IS 421 Information Systems Analysis James Nowotarski 28 October 2002

IS 421Information Systems Analysis

James Nowotarski

28 October 2002

• Practice data flow diagramming• Understand requirements for assignment 4 and

quiz 3

Today’s Objectives

Course Map

Contents

1. Introduction

Planning Phase2. Project Initiation3. Project Management

Analysis Phase4. Systems Analysis5. Gathering Information6. Process Modeling7. Data Modeling

1 2 3 4 6 7 8 9 10 115

Assignments

QuizzesFinal

Week

CoreExamReview

Process Modeling in the Analysis Phase

FromPlanningPhase:

System requestFeasibility analysisWorkplan . . .

DevAnalysisPlan

Examine-As-is

IdentifyImprove-ments

DevelopBasicSystemConcepts

DevelopDataModel

DevelopProcessModel

PrepareProposal

ToDesignPhase:

Deliverables:

Analysis Plan Functional Requirements

Quality Requirements

SystemConcept

Data Model

Process Model

System Proposal

Develop Conceptfor To-Be System

Topic Duration

• Grading System Exercise 60 minutes

*** Break 15 minutes

• DFD 60 minutes

• ATB Homework 45 minutes

• Assignment 4 and Quiz 3 Intro 10 minutes

Today’s agenda

Topic Duration



• DFD 60 minutes



Today’s agenda

Grading System Exercise

Grading System ERD

Student

student_id

student_name

Grade [As]

assign_numstudent_id

grade

Assignment

assign_num

assign_descassign_scoring_key

receivesisrecordedfor

results in

is recorded for

Grading System DFD Context

0

GradingSystem

ProfessorStudent

assignment info

student info

grade report

grade info

completed assignment

Grading System DFD Level 0

GradesD1

Maintainstudentsstudent info

Maintainassignments

7

Producegrade report

grade info

Professor

5

Gradeassignment

D2Assignments

D3Students

assignment info

Student

1

grade info

student info

assignment info

grade report

3

studentinfocompleted

assignment

grade info

assignmentinfo

Problem statement

Al Burns is the professor for the class. He manually creates a spreadsheet with all the student information based on a course roster he gets from Campus Connect. He also creates a list of assignments, a description for each assignment, and a grading key for each one.

Students complete the assignment and give them to Al Burns. Al Burns collects the assignments and gives them to Ms. Grader for grading. Ms. Grader grades the assignments based on a key provided by Al Burns, and assigns a score (grade) from 0 to 5. She then records the scores for the students on the spreadsheet.

Grades are reported back to students via a course web page created from the spreadsheet.

Assignment: Draw a context diagram and level 0 diagram for the Grading System.

DFD Step-by-Step

(1) Al Burns is the professor for the class.

Professor

DFD Step-by-Step

(2) He manually creates a spreadsheet with all the student information based on a course roster he gets from Campus Connect.

Professor

CampusConnect

Courseroster

Can’t show it this way, can’t have a data flow going from external entity to external entity

DFD Step-by-Step

(2) He manually creates a spreadsheet with all the student information based on a course roster he gets from Campus Connect.

Professor

CampusConnect

1

Downloadstudent info

Courseroster

Course roster 2

Maintainstudents

D2 Student

Studentinfo

Student info

DFD Step-by-Step

(3) He also creates a list of assignments, a description for each assignment, and a grading key for each one.

Professor

CampusConnect

1


Courseroster

Course roster 2

Maintainstudents

D2 Student

Studentinfo

Student info

3

Maintainassignments

D1 Assignment

Assignmentinfo

Assignment info

DFD Step-by-Step

(4) Students complete the assignment and give them to Al Burns.

Professor

CampusConnect

1


Courseroster

Course roster 2

Maintainstudents

D2 Student

Studentinfo

Student info

3

Maintainassignments

D1 Assignment

Assignmentinfo

Assignment info

Students 4

Collectassignment

Completedassignment

Compeleted assigments

DFD Step-by-Step

(4) Students complete the assignment and give them to Al Burns.

