1 btec hnc systems support castle college 2007/8 systems analysis lecture 7 descriptors events...

1BTEC HNC Systems Support Castle College 2007/8

Systems Analysis

Lecture 7

DescriptorsEvents

Events Tables


Lecture 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


Modelling Systems Recap

• We develop a model after completing fact finding

• One way to do this is to identify Users and Processes

• Once identified, we can produce Role Descriptors and Business Process descriptors


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?


A simple business model might consist of an Event 3 business processes and a result

This event is a response to an external trigger


Types of Event

• Events trigger all the processes within a system

• There are three types of event:

• External

• Temporal

• State


External Events

• Occur outside the system and are usually initiated by a person

• 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)


Typical external events

• Actor wants some information

– e.g. employee takes a call from a customer enquiring 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


Temporal Events

• 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


Typical Temporal Events

• Internal outputs required

– Management reportse.g. summary of all sales

– Operational reports (detail of daily operation)

– Internal statements and documents (including payroll)

• External outputs required

– e.g. Statements,bills and reminders


State Events

Triggered by a certain state/particular condition becoming true

(Similar to temporal events except that the time cannot be defined)

e.g. Re-order 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


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


Events we are not interested in

• Events that the do not normally concern the users. These are dealt with during designe.g. Logging on, Passwords, Backups

• Error routines (not yet…)

– Perfect World assumption – It helps to think that everything is perfect and concentrate on events that are required in a perfect world


Activity – practise

• 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?


Activity: Hotel occurrences1. Customer contacts the hotel to see if they have a

room free for the following Saturday2. The clerk checks the room bookings and finds a

free room3. 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 card5. 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


Activity: Hotel occurrences7. The customer turns up on Saturday and

gives their name8. The clerk uses the system to find the room

number and gives the customer their room key

9. The clerk records that the room is now occupied

10.On Sunday the customer is leaving the hotel11.The bill is calculated by the clerk12.The customer pays the bill13.The clerk records that the room is no longer

occupied and that the customer has paid


Examine & Document Events

• For each event the analyst must determine the:

– Trigger

– Source & Actor

– Activity/Use Case

– Response

– Destination


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 (state has changed)


Source

• The source is:

– for external events only

– in other words who is supplying the data which will be typed in

– Might be the actor or someone interacting with the actorNB Note the difference!


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…


Response and Destination

• Response:

– What output (if any) is produced by the system

• Destination:

– What actor gets this output?


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 ‘create new booking’

• 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


Events Table: hotel booking

• Event: Customer makes booking

• Trigger: Customer Enquiry

• Source: CustomerActor: Hotel Clerk

• Activity (Use Case): Create new booking

• Response: Room booking confirmation

• Destination: Hotel Clerk and Customer


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


Recap on Use Case model elements

The symbols we can use are as follows:

Actor

Association

Use CaseUse Case label

<<includes>>


Actors and Use Cases

Our Event table tells there are 2 Actors or ‘Inter-actors’ involved with the system for the first event

Only the Booking Clerk interacts directly with the system

1. The Booking Clerk

2. The customer (who provides the trigger and necessary input information)


Use Case model of the event

Remember this is just a fragment!

Hotel System

Create New Booking

Clerk


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


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


Events & Use Cases Practise

Could you also construct an events table and Use Case diagram from this example?


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


References• Systems Analysis & Design Shelley

Cashman and Rosenblat 6th 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. 3rd edition. Thomson

1 btec hnc systems support castle college 2007/8 systems analysis lecture 7 descriptors events...

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