1. Chapter 4 Documenting Information Systems
Yong Choi
BPA
CSUB

2. System Concept
A system exits by taking input from the environment , transforming (processing) input, and release an output
A system may be decomposed (exploded) into subsystems
Output of one subsystem may become the input of other subsystems

3. System Concept (con’dt)

4. System Decomposition (General)
No additional notes

5. Decomposition Diagram (Hierarchy Chart)

6. Example of Decomposition Diagram
No additional notes.
SoundStage Entertainment Club

7. Decomposition: Use-Case Diagram

8. Separating data and processes
Characteristic
System focus
Design stability
Data organization
State of data
Process-orientation
what, when & how to do
Limited due to change in business processes
Designed for individual applications
unstructured
Data-orientation
Operation of Data
More stable as data needs change slowly
Designed for enterprise
Controlled

9. Separating data and processes
Process-oriented approach
An IS development strategy that focuses on how and when data are moved through and transformed by an IS
Sequence of steps in the process-oriented approach:
define problem -> identify necessary decisions -> describe information needs -> determine necessary processing -> specify data needs
Data-oriented approach
An IS development strategy that focuses on the optimal organization of data, not on where or how data are used
Sequence of steps in the data-oriented approach:
define problem -> identify requirements -> develop data model for each user's data -> integrate all the data models into an overall model

10. Process Modeling with DFD
Process Modeling is a technique for organizing and documenting the structure and flow of data through a system’s processes, and the logic, policies, and procedures to be implemented by a system’s processes.
A Data Flow Diagram (DFD) is a graphical modeling tool to depict the flow of data through a system and the work or processing performed by that system.
What’s the system doing

11. Data Flow Diagrams (DFD)
Key points for modeling
How data moves through the organization
Relationships between various data flows
Storage of data
There are no FIXED rules about how a DFD should be developed…
There is no such a DFD call “CORRECT DFD”…
Expert SAs may not need much…..but definitely need for YOU!!

12. Developing a DFD

13. Simple Data Flow Diagram for Banking
Teaching Notes
We have found it useful to walk through this first DFD. Don’t be alarmed if students take exception to some of the oversimplification of the illustrated problem—it can actually contribute to the learning experience.

14. Process Logic
DFDs are effective tools for identifying processes, but are not good at showing all the detail logic inside those processes.
Not always easy to know what the lowest logical level is
However, it is better than:
Flowcharts and Pseudocode (difficult for users to understand).
No additional notes.

15. Flowchart

16. Flowchart Limitations
Complex logic: Sometimes, the program logic is quite complicated. In that case, flowchart becomes complex and clumsy.
Alterations and Modifications: If alterations are required the flowchart may require re-drawing completely.
Reproduction: As the flowchart symbols cannot be typed, reproduction of flowchart becomes a problem.
The essentials of what is done can easily be lost in the technical details of how it is done.

17. Pseudocode
This is the pseudocode for a Game of Monopoly, including one person's move as a procedure:
Main Procedure Monopoly_Game
Hand out each player's initial money.
Decide which player goes first.
Repeat
Call Procedure Monopoly_Move for next player.
Decide if this player must drop out.
Until all players except one have dropped out.
Declare the surviving player to be the winner.
Procedure Monopoly_Move
Begin one's move.
Throw the dice.
Move the number of spaces on the board shown on the dice.
If the token landed on "Go to Jail,"
then go there immediately.
Else if the token landed on "Chance" or "Community Chest,"
then draw a card and follow its instructions.
Else
follow the usual rules for the square (buying property, paying rent, collecting $200 for passing "Go", etc.).
End one's move.

18. Elements of a DFD External Entity Data Flow Process Data Store
DE MARCO & YOURDON NOTATIONS (Textbook)
External Entity
Data Flow
Process
Data Store

19. Elements of a DFD External Entity Data Flow Process Data Store
GANE & SARSON NOTATIONS (more universal)
External Entity
Data Flow 3
Process
Pay Bill
AP Clerk
Data Store

20. External Entities
SUPPLIER
An External Entity is a provider (source) or receiver (sink) of data and information of the system
External agents define the “boundary” or “scope” of a system being modeled.

21. External Entities …
An external entity (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.
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 system’s end-users or managers

22. Data Stores A data store is an inventory of data.
Accounts Receivable
A data store is an inventory of data.
A data store means “data at rest.”
A data flow means “data in motion.”

23. Data Stores … Almost always one of the following:
Persons (or groups of persons): e.g., customer
Places: e.g, cash register
Objects: e.g., product
Events (about which data is captured): e.g., sales
Concepts (about which data is important): e.g., discount
Data stores depicted on a DFD store all instances of data entities (depicted on an ERD)

24. Data Flows
DELIVERY SLIP
A Data Flow represents an input of data to a process, or the output of data from a process.
A data flow may also be used to represent the creation, reading, deletion, or updating of data in a “data store.”
A composite data flow (packet) is a data flow that consists of other data flows.
A Data Flow does not represent a document or a physical good: it represents the exchange of information in the document or about the good

25. Processes 1
Pay Bill
A Process is a work or action performed on input data flow to produce an output data flow
Use a verb to label the action performed by the process (not the name of person or department who does it as in physical DFD)
A Process must have at least one input data flow and at least one output data flow.