What about distributing the assignment?

Professor

CampusConnect

1


Courseroster

Course roster 2

Maintainstudents

D2 Student

Studentinfo

Student info

3

Maintainassignments

D1 Assignment

Assignmentinfo

Assignment info

Students 4

Collectassignment

Completedassignment


5

Distributeassignment

Assignment info

Assignment info

DFD Step-by-Step(5) Al Burns collects the assignments and gives them to Ms. Grader for grading.

Professor

CampusConnect

1


Courseroster

Course roster 2

Maintainstudents

D2 Student

Studentinfo

Student info

3

Maintainassignments

D1 Assignment

Assignmentinfo

Assignment info

Students 4

Collectassignment

Completedassignment


5


Assignment info

Assignment info

6

Gradeassignment

Completed assignments

DFD Step-by-Step(6) Ms. Grader grades the assignments based on a key provided by Al Burns, and assigns a

score (grade) from 0 to 5.

Professor

CampusConnect

1


Courseroster

Course roster 2

Maintainstudents

D2 StudentStudent info

Student info

3

Maintainassignments

D1 Assignment

Assignmentinfo

Assignment info

Students 4

Collectassignment

Completedassignment


5


Assignment info

Assignment info

6

Gradeassignment


Assignmentinfo

Student info

DFD Step-by-Step

(7) She then records the scores for the students on the spreadsheet.

Professor

CampusConnect

1


Courseroster

Course roster 2

Maintainstudents


Student info

3

Maintainassignments

D1 Assignment

Assignmentinfo

Assignment info

Students 4

Collectassignment

Completedassignment


5


Assignment info

Assignment info

6

Gradeassignment


Assignmentinfo

Student info

D3Grade

Gradeinfo

DFD Step-by-Step(8) Grades are reported back to students via a course web page created from the spreadsheet.

Professor

CampusConnect

1


Courseroster

Course roster 2

Maintainstudents


Student info

3

Maintainassignments

D1 Assignment

Assignmentinfo

Assignment info

Students 4

Collectassignment

Completedassignment


5


Assignment info

Assignment info

6

Gradeassignment


Assignmentinfo

Student info

D3Grade

Gradeinfo

7

Reportgrade

Gradeinfo

Grade info

Student id

Topic Duration



• DFD 60 minutes



Today’s agenda

Data Flow Diagrams

DFD Elements

Key Definitions

• A process model is a formal way of representing business processes– Illustrates processes/activities and how data

moves among them

• Data flow diagramming is a technique for creating a process model.– The primary output of data flow diagramming

is a data flow diagram (DFD)

Key Definitions

• Logical process models describe processes without suggesting how they are conducted

• Physical models include information about how the processes are implemented

Data vs. Process

• Which is the best starting point for developing a system:– Data model?

– Process model?

Some Rules for External Entities

• External people, organizations, systems and data stores

• Reside outside the system, but interact with system

• Either receive info from system (“sink”) or provide data to the system (“source”)

• Examples: Customers, managers• Not clerks or other staff• No relation to entities that are part of

ERD -- Unfortunate duplication of terminology

ExternalEntities

Some Rules for Data Stores

• Internal to the system• Data at rest• Include in system if the system

processes transform the data– Create, Update, Delete

• Every data store on DFD should correspond to an entity on an ERD

• Must have at least one input data flow (or else they never contain any data)

• Usually have at least one output data flow

• Data can only enter a data store from a process and can only leave a data store to a process

Data StoresD1

Some Rules for Data Flows

• Data in motion– From external entity (“source”)

to system

– From system to external entity (“sink”)

– From internal symbol to internal symbol, but always either start or end at a process

– Not designed to show materials flow, just data

Data Flow

Some Rules for Processes

• Always internal to system• Transforms inputs to outputs• Law of conservation of data:

#1: Data stays at rest unless

moved by a process.

#2: Processes cannot consume or manufacture data– Must have at least 1 input data flow (to avoid miracles)– Must have at least 1 output data flow (to avoid black holes)– Should have sufficient inputs to create outputs (to avoid

gray holes)

0.

