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3.2 DATA & PROCESS MODELLING - Coggle Diagram
3.2 DATA & PROCESS MODELLING
Data & Process Modelling Concepts
Systems analysts use many graphical techniques to describe an information system
A data flow diagram (DFD) uses various symbols to show how the system transforms input data into useful information.
Data Flow Diagram
A data flow diagram (DFD) shows how data moves through an information system but does not show program logic or processing steps( flow of data between process).
Process symbol
Receives input data and produces output that has a different content, form, or both
Contain the business logic, also called business rules
Avoid;
Spontaneous generation = process produces output, but has no input data flow
Black hole = process that has input, but produces no output
Gray hole = process that has at least one input and one output, but the data obviously is insufficient to generate the output
Data store symbol
Represent data that the system stores
The physical characteristics of a data store are unimportant because you are concerned only with a logical model
Creating a set of DFD
Draw the context diagram so that it fits on one page
Use the name of the information system as the process name in the context diagram
Use unique names within each set of symbols
Do not cross lines
Provide a unique name and reference number for each process
Obtain as much user input and feedback as possible
Step 1 : Draw a context diagram
The WAREHOUSE entity has one outgoing data flow, COMPLETED ORDER.
-Step 2: Draw a Diagram 0 DFD
In the previous step, you learned that a context diagram provides the most general view of an information system and contains a single process symbol, which is like a black box.
-Process 0 on the order system’s context diagram is exploded to reveal three processes (FILL ORDER, CREATE INVOICE, and APPLY PAYMENT), one data store (ACCOUNTS RECEIVABLE), two additional data flows (INVOICE DETAIL and PAYMENT DETAIL), and one diverging data flow (INVOICE).
-Step 3: Draw the Lower-Level Diagrams
To create lower-level diagrams, you must use leveling and balancing techniques.
Leveling is the process of drawing a series of increasingly detailed diagrams, until all functional primitives are identified.
Data Dictionary
A data dictionary, or data repository, is a central storehouse of information about the system’s data
Also defines and describes all data elements and meaningful combinations of data elements
Documenting the Data Elements
The following attributes usually are recorded and described
Data element name and label
Alias
Type and length
Default value
Acceptable values - Domain and validity rules
Security
Responsible user(s)
Description and comments
Typical characteristics of a data store are
Data store name or label
Description
Alternate name(s)
Attributes
Volume and frequency
Typical characteristics of a process
Process name or label
Description
Process number
Process description
Data Dictionary Reports
Many valuable reports
An alphabetized list of all data elements by name
A report describing each data element and indicating the user or department that is responsible for data entry, updating, or deletion
Documenting the Records
Process Description
A process description documents the details of a functional primitive, which represents a specific set of processing steps and business logic
3 Process specification
Modular design
Structured English
Decision Table
Modular design
Symbol
A rectangle represents a step or process
A diamond shape represents a condition or decision
Sequence
The completion of steps in sequential order, one after another.
Selection
The completion of one of two or more process steps based on the results of a test or condition.
Iteration
The completion of a process step that is repeated until a specific condition changes.
Process Description
Structure English
Use only the three building blocks of sequence, selection, and iteration
Use indentation for readability
Decision Tables
Shows a logical structure, with all possible combinations of conditions and resulting actions
Table with three condition
Study each combination of conditions and outcomes. When you have rules with three conditions, only one or two of them may control the outcome, and the other conditions simply do not matter.
If you identify conditions that do not affect the outcome, mark them with dashes (-)
3.Now combine and renumber the rules.
Decision tree
A decision tree is a graphical representation of the conditions, actions, and rules found in a decision table.
Decision trees show the logic structure in a horizontal form that resembles a tree with the roots at the left and the branches to the right.
Like flowcharts, decision trees are useful ways to present the system to management.
Logical & Physical Model
While structured analysis tools are used to develop a logical model for a new information system, such tools also can be used to develop physical models of an information system
Sequence of Models
Many systems analysts create a physical model of the current system and then develop a logical model of the current system before tackling a logical model of the new system
Four-Model Approach
Develop a physical model of the current system, a logical model of the current system, a logical model of the new system, and a physical model of the new system
