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

Flow Modeling Notation external entity process data flow data store

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

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

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

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

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

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.

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

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

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

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

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

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

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

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.

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.

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

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

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

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

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.

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

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.

Level 0

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

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…

   

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