Information Modelling
Process Technique- DFDhttp://software.rasekhoon.net/
down1%5C549987.Sybase_PowerDesigner_16.1.0.3637.html
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
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