1. The Flow Model REVIEW : Every computer-based system is an
information transform ....
computer
based
system
input
output

2. Flow Modeling Notation
external entity
process
data flow
data store

3. External Entity A producer or consumer of data
Examples: a person, a device, a sensor
Another example: computer-based
system
Data must always originate somewhere
and must always be sent to something

4. Process A data transformer (changes input to output)
Examples: compute taxes,
Data must always be processed in some
way to achieve system function
determine area,
format report, display graph

5. Data Flow Data flows through a system, beginning
as input and be transformed into output.
base
compute
triangle
area
area
height

6. Data Stores Data is often stored for later use. look-up sensor data
sensor #, type,
location, age
look-up
sensor
data
report required
type,
location, age
sensor number
sensor data

7. The Data Flow Hierarchyb x P y
level 0 c p2 a f p1 b p4 d 5 g p3 e
level 1

8. DFD: A practical example
Launched Dec. 11, 1998, the Climate Orbiter plunged too steeply into the Martian atmosphere Sept. 23, 1999, and either burned up or crashed. In an initial failure report released Oct. 15, 2000 the review board blamed the navigation error on a communications foul-up between NASA's Jet Propulsion Laboratory and prime contractor Lockheed Martin.

11. Entity Relationship Diagram Cardinalities
Sales-
person
Car
Type
Customer
Order
Vendor
Inventory
Assigned
Places
Supply
Entity
Relationship 1 M
Entity Relationship Diagram (ERD) - is a documentation technique to represent the relationship between entities in a system.
The REA model version of ERD is widely used in AIS. REA uses 3 types of entities: resources – autos, inventory, college major
Events – ordering inventory, receiveing cash payment, shipment, selecting a major
Agents – salesperson customer, student
resources (cash, raw materials)
events (release of raw materials into the production process)
agents (inventory control clerk, vendor, production worker)
Rectangles – entities
Diamonds – relationships verbs – have inherent cardinalities represents the numerical mapping between entities:
one-to-one 1:1 one salesperson is assigned to one auto
one-to-many 1:M one customer may have placed many orders
many-to-many M:M many inventory items are purchased from many vendors
DFD – model the processes of a system – each data store in DFD – corresponds to data entity in ER diagram
ER diagrams model the data that is used or affected by the system
(see fig 2-15 that illustrates ER diagram for the DFD illustrated in fig 2-13). 23

12. Documents Flowcharts…
illustrate the relationship among processes and the documents that flow between them
contain more details than data flow diagrams
clearly depict the separation of functions in a system
Flowcharts explain how, where and by whom processes are accomplished
Document flowcharts – created by following the hard copy of bus forms used by a company (purchase order, customer order) from beg to end.
Internal entities – that perform data process of some sort – presented as columns in a doc flowchart
See other symbols processing oval, source document, hardcopy file, accounting journals 26

13. Symbol Set for Document Flowcharts
Terminal showing source
or destination of documents
and reports
Calculated batch total
Source document or
report
On-page connector
Manual operation
Off-page connector
Other symbols – start/end process of oval
File for storing source
documents and
reports
Description of process
or comments
Accounting records
(journals, registers,
logs, ledgers)
Document flowline 27

14. Sales Department
Credit Department
Warehouse
Shipping Department
Customer
Customer
Order
Prepare
Sales
Orders
Sales
Order #1
Sales
Order #1
Sales
Order #1
Sales
Order #1
Source data?
Reference data?
Storage data?
Data flows?
First Stages in Constructing Document Flowchart Showing Areas of Activity

15. Finished Document Flowchart Showing Areas of Activity
Sales Department
Credit Department
Warehouse
Shipping Department A
Sales
Order #1
Customer
Sales
Order2
Customer
Order
Checks
Credit
Sales
Order 4
Credit
Records
Picks
Goods
Stock
Records
Sales
Order3
Prepare
Sales
Orders
Signed Sales
Order #1
Picks
Goods
Customer
Order
Sales
Order2
Sales
Order #1
Sales
Order #1
Sales
Order #1
Sales
Order #1
Sales
Order 4
Sales
Order3
Signed Sales
Order #1 N
Sales
Order2 N
Distribute
SO and
File A
Customer
Order
Customer
Sales
Order 4
Signed Sales
Order #1
Finished Document Flowchart Showing Areas of Activity
Sales
Order3
Sales
Order2 N

16. System Flowcharts…
are used to represent the relationship between the key elements--input sources, programs, and output products--of computer systems
depict the type of media being used (paper, magnetic tape, magnetic disks, and terminals)
in practice, not much difference between document and system flowcharts 28

