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DATA FLOW DIAGRAMS (DFD):
Sources and Sinks:– Define System Boundaries
Process (transformation)– transforms data - no detail of how the transformation is done– Inputs and Outputs– Manual / Automated– Process #, Brief descriptive label (action verb and object
clause)
Label
(External
Entities)
1.Receive Orders
1Order Clerk:Order Entry
#Desc.Who
Data Store:
– only processes can connect to data stores– A store is passive, process initiates flows
Data Flow:
# InvoicesInvoices
Identifiers (letters,etc)
Name
Customer
Customer
Warehouse
1.Receive Order
2.Ship goods
3.Collect Pmts
Invoices
Orders
Customers
Pmt. Inquiries
Invoice Statement
Cust.Name,Address
Cust.Name,Address
Cust.Name,Address
Shipping DetailGoods info
Goods info
Invoice Details
OrdersInvalid Orders
Billing Info
DFD Example
Order Detail
Data Store:• may be a fundamental user requirement or an
implementation store placed there for convenience.
Enter Order Process Order(Essential Model)
Validated Order
Acknowledgement
Order Detail
Enter Order Process OrderOrders
Acknowledgement
Order Detail
xx yy
(Implementation Model)
Update/Create
Use/Retrieval
Naming data Flows:
Enter orderOrders
Orders? What transformation
For Essential model name should be implementation free
e.g. Course Request Form vs. Form23
Employee
Create newmember account
1.
Freeze accountnumber
2.
Generateemployeebank stat.
3.
AccountsReceivable
Dept
Employee fileMember Accts.
Modified accountstatus
Employeestatus
Employee IDand address
Frozen acct. notification
Existingaccount
Membershipapplication
Bank statement
Common DFD Errors
• Common DFD Errors:
– Process1 has inputs but produces no outputs. This is called a black hole
– Process 2 produces outputs but receives no inputs. This is called a miracle
– Process 3 has inputs and outputs ; however the inputs are not sufficient to produce the outputs. This is called a gray hole.
DS1 DS Name
E-1
2.0P-2
E-2
1.0P-1
DF-2
DF-3
DF-5
DF-4DF-6
DF-2
DF-1
DFD Errors
Pay Phone
Bill
Phone Company
Itemized Calls
Statement and Invoice
Correct Use of Packet Concept
Itemized Calls
Statement
Invoice
The Data Flow Packet Concept
Authorize Payment by Bank
Card
Customer
Credit Vouchers Due
Payments
Credit Receipt
Authorize Payment by Bank
Card
Customer
Credit Vouchers Due
Payments
Customer Receipt
Approved Credit Voucher
Sale
Diverging data flows are implementation oriented and should be avoided on essential DFDs
Diverging Data Flows
The Explosion Approach to drawing DFDs:As suggested by DeMarco and others, this diagramming technique requires the analyst to draw multiple DFDs, each one exploding from a single process on another diagram, until the system is completely modeled
mThe
System
1.2
1.
pn
3.
2.
1.3
1.1.3.1 3.2
ZZZ
XXX
A
H
G
Z
DE
C M
L
KA
B
B
A C
BD
Z
Overview DFD
Context DFD
1.0
1.4 2.3
2.22.1
1.4.1
1.4.41.4.3
1.4.2
1.3
1.1 1.2
3.02.0
Explodes to
Explodes toExplodes to
Level 2 Diagram 1.4
Level 1 Diagram 1
Level 1 Diagram 2
Grandchild
Child Child
ParentFunctional Decomposition and Leveled DFDs
id
TOP - DOWN analysis & functional decomposition
1.function
A
0The System
1.1Activity 1 of function A
Task 1.1.1
Task 1.1.2
Task 1.1.3
1.2Activity 2 of function A
Task 1.2.1
Task 1.2.2
2.1Activity 1 of function B
Task 2.1.1
Task 2.1.2
2.2Activity 2 of function B
Task 2.2.1
Task 2.2.2
Task 2.2.3
2.function
B
Decomposition Diagram
Levelled Set of DFDs• How many levels - not > 9 processes in single DFD• Different parts of system can have different level of detail• Consistency (Balancing) - inflow and outflow to process must
correspond in next level DFD• External entities,data stores,parent processes can, but need not
be repeated in child diagram• Data Stores at different levels - show data store at the highest
level where it first serves as an interface between two or more processes
Top- Down Analysis and Functional Decomposition
Carson-Plymouth Medical Devices (CPMD), as assembler of sophisticated medical products, must maintain a ready supply of high-quality components to manufacture its products. To achieve this goal, CPMD’s purchasing department checks inventory levels each day by reviewing the inventory items stock list. When the quantity-on-hand of a particular item reaches its economic reorder point, CPMD’s purchasing department places a purchase order with its supplier (supplier data is accessed through the supplier file) for that component and files a copy in the purchase order file. When a supplier delivers a shipment along with a bill of lading, shipping and receiving (S/R) receives the shipment by performing a three-step process. First, the S/R clerk verifies the shipment by accessing a copy of the purchase order and comparing it to the bill of lading. If a received item appears on the purchase order and the bill of lading, the verified bill of lading and received items are passed on to Inspection. Otherwise, the S/R clerk generates a notice of shipment error, which is sent to the supplier.Next, the inspector inspects the valid shipment items by accessing the quality criteria, from the inspection criteria folder. If the item meets all the quality criteria, the inspector adds it to an accepted items list, which is forwarded to the inventory clerk. If an item does not pass inspection, the inspector creates a notice of defective shipment, which is sent to the supplier along with the defective items. Finally, the inventory clerk updates the inventory items list by adding the current-on-hand quantity, reflecting an updated quantity.
