CM515100-1 Business Systems Analysis, Design and Construction BSADC

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CM515100-1 Business Systems Analysis, Design
and ConstructionBSADC

• Week 8

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Entity Life Histories (ELH) - the rise and fall
of data
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To Date

• We have studied
• How we can identify, record and analyse the flow
  of data through a system, using
• Dataflow Diagrams
• How we can identify, record and analyse how data
  is stored within a system, using
• Entity Relationships (LDS)
• Attributes (Data items) and Keys
• Normalisation

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The Context Diagram
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Logical Data Structures
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What is missing?

• We now need to focus on the EVENTS that
• Create an Entity Occurrence
• Prompt the amendment of an Entity Occurrence
• Signify when and how an Entity Occurrence should
  be deleted from the system records

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Aims and Objectives

• To introduce the student to the concept that
• Entities have a life history, and
• The techniques that can be employed to think
  about and record them
• At the end of this weeks study you will be able
• understand the application of ELH in systems
  analysis
• represent Entity Life History using basic notation

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The Purpose of ELH

• Identify all of the EVENTS that affect the data
  of an entity
• Identify where and when we need to interact with
  the system
• for input
• for amendment
• for deletion
• Cross check with other diagrams eg
• DFDs and ERDs

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The Life History of the Person Entity

• Born
• Lives
• Dies

• Is this all?

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The Life History of the Person Entity

• Born
• Lives
• Dies

• Named
• School
• Exam Results
• Jobs
• Married
• Children
• Retires

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The Life History of the Order Entity

• Input Sales order
• Order Life
• Delete Order

• Delivery note
• Confirm picking
• Confirm despatch
• Confirm goods delivered
• Produce invoice
• Receive payment

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Entity Life History

• Modelling the individual ELH
• Ask the question - What causes the entity
  occurrence (record in the database) to be
• Created by the system?
• Amended by the system?
• Deleted by the system?
• change its relationship?
• change its status?

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ELH Notation

• The four basic constructs
• Sequence - events follow each other in
  sequence
• Selection - one event or another will occur at
  a point in time
• Iteration - the event is repeated a number of
  times
• Special options - more later

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Sequence 1
Event 1 happens then events 2 and 3 always in
this sequence
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Sequence 2
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Selection 1
Note the O
Event 5 or 6 happens only one can happen
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Selection 2
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Selection 3
Entity
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0 Event 5
0 Event 6
Event 5 or 6 or nothing happens
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Iteration 1
Entity
Event 6 happens a number of times
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Iteration 2
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Quit and Resume
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The Entity/Events Matrix

• With the aid of the DFDs and LDS
• List entities
• List events (processes)
• Construct ELH Matrix

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The Customer Order

• Accept Sales order
• Confirm picking
• Confirm despatch
• Goods Delivered
• Produce invoice
• Receive payment

• Enter order
• Enter picking date/time
• Enter despatch date/time
• Enter Delivery date/time
• Enter invoice date
• Enter payment date

Are other entities being affected here?
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The Entity/Events Matrix
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Adding more detail to the matrix

• We can specify the events by nature on the matrix
• Create C
• Read R
• Update U
• Delete D
• You may also see
• I insert
• M modify
• D delete

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Entity /Event Matrix
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Self Study

• Read Mastering Systems Analysis and Design -
  pages 143 to 153
• Do exercises 11.5.1 to 11.5.2
• Read handout

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Next week

• The Feasibility Report

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Tutorial

• Holiday booking entity
• The student entity
• Project entity