17. Modern systems Legacy systems
client-server based and process transactions in real time
use relational database tables
have high degree of process integration and data sharing
some are mainframe based and use batch processing
Legacy systems
mainframe-based applications
batch oriented
early legacy systems use flat files for data storage
later legacy systems - hierarchical and network databases
data storage systems promote a single-user environment that discourages information integration

18. Updating Master Files: Primary Keys (PK) and Secondary Keys (SK)
Modern Systems versus Legacy Systems
Modern systems characteristics:
client-server based and process transactions in real time
use relational database tables
have high degree of process integration and data sharing
some are mainframe based and use batch processing
Legacy systems characteristics:
mainframe-based applications
batch oriented
early legacy systems use flat files for data storage
later legacy systems use hierarchical and network databases
data storage systems promote a single-user environment that discourages information integration
Some firms employ legacy systems for certain aspects of their data processing.
Accountants need to understand legacy systems.

19. Database Backup Procedures
Destructive updates leave no backup.
To preserve adequate records, backup procedures must be implemented, as shown below:
The master file being updated is copied as a backup.
A recovery program uses the backup to create a pre-update version of the master file.

20. Batch Processing
A batch is a group of similar transactions that are accumulated over time and then processed together.
The transactions must be independent of one another during the time period over which the transactions are accumulated in order for batch processing to be appropriate.
A time lag exists between the event and the processing.
Computer-Based Accounting Systems Two broad classes of systems:
batch systems
real-time systems
Batch size- function of volume of transactions, competitveness of industry, normal frequency of errors , financial implic of an undetected error and costs of processing.
Several sums are calculated at the initial transact grouping (i.e. total sales, total customer number) throughout process these totals checked and verified against initial totals – ensure no transaction lost, added, included erroneously 32

21. Batch Processing/Sequential File
Unedited
Transactions
Sales
Orders
Keying
catches clerical errors
Errors
Edit
Run
correct errors and
resubmit
Edited
Transactions
rearranges the transaction data by
key field so that it is in the same
sequence as the master file
Sort
Run
Transactions
Steps in Batch Processing/Sequential File
Keystroke - source documents are transcribed by clerks to magnetic tape for processing later
Edit Run - identifies clerical errors in the batch and places them into an error file
Sort Run - places the transaction file in the same order as the master file using a primary key
Update Run - changes the value of appropriate fields in the master file to reflect the transaction
Backup Procedure - the original master continues to exist and a new master file is created
Old Master
(father) AR
Update
Run
changes the values in the master file to
reflect the transactions that have occurred AR
Transactions (eventually transferred to an archive file)
New Master
(son) 42

22. Advantages of Batch Processing
Organizations can increase efficiency by grouping large numbers of transactions into batches rather than processing each event separately.
Batch processing provides control over the transaction process via control figures. 33

23. Real-Time Systems…
process transactions individually at the moment the economic event occurs
have no time lag between the economic event and the processing
generally require greater resources than batch processing since they require dedicated processing capacity; however, these cost differentials are decreasing
Often have longer systems development time 34

24. Why Do So Many AIS Use Batch Processing?
AIS processing is characterized by high-volume, independent transactions, such are recording cash receipts checks received in the mail.
The processing of such high-volume checks can be done during an off-peak computer time.
This is one reason why batch processing maybe done using real-time data collection.

26. Context diagram
Highest level DFD.
Has data flows, external entities, one process (system in focus) and no data stores.
Shows the system boundary and interactions with external entities.
External entity   - Student
Process            - Student Administration process application
Data Flows        - Application Form, Confirmation/Rejection Letter

28. System/Level 0 DFD
External entity   - Student
Processes         - Check available, Enroll student, Confirm Registration
Data Flows        - Application Form, Course Details, Course Enrolment Details, Student Details,    Confirmation/Rejection Letter
Data Stores       - Courses, Students.

29. Level 0

30. This System/Level 0 DFD raises some questions:
 Q. The Data Store Courses has only data flows entering it, how does the data get stored in the first place?
Q. The process Enroll Student has many different data flows entering into and leaving it, how can we model this process in more detail?
A. This DFD is part of a larger, higher level DFD that models more than just the enrolment process. There must be another DFD that stores course details, eg the university’s course development process.
A. Develop a more detail, lower level DFD for this process, that shows the processes that make up this process

31. For a local city council, letters of complaint received from rate payers are entered into a complaints master file by the City Manager’s office. The date, department code, and a complaint description are stored for each letter. Weekly reports are produced from the complaints master file and given to the City Manager. Two weekly reports are produced: a department summary and a detail list.
context level DFD (level 0) can be produced…

33. Is there something missing from this scenario?
Yes,  the council should really  acknowledge the letter of complaint.