26. How to find each one… External Entities (EE) Processes (P)
people/organizations/things that supply information to or use information from the system
Processes (P)
actions/doing words/verbs
Data Flows (DF)
movement/exchange of information/data between external entities to processes, and processes to processes
Data Stores (DS)
store/record information/data

27. DFD using Use-Case The actor that initiates the event The use cases
External entities
The use cases
Will be handled by a process
Inputs (or triggers) & outputs and responses
Will become a flow of data
** data store is a result of data flow..thus, need naming creativity… **

28. DFD Naming Guidelines External Entity  Noun Data Flow  Names of data
Process  verb phrase
a system name
a subsystem name
Data Store  Noun

29. Guidelines for Developing DFD
Develop a list of business activities
Similar to business rules of ERD
Create the Context Diagram (we know this)
shows external entities and data flows to and from the system: conceptual DFD
Create level 0 DFD (or Diagram 0 in textbook)
shows general processes at the highest level
Create level 1 DFD (or Child Diagram in textbook)
shows more detailed processes

30. Apply logical sequence of the system..
A student (EE / DS) sends in an application form (DF) containing their personal details, and their desired course
The university checks (P) that the course is available.
If the course (DS) is available the student is enrolled (P) in the course, and the university confirms (P) the enrolment by sending a confirmation letter (DF) that they are registered for the course to the student.
Or if the course is unavailable the student is sent a rejection letter (DF).

31. 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

32. Level 0 and 1 DFD Building Procedure
Level-0 DFD
Identify what is being done between each input and its corresponding output
Identify the processes
Identify external data flows between external entities and processes
Identify internal data flows between processes and data stores

33. Tips for Level 1 and Below
Level-1 DFD’s
Sub-processes (primitive processes) of Level-0 processes
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
More than seven processes become overly complex and difficult to read

34. Context diagram for the example
External entity: Student
Process: Student Administration process application
Data Flows: Application Form, Confirmation/Rejection Letter

35. Apply logical sequence of the system..
A student (EE / DS) sends in an application form (DF) containing their personal details, and their desired course
The university checks (P) that the course is available.
If the course (DS) is available the student is enrolled (P) in the course, and the university confirms (P) the enrolment by sending a confirmation letter (DF) that they are registered for the course to the student.
Or if the course is unavailable the student is sent a rejection letter (DF).

36. Level-0 DFD External entity: Student
Processes: Check course available, Enroll student, Confirm Registration
Data Flows: Application Form, Course Details, Course Enrolment Details, Student Details, Confirmation/Rejection Letter
Data Stores: Courses, Students.
Also see the “Lemonade Stand” example from the class website

38. Rules in DFD Building
Rule 1 : Use only DFD notations to avoid confusion
Rule 2 : Use an action VERB to label a process (because a process is an action !!!)

39. Rules in DFD Building ...
Rule 3 : Must be one process associated with each data flow … M M

40. Detail Rules in DFD Building ...
Rule 3 : Must be one process associated with each data flow … M N M N

41. Detail Rules in DFD Building ...
Rule 3 : Must be one process associated with each data flow.

42. Detail Rules in DFD Building ...
Rule 4 : Shaded corner must appear in ALL occurrences of a duplicated symbol in a same diagram
CUSTOMER D3
Accounts Receivable
CUSTOMER D3
Accounts Receivable

43. Detail Rules in DFD Building ...
Rule 5 : No process without output data flow (black hole !!!)

44. Detail Rules in DFD Building ...
Rule 6 : No process without input data flow (miracle !!!)

45. Detail Rules in DFD Building ...
Rule 7 : No need for routing (without transforming) a data flow with a process (non value-added activities !!!)
Info A
Info A

46. Detail Rules in DFD Building ...
Rule 8 : Identical input, output data flows for parent and child processes (but the child processes can have their own throughputs)
See the picture in next slide

47. Detail Rules in DFD Building ...M
Context Diagram P N M 1 2 P 3 N
Level-0 Diagram

48. Detail Rules in DFD Building ...
Rule 9 : Data flows cannot split by themselves

49. Detail Rules in DFD Building ...
Rule 9 : Data flows cannot split …

50. Detail Rules in DFD Building ...
Rule 10 : A data packet can combine many data elements being transmitted at the same time to the same destination

51. Detail Rules in DFD Building ...
Rule 11 : Double-headed arrows are forbidden [in- flow (update) and out-flow (extract info) of a data store are different]

52. Common Process Errors on DFDs
Teaching Notes
Idea: Correct this diagram as an in-class exercise.
3.1.1: To correct the diagram, a data flow, ACCOUNTING DATA, should be added from the data store, MEMBER ACCOUNTS, to process
3.1.2: To fix the black hole, we might add an output data flow called NEW MEMBER ACCOUNT from process to the data store MEMBER ACCOUNTS.
3.1.3: To fix the miracle, you would need to at least add a data flow such as ACCOUNTING DATA from the data store, MEMBER ACCOUNTS, to process In all likelihood, you also need some type of triggering data flow, such as ACCOUNT FREEZE AUTHORIZATION, from a new external agent, such ACCOUNTING DEPARTMENT, to process