1. data flow diagrams

2. data flow diagrams
shows how data moves through an information system but does not show program logic or processing steps
provides a logical model that shows what the system does, not how it does it

3. data flow diagrams notation
use four basic symbols that represent processes, data flows, data stores, and external entities
Gane and Sarson symbol set
Yourdon symbol set
referenced by using all capital letters for the symbol name

4. DFD notation Gane & Sarson Yourdon EXTERNAL EXTERNAL ENTITY ENTITY
DATA FLOW
DATA FLOW
Gane &
Sarson
PROCESS
Yourdon
PROCESS
DATA FLOW
DATA FLOW
DATA STORE
DATA STORE

5. DFD notation process symbol data flow symbol
receives input data and produces output that has a different content, form, or both
contain the business logic, also called business rules
referred to as a black box
data flow symbol
represents one or more data items

6. DFD notation data store symbol external entity symbol
represent data that the system stores
logical representation (physical characteristics of data store are unimportant)
external entity symbol
represents the source or sink of data

7. modeling with DFDs: basic steps
step 1: draw a context diagram
context diagram – represents the system as a single process (process 0)
step 2: draw a diagram 0 DFD
diagram 0 - exploded view of process 0; zooms in on the context diagram and shows major processes, data flows, and data stores; must retain all the connections that flow into and out of process 0

8. modeling with a DFD: basic steps
step 3: draw the lower-level diagrams
functional decomposition of diagram 0
observe leveling – use a series of increasingly detailed DFDs to describe the information system
observe balancing – maintain the input and output data flows of the parent DFD on the child DFD

9. modeling with DFDs guidelines for drawing DFDs
context diagram should fit 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 not cross lines
provide a unique name and reference number for each process
obtain as much user input and feedback as possible

10. modeling with DFDs other syntactic rules
avoid the following combinations of data flow and process
spontaneous generation
black hole
gray hole
an external entity should be connected by a data flow to a process only
data stores cannot be connected to each other

11. modeling with DFDs other concepts naming conventions
conservation of data
diverging data flows
converging data flows
composite data flow
control flow (e.g., time)

12. Example: Context Diagram
GRADING
SYSTEM
GRADED WORK
STUDENT
RECORDS
SYSTEM
STUDENT
CLASS LIST
SUBMITTED WORK
FINAL GRADE
GRADE REPORT
GRADE PARAMETERS
INSTRUCTOR

13. Example: Diagram 0 STUDENT RECORDS ASSIGN GRADE SYSTEM FINAL STUDENT2
GRADE
STUDENT
WORK 3
STUDENT
RECORDS
SYSTEM
STUDENT
GRADE
FINAL
GRADE
CLASS
LIST
GRADING
DETAIL
SUBMITTED WORK
GRADED WORK
ESTABLISH
GRADEBOOK 1
CLASS
GRADEBOOK
GRADEBOOK D1
STUDENT
CLASS DETAIL
GRADE PARAMETERS 4
INSTRUCTOR
PRODUCE
GRADE
REPORT
GRADE REPORT

14. DFD levels Context diagram Level 0 diagram Level 1 diagram

15. 4-model approach (classical)
Current
Proposed
Logical
physical aspects of system are removed as much as possible;
current system is reduced to data and processes that transform them
includes additional functions;
obsolete functions are removed; inefficient data flows are reorganized
Physical
processes labels include the technology (people or systems) used to process the data;
data flows and data stores are labeled with the actual name of the physical media on which data flow or in which data are stored
represents the physical implementation of the new system

16. data dictionary
data elements must be documented in a data dictionary so that clear, comprehensive information about the data and processes that make up the system are stored

17. data dictionary data flow attributes name or label description
alternate name(s)
origin
destination
data structure
volume and frequency

18. data dictionary data store characteristics data store name or label
description
alternate name(s)
data structure
volume and frequency

19. data dictionary process characteristics process name or label
description
process number
process description

20. data dictionary external entity characteristics entity name
description
alternate name(s)
input data flows
output data flows

