Data and Process Modeling

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Data and process modeling Chapter 5

Introduction 

You use data and process modeling techniques to develop a logical model of the proposed system and document the system requirements 



Logical model shows what the system must do Physical model describes how the system will be constructed

Introduction 

Three main tools:   

Data Flow Diagrams (DFD) Data dictionary Process description

Overview of Data and Process Modeling Tools

Data Flow Diagrams (DFD) 



It uses various symbols to show how the system transforms input data into useful information A set of DFDs provides a logical model that shows what the system does, not how it does it.

1. 2. 3. 4.

DFDs Symbols

Process Symbol Data Flow Symbol Data Store Symbol Entity Symbol

Process Symbol 

Process 

 

Receives input data and produces output that has a different content, form, or both. Can be very simple or quite complex Contain the business logic, also called business rules, that transform the data and produce the required results.

Process Symbol 

Also referred to as a black box

DATA FLOW SYMBOL



Data Flow 



A path for data to move from one part of the information system to another. Represents one or more data items.

DATA FLOW SYMBOL POLICY NUMBER

HOURS WORKED

DATE OF BIRTH

APPLY INSURANCE PREMIUM

CALCULATE GROSS PAY

CALCULATE GROSS PAY

PAYMENT AMOUNT



Spontaneous Generation



Black Hole



Gray Hole

PAY RATE

FINAL GRADE

DATA STORE SYMBOL 

Data Store 



Used to represent data that the system stores because one or more processes need to use the data at a later time. The physical characteristics of a data store are unimportant because you are only concerned with a logical model.

CORRECT

POST PAYMENT

CREATE INVOICE

CUSTOMER PAYMENT

INVOICE

CUSTOMER PAYMENTS

ACCOUNTS RECEIVABLE

DAILY PAYMENTS

INVOICE DETAIL PAYMENT DETAIL

SYMPTOM

ADMIT PATIENT

ADMISSION FORM

PREPARE DEPOSIT

POST PAYMENT

DIAGNOSE PATIENT

PATIENTS TREATMENT TREAT PATIENT

INCORRECT

COURSES

DAILY PAYMENTS

STUDENTS

POST PAYMENT

CUSTOMER PAYMENT

DAILY PAYMENT

BOOK FLIGHT

FLIGHT REQUEST

PASSENGERS

ENTITY SYMBOL  



Symbol for the entity A DFD shows only external entities that provide data to the system or receive output from the system A DFD shows the boundaries of the system and how the system interfaces with the outside world.

ENTITY SYMBOL  

Also called TERMINATORS SOURCE 



An entity that supplies data to the system

SINK 

An entity that receives data from the system

CORRECT

BANK

CUSTOMER

ORDER

BANK DEPOSIT

PAYMENT

PAYMENT

CUSTOMER

INVOICE

VERIFY ORDER

PREPARE DEPOSIT

APPLY PAYMENT

APPLY PAYMENT

CUSTOMER

PAYMENT

APPLY PAYMENT

INCORRECT

PAYROLL DEPARTMENT

PAYCHECK

EMPLOYEE

CUSTOMER

PAYMENT

ACCOUNTS RECEIVABLE

BANK

BANK DEPOSIT

DAILY PAYMENTS

CREATING A SET OF DFDs 



Create a graphical model of the information system based on your fact-finding results Performing three main tasks   

Step 1: Draw a context diagram Step 2: Draw a diagram 0 DFD Step 3: Draw the lower-level diagrams

GUIDELINES FOR DRAWING DFDs  

  



Draw the context diagram so 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 nor 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 

Context Diagram 

A top-level view of an information system that shows the system’s boundaries and scope.

Step 2: Draw a Diagram 0 DFD 



To show detail inside the black box, you create DFD diagram 0. Diagram 0 



 

It zooms in on the system and shows major internal processes, data flows, and data stores. It repeats the entities and data flows that appear in the context diagram. It must retain all the connections that flow into and out of process 0. It provides an overview of all the components that interact to form the overall system.

2

STUDENT RECORDS SYSTEM

ASSIGN FINAL GRADE

FINAL GRADE

GRADING DETAILS

CLASS ROSTER 1

3

STUDENT GRADE

GRADE STUDENT WORK GRADING PARAMETERS

CLASS ROSTER

CLASS GRADEBOOK

D1

ESTABLISH GRADEBOOK

GRADEBOOK

CLASS DETAILS

GRADING PARAMETERS

4 INSTRUCTORS

GRADE REPORT

PRODUCE GRADE REPORT

STUDENTS



Diverging Data Flow 



Parent Diagram 



The higher-level diagram

Child Diagram 



A data flow in which the same data travels to two or more different location.