Processes

Creating Data Flow Diagrams

Creating DFDs is a highly iterative process of gradual refinement.

General steps:

1. Create Use Cases/textual requirements descriptions

2. Create a Context diagram

3. Create DFD fragments for each use case/requirement

4. Create a Level 0 diagram from fragments

5. Decompose to Level 1,2,…

6. Go to step 1 and revise as necessary

7. Validate DFDs with users.

Creating Use Cases

Step 1. Use Cases

• Use case=Set of activities that the system performs to produce some output result

• “Means to an end” - Use case is a more user-friendly way to start working with users to define process model– Use case info is transformed to DFD later

• Use case is a tool for end users, not programmers

• Creating use cases is an iterative process

Process modeling

Prepare use cases

use case reports

Create DFDs

UsersUsers

data flow diagrams

businessprocess

info

• Easier for users to work with than DFDs

• Info gathered through interviews, JAD, etc.

To Design

Step 1. Use Cases

• Anatomy of a use case (see pp.155, 162):– Name

– Short description

– Triggers (system is at rest until trigger event occurs)• External (e.g., customer calls)• Temporal (e.g., payment is overdue)

– Inputs

– Outputs

– Steps

Step 1. Use Cases

• Use case name becomes a process name on the level 0 DFD

• Major inputs become data flows• Major outputs become data flows• Major steps performed become process

names on the level 1 DFD• Destination corresponds to data store or

external entity

Transforming use case to DFD

Creating Data Flow Diagrams

Steps in Building DFDs

2. Create the context diagram

3. Create DFD fragments for each use case

4. Organize DFD fragments into level 0 diagram

5. Decompose level 0 DFDs as needed

6. Go to step 1 and revise as necessary

7. Validate DFDs with users.

Step 2. Context Diagram

• Shows the context into which the business process fits

• Shows the overall business process as just one process

• Shows all the external entities and the data flows into and out of the system from them

Step 2. Context Diagram

• Draw the overall system as a process.– Number the process 0.

– Label the process as the name of the system.

• Draw and label all external entities.• No data stores, unless external.• Draw data flows for all possible data coming from or

going to external entities– Bundle data flows as you deem necessary

Context Diagram Example

Step 3. Create DFD Fragments

• For each use case, create a DFD fragment. • One process (verb phrase) per fragment• Maintain organization’s viewpoint in naming

processes• Layouts often place:

– Process in the center

– Inputs from the left

– Outputs to the right

– Add data stores beneath the processes

DFD Fragment Example

Step 4. Level 0 Diagram

• Integrate DFD fragments to a Level 0 DFD• There will be one Level 0 diagram,

– Shows all the processes that comprise the overall system

– A decomposition of the process on the context diagram

• Shows how information moves from and to each process

Level 0 Tips

• Generally move from top to bottom, left to right

• Minimize crossed lines• Iterate as needed

– The DFD is often drawn many times before it is finished, even with very experienced systems analysts

• Data stores are not usually included

DFD Example

PatientPatient

Find patient

1

Update patient

3

Add new patient

4

Delete patient

2

New patient information

Changes topatient information

Patientname

D1 Patient Information

Patientinformation

Patientinformation to delete

Patientinfo to be updated

Updatedpatientinformation

Patientinformation

Deletedpatient

Some Data Flow Rules

External entity Process Data store

External entityCustomer

information

Process

Data store N/A

Data moved TO:

Data Moving FROM

A process moves data from place to place in the system. On a data flow diagram, processes may move data between certain symbols (data stores, external entities, and other processes). However, data may not be moved without a process. To help you understand and appreciate this, fill in the empty cells in the following table. The cell entries should either be 1) An example of how data could be moved; 2) N/A to indicate this cannot be done.

In this example, “customer information” may be moved from an external entity to a process (e.g., a customer gives their address and credit card information to a sales agent).

The “N/A” suggests data cannot be moved from a data store directly to an external entity, which is true (you need a process in between them).

