data flow may also be used to represent the creation, reading,
deletion, or updating of data in a file or database (called a data store).
– A composite data flow is a data flow that consists of other data flows.
• A control flow represents a condition or nondata event that triggers a process.– Used sparingly on DFDs.
Data Flows & Control Flows
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Data Flow Packet Concept
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Composite and Elementary Data Flows
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Data Flows to and from Data Stores
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Illegal Data Flows
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Data Structures
Data flows can be defined by data structures.
A data structure is a specific arrangement of data attributes that defines the organization of data contained in a data flow.
A data attribute is the smallest piece of data that has meaning to the end-users of a business.