The lower-level diagram

Function Primitive 

A process that consists of a single function that is not exploded further

Step 3: Draw the Lower-level Diagram 



To create a lower-level diagram, you must use leveling and balancing. Leveling 





The process of drawing a series of increasingly detailed diagrams, until all functional primitives are identified. Also called Exploding, Partitioning, or decomposing.

Balancing 

Maintains consistency among a set of DFDs by ensuring that input and output data flows align properly.

Data Dictionary 









Also known as Data repository, is a central storehouse of information about the system's data. Used to collect, document, and organize specific facts about the system, including the contents of data flows, data stores, entities, and process. Defines and describes all data elements and meaningful combinations of data elements. Data Elements 

Also known as Data item or Field



The smallest piece of data that has meaning within an information system.

Records 

Also known as Data structure



A meaningful combination of related data elements that included in a data flow or retained in a data store.

Data Dictionary Reports 



Serves as a central storehouse of documentation for an information system. You can obtain the following:  





An alphabetized list of all data elements by name A report describing each data elements and indicating the user or department that is responsible for data entry, updating, or deletion A report of all data flows and data stores that use a particular data element Detailed reports showing all characters of data elements, records, data flows, processes, or any other selected item stored in the data dictionary.

Process Description Tools 



Documents the details of a functional primitives, and represents a specific set of processing steps and business logic. Using a set of Process Description Tools, you create a model that is accurate, complete, and concise.

Process Description Tools 

Modular Design 





Combination of three logical structures, sometimes called control structures, which serves as building blocks for the process. Each logical structure must have a single entry and exit point. Three structures (can all be combined to in various ways

Process

Conditio n or Decision

to describe process logic)   

Sequence Selection Iteration

Logic

Structure of Modular Design 

Sequence 

Completion of steps in sequential order, one after another.



One or more of the steps might represent a sub process that contains additional logical structure

Verify Product Code

Verify Price

Verify Stock Level

Structure of Modular Design 

Selection 

The process of one of two or more process steps based on the results of a test or condition.

Hour s >40? No

Yes

Calculate Overtime Pay

Structure of Modular Design 

Iteration 

Also known as Looping



The completion of a process step that is repeated until a specific condition changes.

End of File Yes

No Print Paycheck

Process Description Tools 

Structured English 

A subset of standard English that describes logical processes clearly and accurately



Must conform to the following rules 

Use only the three building blocks of sequence, selection, and iteration



Use indentation for readability



Use a limited vocabulary, including standard terms used in the data dictionary and specific words that describe the processing rules

Process Description Tools 

Structured English 

Might look familiar to programming students because it resembles pseudocode

Process Description Tools 

Decision Tables 

Shows a logical structure, with all possible combinations of conditions and resulting actions



It is important to consider every possible outcome to ensure that you have overlooked nothing

Process Description Tools 

Decision Tables 

Can have more than two possible outcomes



Often are the best way to describe a complex set of conditions

Process Description Tools 

Decision Trees 

Graphical representation of the conditions, actions, and rules found in a decision table



Whether to use a decision table or tree often is a matter of personal preference

Logical Versus Physical Models 



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 A physical model shows how the system’s requirements are implemented

Logical Versus Physical Models 

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 Performing that extra step allows them to understand the current system better

Logical Versus Physical Models 

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 The only disadvantage of the four-model approach is the added time and cost

Chapter Summary 





During data and process modeling, a systems analyst develops graphical models to show how the system transforms data into useful information The end product of data and process modeling is a logical model that will support business operations and meet user needs Data and process modeling involves three main tools: data flow diagrams, a data dictionary, and process descriptions

Chapter Summary 

 



Data flow diagrams (DFDs) graphically show the movement and transformation of data in the information system DFDs use four symbols A set of DFDs is like a pyramid with the context diagram at the top The data dictionary is the central documentation tool for structured analysis

Chapter Summary



Each functional primitive process is documented using structured English, decision tables, and decision trees Structured analysis tools can be used to develop a logical model during one systems analysis phase, and a physical model during the systems design phase



Chapter 4 Complete



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