Relationship Among DFD levels

Step 5. Level 1 Diagrams

• A major step on the use case is usually a process on the Level 1 DFD

• Level 1 DFD shows all the processes that comprise a single process on the level 0 diagram

• Inputs to step are input data flows to process• Outputs to step are output data flows from process• In general,

# level 1 DFDs = # of processes on level 0 DFD

Key Definition

• Decomposition is the process of modeling the system and its components in increasing levels of detail.– Ideally 3-9 processes per DFD

• Balancing involves insuring that information presented at one level of a DFD is accurately represented in the next level DFD.

Are these in balance?0

GradingSystem

ProfessorStudent

assignment info

student info

grade report

grade info

completed assignment

GradesD1

Maintainstudentsstudent info

Maintainassignments

7

Producegrade report

grade info

Professor

5

Gradeassignment

D2Assignments

D3Students

assignment info

Student

1

grade info

student info

assignment info

grade report

3

studentinfocompleted

assignment

grade info

assignmentinfo

Context

Level 0

Hierarchical Consistency

• Balancing Data Flows– An input (output) data flow on a PARENT

diagram must appear on a CHILD diagram as input (output).

– Conversely, an input (output) data flow on a CHILD diagram must appear on a PARENT diagram as input (output).

– A set of data flows on a child diagram that were split from a data flow on a parent diagram must match the parent data flow's composition.

Data Flow Splits and Joins

• A data flow split shows where a flow is broken into its component parts for use in separate processes

• Data flow splits need not be mutually exclusive nor use all the data from the parent flow

• As we move to lower levels we become more precise about the data flows

• A data flow join shows where components are merged to describe a more comprehensive flow

Alternative Data Flows

• Where a process can produce different data given different conditions

• We show both data flows and use the process description to explain why they are alternatives, e.g. – Process credit card rejections

– Process credit card approvals

• Tip -- alternative data flows often accompany processes with IF statements

Tips for Level 1 and Below

• Sources for inputs and outputs listed at higher level• List source and destination of data flows to processes

and stores within each DFD• Depth of DFD depends on overall system complexity

– Two processes generally don’t need lower level (move to higher level)

– More than seven processes become overly complex and difficult to read

Step 7. Validating the DFD

• Syntax errors

– Assure correct DFD structure• Semantics errors

– Assure accuracy of DFD relative to actual/desired business processes

• User walkthroughs• Role-play processes• Examine lowest level DFDs• Examine names carefully

Summary

• The Data Flow Diagram (DFD) is an essential tool for creating formal descriptions of business processes and data flows.

• Use cases record the input, transformation, and output of business processes.

• Eliciting scenario descriptions and modeling business processes are critically important skills for the systems analyst to master.

Which is best?

CustomerCustomer Changeaddress

1Address change info

D1 Customer InformationAddress change info


1Address change info



1 Address info


Address change info

Scenario: A customer notifies a magazine publisher of a change of address.

“For clarity, it is better practice to draw two separate data flows” (p. 149)

Topic Duration



• DFD 60 minutes



Today’s agenda

ATB Homework

ATB ERD

Is an instance of

Computer Model

model_num

manufacturer_nameprocessor_typememory_amt

Workstation

serial_num

purchase_datemodel_numemployee_id

Describes

Employee

employee_id

employee_namephone_numoffice_num

HasAssignedto

Software

package_id

purchase_datepackage_namepackage_version_numpackage_author

Workstation Software

package_idserial_num

install_date

Incident

incident_num

employee_idbegin_timestampend_timestampproblem_descresolution_descstatus_codeserial_numpackage_id

isinstalled on

isassociated with

containsisinstalled on

results in

pertains to

ATB DFD Context

0

ATB TechSupportSystem

End UserEmployee

Tech SupportPerson (TSP)

Boss

WeeklyIncidentReport

OpenIncidentReport

Incident info

New employee info

Incident report

New model

New workstation

New software

New installation

Topic Duration



• DFD 60 minutes



Today’s agenda

Documents

IS 421 Information Systems Analysis James Nowotarski 28 October 2002