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Lecture 9 Descriptors, Events & Event Tables INFO1409 Systems Analysis & Design Module HND Year 1 2008/9.

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Presentation on theme: "Lecture 9 Descriptors, Events & Event Tables INFO1409 Systems Analysis & Design Module HND Year 1 2008/9."— Presentation transcript:

1 Lecture 9 Descriptors, Events & Event Tables INFO1409 Systems Analysis & Design Module HND Year /9

2 2 Lecture 9 Learning Objectives At the end of this lecture you should be able to: - Explain what is meant by an event. -Identify events which trigger the system. -Draw an events table and a Use Case model

3 3 Modelling systems recap We develop a model after completing our fact finding. One way to do this is to identify Users and Processes. Once identified, we can produce Role Descriptors and Business Process descriptors.

4 4 Accountant E.G : Staff Administration system Add Staff Amend staff Calculate pay We have previously described the work of the Accountant and the processes (Use Cases) in the form of descriptors.

5 5 Using Events Tables: Another method is to use ‘Events’ which trigger business processes Recap: In lecture 2 we examined how an Event could trigger 3 business processes. The event was called “Receive Sales Order” Question: What type of event is this? (Answer given on the next slide).

6 6 A simple business model might consist of an Event 3 business processes and a result This event is a response to an external trigger

7 7 Types of event Events trigger all the processing a system does. There are three types of event: External Temporal State

8 8 External events occur outside the system and are usually initiated by a person (often called an Actor). The system is required to record details about an external event e.g.) customer places an order. Or the system is required to produce something in response to the request: e.g.- customer rings to follow up/chase an order.

9 9 Actors The people who initiate these responses from the system are called Actors. -They are carrying out a role (hence actor). …When you place an order you are taking on the role of a customer. …If you are requesting management information you are taking on the role of a particular job task.

10 10 Typical external events Actor wants some information - e.g. customer enquires about an order they have placed. Data needs to be updated- e.g. employee changes address. Management wants some information-e.g. manager want to know who has holidays booked.

11 11 Temporal Events Temporal events are triggered by a specific time being reached. Many systems produce daily, weekly, monthly and annual reports. These reports are triggered when a specific date and time are reached. Some events are triggered after a certain amount of time has passed (e.g.) reminder produced 2 weeks after bill was sent.

12 12 Typical Temporal Events Internal outputs required, Management reports, e.g.) summary of all orders. Operational reports (detail of daily operation) Internal statements and documents (including payroll) External outputs required, e.g.) Statements,bills and reminders

13 13 State events State events are triggered by a certain state/particular condition becoming true. (Similar to temporal events except that the time cannot be defined.) e.g.) Reorder stock because the number of items in stock have reached a specific minimum level (re-order level), or e.g.) Bank sends out a letter to their customer as their account has gone overdrawn.

14 14 Identifying Events …can be difficult! Following the process through can identify the sequence of events. If there is no time delay between two or more interactions then they are the same event, otherwise they are different events.

15 15 Events we are not interested in The analyst is not interested in events that the do not normally concern the users. These are dealt with during design, Logging on Passwords Backups The other type of events we are not interested in just yet are the error routines. It helps to think that everything is perfect and concentrate on events that are required in a perfect world (Perfect World assumption).

16 16 Example Look at the following sequence of occurrences at a hotel- identify the events Look for things that occur together without any time delays. What are the events ? What do they involve? What would you call the events?

17 17 Example: hotel occurrences 1. Customer contacts the hotel to see if they have a room free for the following Saturday. 2. The clerk checks the room bookings and finds a free room. 3. Customer accepts the room and gives their personal details (e.g. name, address, etc.) to the clerk. 4. The customer pays the deposit by credit card. 5. The clerk updates the system to show the room is no longer free on Saturday and that it is booked to the customer. 6. The customer rings the following day to order flowers for the room. This is added to the room booking for inclusion on the bill.

18 18 Example: hotel occurrences 4. The customer turns up on Saturday and gives their name. 5. The clerk uses the system to find the room number and gives the customer their room key. 6. The clerk records that the room is now occupied. 7. On Sunday the customer is leaving the hotel. 8. The bill is calculated by the clerk. 9. The customer pays the bill. 10. The clerk records that the room is no longer occupied and that the customer has paid.

19 19 Looking at each event For each event the analyst must determine the: Trigger Source Activity/Use Case Response Destination

20 20 Trigger How does the system know the event has occurred?  For external events…data enters the system. For temporal events…it is the date or time. For state events… it is the condition that has been met.

21 21 Source Source is: for external events only usually the actor; in other words who is supplying the data which will be typed in.

22 22 Activity or Use Case What process does the system carry out in response to the event trigger? Remember: Case when the system is used to produce…..

23 23 Response and Destination Response: What output (if any) is produced by the system? Destination: What actor gets this output?

24 24 Building an Events Table An Events Table can be built using one row for each event. We call the first event ‘customer makes booking’ we can call our Use Case this We can tell from our description that an event is happening and that we need the customer to trigger it and an Actor to perform the process.

25 25 Events Table: hotel booking EventTriggerSourceUse CaseResponseDestination Customer makes booking customer enquiry custome r create new booking room booking confirm- ation customer and clerk

26 26 Events tables to Use Case diagrams We can use the Events table to define the elements of a Use Case model. Question: How does this work? Answer : Our Events table has given us a Use Case -Create new booking

27 27 Recap on Use Case model elements The symbols we can use are as follows: Actor Association Use Case Use Case label stereotype

28 28 Actors and Use Cases Our Event table tells there are 2 Actors or ‘Inter-actors’ involved with the system for the first event. 1. The Booking Clerk 2. The customer (who provides the trigger and necessary input information)

29 29 Event shown as a Use Case model Create new booking Booking Clerk Customer Remember this is just a fragment!! Illustration

30 30 Over to you.. It is now your turn to complete the Hotel occurrences example. Complete the table, and then translate it into a Use Case diagram. Remember that practice makes perfect

31 31 Answers 1.Customer contacts the hotel for a free room 2.Clerk checks room availability 3.Customer gives name and address 4.Customer pays deposit 5.Clerk updates system to show room booked 6. Customer rings to order flowers 7. Customer turns up 8. Clerk find room number and gives key 9. Clerk records room as occupied 10. Customer leaves 11. Bill calculated 12. Customer pays bill 13 Clerk records room empty and customer paid. Customer Makes Booking Customer Orders service Customer Checks in Customer Checks out

32 32 Events Table: hotel booking EventTriggerSourceUse CaseResponseDestination Customer makes booking customer enquiry custome r create new booking room booking confirm- ation customer and clerk

33 33 A simple business model might consist of an Event 3 business processes and a result Could you also construct an events table and Use Case diagram from this example?

34 34 Summary You should now know: What is meant by an event. The different types of events and be able to give an example of each. What is meant by a trigger, source, use case, response and destination. How to draw an events table. How to draw a simple Use Case example from your Events table.

35 35 References Systems Analysis & Design Shelley Cashman and Rosenblat 6 th Ed. Thomson (2006) Eva and Skidmore (2004). Introducing Systems Development. Palgrave Macmillan. Satzinger JW, Jackson RB and Burd SD (2004). Systems Analysis and Design in a Changing World. 3 rd edition. Thomson.


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