Carson-Plymouth Medical Devices (CPMD), as assembler of sophisticated medical products, must maintain a ready supply of high-quality components to manufacture its products. To achieve this goal, CPMD’s purchasing department checks inventory levels each day by reviewing the INVENTORY ITEMS STOCK list. When the quantity-on-hand of a particular item reaches its economic reorder point, CPMD’s purchasing department places a purchase order with its supplier (supplier data is accessed through the SUPPLIER file) for that component and files a copy in the PURCHASE ORDER file. When a supplier delivers a shipment along with a bill of lading, shipping and receiving (S/R) receives the shipment by performing a three-step process. First, the S/R clerk verifies the shipment by accessing a copy of the purchase order and comparing it to the bill of lading. If a received item appears on the purchase order and the bill of lading, the verified bill of lading and received items are passed on to Inspection. Otherwise, the S/R clerk generates a notice of shipment error, which is sent to the supplier.
Next, the inspector inspects the valid shipment items by accessing the quality criteria, from the INSPECTION CRITERIA folder. If the item meets all the quality criteria, the inspector adds it to an accepted items list, which is forwarded to the inventory clerk. If an item does not pass inspection, the inspector creates a notice of defective shipment, which is sent to the supplier along with the defective items. Finally, the inventory clerk updates the INVENTORY ITEMS list by adding the current-on-hand quantity, reflecting an updated quantity.
Carson-Plymouth Medical Devices (CPMD), as assembler of sophisticated medical products, must maintain a ready supply of high-quality components to manufacture its products. To achieve this goal, CPMD’s purchasing department checks inventory levels each day by reviewing the INVENTORY ITEMS stock list.
Process Ext. Entity Input Output Data Store
check inventory inventory levels from items to reorder inventory levels Inventory list items
When the quantity-on-hand of a particular item reaches its economic reorder point, CPMD’s purchasing department places a purchase order with its supplier (supplier data is accessed through the SUPPLIER file) for that component and files a copy in the PURCHASE ORDER file.
Process Ext. Entity Input Output Data Store
create a PO supplier items to reorder, PO to supplier, inv items supplier data PO to file supplier, from Supplier file PO
When a supplier delivers a shipment along with a bill of lading, shipping and receiving (S/R) receives the shipment by performing a three-step process. First, the S/R clerk verifies the shipment by accessing a copy of the purchase order and comparing it to the bill of lading. If a received item appears on the purchase order and the bill of lading, the verified bill of lading and received items are passed on to Inspection. Otherwise, the S/R clerk generates a notice of shipment error, which is sent to the supplier.
Process Ext. Entity Input Output Data Storeverify Supplier bill of lading; verified bill PO
copy of PO of lading, notice of shipment errors to Supplier
Next, the inspector inspects the valid shipment items by accessing the quality criteria, from the INSPECTION CRITERIA folder. If the item meets all the quality criteria, the inspector adds it to an accepted items list, which is forwarded to the inventory clerk. If an item does not pass inspection, the inspector creates a notice of defective shipment, which is sent to the supplier along with the defective items. Process Ext. Entity Input Output Data StoreInspect Supplier verified bill of lading; accepted items Inspection Shipment inspection criteria list; defective Criteria
from Inspection shipment notice Criteria Folder to Supplier
Finally, the inventory clerk updates the INVENTORY ITEMS list by adding the current-on-hand quantity, reflecting an updated quantity
Process Ext. Entity Input Output Data Store
Update Accepted items updated inv levels Inv. ItemsInventory list, current inv.
levels
Verify shipment
Check inv levels
Create PO
Inspect shipment
Update Inv.
