Information Modelling

Process Technique- DFDhttp://software.rasekhoon.net/

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Systems Thinking

DFDs are a tool that supports systems thinking.

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 outputinput

input output

output

Feedack andControl Loop

The System's Environment(constantly changing)

AProcess

System Decomposition

DecompositionDecomposition is the act of breaking a system into its component subsystems, processes, and subprocesses. Each level of abstraction reveals more or less detail.

Decomposition Diagrams

A decomposition diagram or hierarchy chart shows the top-down, functional decomposition of a system.

Common Process Errors on DFDs

Illegal Data Flows

Diverging and Converging Data Flows

A diverging data flow is one that splits into multiple data flows. Useful for illustrating data that starts out naturally as

one flow, but needs to be routed to parallel processes. Also useful for illustrating multiple copies of the same

output going to different destinations.

A converging data flow is the merger of multiple data flows into a single packet. Useful for illustrating data from multiple sources that

must come back together for some subsequent processing

Diverging and Converging Data Flows

ExternalAgent

External Agents An external agent defines a person, organization

unit, or other organization that lies outside of the scope of the project but that interacts with the system being studied. External agents define the “boundary” or scope of a

system being modeled. As scope changes, external agents can become

processes, and vice versa. Almost always one of the following:

Office, department, division inside the business but outside the system scope.

An external organization or agency. Another business or another information system. One of your system’s end-users or managers

DataStore

Data Stores A data store is an inventory of data.

Frequently implemented as a file or database. A data store is “data at rest” compared to a data flow

that is “data in motion.” Almost always one of the following:

Persons (or groups of persons)

Places Objects Events

(about which data is captured) Concepts

(about which data is important) Data stores depicted on a DFD store all instances of

data entities (depicted on an ERD)

When to Draw Process Models Strategic systems planning

Enterprise process models illustrate important business functions.

Business process redesign “As is” process models facilitate critical analysis. “To be” process models facilitate improvement.

Systems analysis (primary focus of this course) Model the existing system including its limitations Model the target system’s logical requirements

(meaning processes and data flows needed regardless of how the system will be implemented)

Model candidate technical solutions (physical DFDs only)

Model the target technical solution (physical DFDs only)

