1. Modeling System Events Adapted from: Systems Analysis and Design in a Changing World, 2nd Edition by John W. Satzinger, Robert Jackson and Stephen Burd published by Course Technology

2. Events and System Requirements Two key concepts to model:  Events  Things Event – an occurrence at a specific time and place, that can be described and is worth remembering  E.g. customer placing an order, shipping identifies a backorder, nuclear reactor goes to meltdown When defining system requirements it is useful to begin by asking what events occur that will affect the system being studied  What events will occur that the system will have to respond to?  Allows you to focus on external environment to keep you at high level view of system (not the workings of it)

3. Events (cont.)  Also allows you to focus on the interfaces of the system to outside people and systems  End users can easily describe system needs in terms of events that affect their work, so useful when working with users  Gives a way to divide (or decompose) the system requirements so you can study each separately (complex systems need to be decomposed based on events)

5. Background to Event Concept Structured analysis adapted to real-time systems in the early 1980’s  E.g. process control system, reactors, aerospace etc.  Events like “chemical vat is full”, “boiler overflowing”  System must respond to these types of events immediately  Extended to business applications since they have become more interactive  Information engineering approach now uses it  Very important in object-oriented approach

6. Types of Events External Event  An event that occurs outside the system  usually initiated by an external agent or actor (a person or organization that supplies or receives data from the system)  Classic example of an external agent: a customer  Event might be that the customer wants to place an order  Naming events: Include the external agent in the name E.g. events: “Customer places order”, “Management checks order status”,”Customer reports change of address”

7. External Events Checklist  External agent wants something resulting in a transaction  External agent wants some information  Data changed needs to be updated  Management wants some information Temporal Events  An event that occurs as a result of reaching a point in time eg. Payroll systems produce a paycheck every two week (or once a month)  Could be reports to management generated regularly  System automatically produces reports etc. at right time (so no external agent needed)  E.g. temporal event “Time to send late payment notice” (e.g. timed as event 15 days after billing date)

8. Temporal Events Checklist  Internal outputs needed Management reports (summary or exception) Operational reports (detailed transactions) Statements, status reports (including payroll)  External outputs needed Statements, status reports, bills, reminders State Events  An event that occurs when something happens inside the system that triggers the need for processing  E.g. the sale of a product results in an adjustment in the inventory (event “Reorder point reached)  This state change might occur as a result of external events or to temporal events (so could be similar to temporal event, but point in time can’t be defined

9. Identifying Events Events versus conditions and responses  Can be difficult to distinguish between an event and the sequence of conditions that lead to it (e.g. events leading to buying a shirt)  Also may be hard to distinguish between an external event and the system’s response (e.g. customer buys shirt, system requests credit card number – the customer buying the shirt is the event)  Way to determine if an occurrence is an event Ask whether any long pauses or intervals occur (I.e. is the system at rest for another transaction to complete? Once a transaction starts there are no significant stops till done

10. Tracing the Sequence of Events  Can trace the sequence of events for a specific external agent or actor  The analyst must think of all the possible transactions resulting from one new customer Customer wants a catalog Customer asks for information about availability Customer places an order Customer wants to check status of an order Customer wants to change his/her address Customer may want to return an item

12. Technology-Dependent Events and System Controls  System controls: checks or safety procedures put in place to protect the integrity of the system Logging on to a system (for security reasons) Controls for keeping integrity of a database  To help decide which events apply to controls we assume that technology is perfect (never the case!)  During analysis we should focus on events that are required under “perfect” conditions -- “perfect technology assumption”  It is during design phase that we deal with other issues and events from a “non-perfect world” point of view, e.g. events like “Time to back up the database”

13. External Events for a Customer Support System Look at all the people and organizations that want the system to do something: Customer wants to check on item availability Customer places an order Customer changes or cancels order Customer or management wants to check order status Shipping fulfills orders Shipping identifies back order Customer returns item Prospective customer requests catalog Customer updates account information Marketing wants to send promotional materials to customers Management adjusts customer charges (corrects errors) Merchandising updates catalog Merchandising creates special product promotion Merchandising creates new catalog

14. Temporal Events for a Customer Support System Look at all the regular reports and statements that the system must produce at certain times: Time to produce order summary reports Time to produce transaction summary reports Time to produce fulfillment summary reports Time to produce prospective customer activity reports Time to produce customer adjustments/concession reports Time to produce catalog activity reports

15. Looking at Each Event Event Table: A table that lists events in rows and key pieces of information about each event in columns  The trigger: an occurrence that tells the system that an event has occurred (either the arrival of data needing processing or of a point in time)  The source: an external agent or actor that supplies data to the system  The activity: behavior that the system performs when an event occurs  The response: an output, produced by the system, that goes to a destination  The destination: An external agent or actor that receives data from the system