Supplier
DS1 Supplier
DS2 PO File
DS2 Inspection Criteria
DS4 Inventory Item
Notice of defective shipment
Bill of lading
P.O.
Items to reorder
Low items
Current Data
Updated data
Supplier data
New PO data
PO info
Accepted items list
Verified bill of lading
Notice of shipment error
Inspection Criteria1.
2.
3.
4.
5.
Level 0 DFD
4.1
Identify Inspection Criteria
4.2
Inspect Items
4.3
Prepare notice of defective shipment
DS1 SupplierInspection criteria
Item numbers, criteria
Defective items data
Accepted items list
Notice of defective shipment
Level-1 DFD for Inspect Shipment
Context and level 0 DFD
When parts are received from vendors, they are accompanied by an invoice. Mrs Gauron in the Receiving Dept checks the invoice against the orders file to be certain that the correct parts were delivered. If the parts were not ordered or the order was incorrectly filled, parts are returned. If the parts are correct, the inventory file is updated to reflect the new quantity of these parts. This is done by increasing the data element quantity-on-hand by the quantity-record for the part-id . Mrs Gauron then prepares the payment for the vendor. She also enters the payment transaction in the general ledger, which is maintained as the bound accounting ledger. A worker on the factory floor who needs a part requests it by submitting a requisition to the parts clerk. The information on this form is used to update the inventory file. Each week the parts clerk uses the inventory file to prepare a report listing all parts whose quantity- on- hand has fallen below the reorder point. For parts listed on the report, a purchase request form is prepared and sent to the purchasing office.
[ Hint: do not confuse the processes being performed with the people who perform them ]
Vendor
Floor
Purchasing Office
0.Inventory
System
Context level DFD
Invoice
Projected Part
Payment
Requisition
Purchase Request Form
Order File
Inventory
General Ledger5.
Check part for reorder
4.Provide
part
2.Update Part Qty
3.Pay
Vendor
1.Check invoice
6.Prepare
purchase request Floor
Purchasing office
Vendor
Invoice
Rejected Part
Payment
Payment Info
Order record
ApprovedInvoice
ApprovedInvoice
Part-id,Qty
Inv. record
Used Part info
RequisitionReorderInfo
Purchase request form
Delta Products Corporation is a major vendor of office supplies, furniture and equipment. Delta’s sales representatives call on customers to take orders. The sales rep write up the orders and turn them in to a sales order processing (SOP) clerk at the regional center. If the order items are in stock, the SOP clerk prepares a picking slip and packing list for each order. If any of the ordered items are out of stock, the SOP clerk completes an out of stock Notice forms, which notes the number of customer requiring the items and forwards it to Purchasing. A Purchasing clerk then completes a purchase order,which is mailed to a supplier. The SOP clerk notes back-ordered items on the customer’s order and forwards a copy of annotated customer order to Accounts receivable, where a A/R clerk prepares an invoice and sends it to the customer. The SOP clerk also forwards a picking slip and packing list to the warehouse, where stock price pickers fill the order,placing ordered items into boxes alongwith the packing list. The boxed items and packing list are held for delivery, usually via UPS.
• Context Diagram• Level 0 DFD• Level 1 DFD for functions related to the sales-order processing clerk
CustomerCustomerEE-1
SupplierSupplierEE-2
ProcessOrder
2.*
WriteOrder
1
Order Information
Written Order
BillCustomer
4
Invoice
Annotated Order
PurchaseInventory
5
Out of Stock Notice
PurchaseOrder
FillOrder
3
UPSUPSEE-3
Packing List&
Picking Slip
D-1 Inventory Items
UpdatedInventory
CurrentInventory
Level 0 DFD for Delta Products’ Order Fulfillment System
CheckItem
Availability
2.1
D-1 Inventory ItemsUpdated Inventory
Current InventoryWritten Order
PrepareOoS
Notice
2.3
AnnotateOrder
(backordered items)
2.2
PurchaseInventory
5
BillCustomer
4
Preparepacking list
& picking slip
2.4
FillOrder
3
Packing List & Picking Slip
Annotated Order
Out of Stock NoticeOut of Stock items order
In-Stock items order
Level 1 Process 2.0 - Process Order