CASE for DFDs (Sample Screen) from System

Architect 2001

SoundStage Context DFD

MemberServicesSystem

PotentialMember

ClubMember

MarketingDepartment

Warehouse

AccountsReceivable

PastMember

MemberServices

various Inquiry Reponses

various Sales Reports

variousPromotion Reports

Subscription Offer

Member Order

New Subscription

Promotion

Subscription Renewal

Resubscription Offervarious MemberReports

various Subscription Reports

Subscription ProgramNew Promotion

Revised Packing Order

MemberCreditStatus

SoundStage Functional Decomposition Diagram

OrderSubsystem

PromotionSubsystem

OperationsSubsystem

SubscriptionSubsystem

MemberServicesSystem

ProcessOrder

Transactions

GeneratePromotionReports

ProcessMembershipTransactions

ProcessPromotion

Transactions

GenerateSubscription

Reports

GenerateOrder

Reports

ProcessMarketing

Transactions

ProcessSubscriptionTransactions

ProcessWarehouseTransactions

System DFD

GenerateOrder Analysis

Report

ProcessMember OrderCancelation

ProcessMember Order

Revision

ProcessSubscription

Order

ProcessMember Order

ClubDirectors

TimeWarehouse

Warehouse

Member

Member

Member

Member OrderedProducts

Products

Transactions

Products

Member Orders

Member Orders

Members

Members

Inventory Commitment

Product and Availability

Address

New Member Order

New MemberOrdered Products

MemberOrder

CancelationNotice

UpdatedMember

DeletedMember

Order

Deleted MemberOrdered Products

OrderAnalysisReport

End of Day

Orders

OrderedProducts

Packing Order

Packing Order

Member Order Confirmation

InventoryCommitment

Product andAvailability

Updated Memberfrom Updated Order

UpdatedMemberOrderedProducts

UpdatedMember

Order

Member

New MemberOrderedProducts

RelevantTransactions

InventoryCommitmen

t

Product andAvailability

NewMember

OrderUpdated Member

from Order

Member

SubscriptionOrder

ConfirmationMember OrderConfirmation

RevisedPacking Order

Member OrderCancelation

MemberOrder

ChangeRequest

Subscription Order

Member Order

Joe’s YardJoe’s builders’ suppliers has a shop and a yard. His system is

entirely manual. He has a stock list on the wall of his shop, complete with prices. When a builder wants to buy supplies, he goes into the shop and picks the stock items from the list. He writes his order on a duplicate docket and pays Joe, who stamps the docket as paid. The builder takes the duplicate docket and he goes to the yard and hands it to the yard foreman. The yard foreman gets the ordered items from the yard and gives them to the builder. The builder signs the duplicate docket and leaves one copy with the foreman and takes one copy as a receipt. Every week, Joe looks around the yard to see if any of his stock is running low. He rings up the relevant suppliers and reorders stock. He records the order in his order book, which is kept in the yard. The yard foreman takes delivery of the new stock and checks it against what has been ordered. He pays for it on delivery and staples the receipt into the order book. At the end of every month, Joe goes through all the dockets and the order book and produces a financial report for the shareholders.

Draw a context level DFD and a level-1 DFD for this system.

Joe'sYard

Joe Customer

Supplier

Shareholders

Docket &Payment

Signed docket

Supply needs

Supply invoiceSupply order& payment

financialreport

Level-1 DFD processesJoe’s builders’ suppliers has a shop and a yard. His system is

entirely manual. He has a stock list on the wall of his shop, complete with prices. When a builder wants to buy supplies, he goes into the shop and picks the stock items from the list. He writes his order on a duplicate docket and pays Joe, who stamps the docket as paid. The builder takes the duplicate docket and he goes to the yard and hands it to the yard foreman. The yard foreman gets the ordered items from the yard and gives them to the builder. The builder signs the duplicate docket and leaves one copy with the foreman and takes one copy as a receipt. Every week, Joe looks around the yard to see if any of his stock is running low. He rings up the relevant suppliers and reorders stock. He records the order in his order book, which is kept in the yard. The yard foreman takes delivery of the new stock and checks it against what has been ordered. He pays for it on delivery and staples the receipt into the order book. At the end of every month, Joe goes through all the dockets and the order book and produces a financial report for the shareholders.

Verbs from script Has (passive) Buy supplies Picks stock items Writes order Pays joe Stamps docket Takes docket to yard Hands it to foreman Gets items Gives them to builder

Builder signs docket Takes copy as receipt Looks around yard and

reorders Records order in order

book Foreman takes

delivery – checks Foreman pays supplier Staples receipt to

order book Produces financial

report

Remove passive verbs and queries Passive: has stock list Buy supplies

Picks stock items (views list)

Writes orders Pays joe Stamps docket

Customer then Takes docket to yard Hands it to foreman

Gets items Gives them to builder Builder signs docket Takes copy as receipt

Joe then Looks around yard and

reorders Records order in order

book Foreman

takes delivery – checks Foreman pays supplier Staples receipt to order

book Joe

Produces financial report

Level 1 current physical

Customer

Buysupplies

20

getitems

12

Reordersupplies

21

Restock

22

*

Producefinancialreport

Joe's Office5

Joe

OrderbookM3

DocketM1

Money

stock

Shareholders

Supplier

Foreman

*

Taketo

yard

11Supply needs

financialreport

Docket &Payment

Supply order

Docket

Signed docket

Signed docket

Signed docket

Payment

required stock

required stock

completeddocket copy

completeddocket copy

Supply order

supplies

supplies

Payment Payment

Supplierreceipt

Supplierreceipt

completeddocket copy

buildersignature

Buy SuppliesBuy supplies20 DocketM1

Money

Customer

*

WritesOrder

20.1

*

PaysJoe

20.2*

StampDocket(signatu-

re)

20.3

Docket

Payment

Docket

Payment Docket

Get Itemsget items12

Foreman

stock

*

Give itemsto customer

12.1*

Get buildersignature

12.2

*

Givecopy

as receipt

12.3

Customer

Signed docket

required stock

buildersignature

Signed docket

completeddocket copy completed

docket copy

Reorder suppliesReorder supplies21

OrderbookM3

Joe

*

Reorderfromyard

21.1

*

Recordorder

21.2

Supply order

Supply needs

Supply needs

RestockRestock22

stock

OrderbookM3

Supplier

Money

*

Takedelivery

22.1

*

Paysupplier

22.2

supplies

Payment

Supplierreceipt

Supply order

supplies

Payment

Supply order