21. data dictionary to document attributes, a data structure is used
data structure – specific arrangement of data attributes that define a data store or a single instance of a data flow
notation = +
{ }
[ ] ()

22. data dictionary: example
ORDER = ORDER NUMBER + ORDER DATE +
[CUSTOMER NUMBER|CORPORATE ACCOUNT] +
SHIP ADDRESS + BILL ADDRESS + {PRODUCT} +
AMOUNT
PRODUCT = PRODUCT NUMBER + DESCRIPTION +
QUANITY ORDERED + PRICE + EXTENDED PRICE
SHIP ADDRESS = ADDRESS
BILL ADDRESS = ADDRESS
ADDRESS = (POBOX NUMBER) + STREET + CITY +
[STATE|PROVINCE] + (COUNTRY) + ZIPCODE
ORDERS = {ORDER}

23. decomposition diagram
depicts the partitioning of the system into logical subsystems or processes
shows the top-down functional decomposition of a system
used as a planning tool for the DFD
also known as a hierarchy chart

24. decomposition diagram

25. process description describes the logic of primitive processes
may be represented in the following forms:
structured English
decision table
decision tree

26. process description structured English
use the three logical building blocks
sequence
selection
iteration
use indentation for readability
use standard terms used in the data dictionary and specific words that describe the processing rules

27. process description structured English examples
Profits = Revenues - Expenses
Generate Inventory Report
Add Product record to Products
IF Customer Not in Customers
THEN Add Customer to Customers
ELSE Add Current Sale to Customer’s Total Sales
Add Total Sales to Customer balance in Customers
FOR EACH Customer in Customers
Delete Customer with matching Customer ID

28. process description decision tables
alternative way to describe business rules or processing that involve a complex set of conditions
shows a logical structure, with all possible combinations of conditions and resulting actions
rows represent conditions and possible outcomes; columns indicate which combinations of conditions result in specific actions
combination of conditions may result in more than one outcome

29. process description decision tables example Conditions and Actions
Rule 1
Rule 2
Rule 3
Rule 4
type of check
personal
payroll
check amount > 1000
yes - no
company accredited by X
cash the check X
do not cash the check

30. process description decision trees
Graphical representation of the conditions, actions, and rules found in a decision table
choice between a decision table or decision tree is a matter of personal preference

31. process description
decision trees
example

32. other process analysis tools
event-driven approach

33. use case
analysis tool used to describe a business task and how the user (actor) interacts with the system to accomplish the task
may be represented in narrative or graphical form
no standard template for documenting detailed use cases
analysts are encouraged to use templates that work for them or the project they are on

34. use case example Name: Place New Order Use-Case ID: UC123
Source: Requirement 1.00
Description: A club member submits a new order for products. The member’s account standing is validated. When the availability of products is verified, a packing order is sent to the warehouse for it to prepare the shipment. Back orders are created for products not in stock. On completion, the member is sent an order confirmation.

35. use case example
Precondition: The party making the order must be a member
Trigger: A new order is submitted
Basic flow: Member provides order and payment information. All information are verified ….
Result: An order confirmation is generated and sent to the club member

36. use case sections Use Case Name Iteration Description Preconditions
Triggers
Basic course of events
Alternative paths
Postconditions
Business rules
Notes
Author and date
Additional sections such as assumptions, exceptions, recommendations, technical requirements

37. event-response list
depicts the business events that the system must respond to
employ use case analysis
contains information on:
actor that initiates the event
event
trigger or input
response or output

38. event decomposition diagram
map the events to the decomposition
serves as an outline for the lower-level data flow diagrams

39. system diagram merged events depicted in the data flow diagram
a single diagram may represent the entire system
may be a collection of DFDs representing a set of events for a major component of the system (e.g., a process in diagram 0)

40. modern structured analysis
draw the context DFD of the proposed system
make the corresponding functional decomposition diagram and diagram 0
create an event-response or use-case list
draw an event DFD for each event *
merge event DFDs into a system diagram
draw detailed, primitive DFDs for the more complex events
update the data dictionary
make the process descriptions