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Entity Life Histories Model the system from the viewpoint of how information is changed. Diagrammatic representation of the life of an entity from creation to deletion Permitted sequence of events that can change an entity occurrence Part of the Entity-Event Modelling technique Purpose of Entity Life Histories Analysis - to show that all the update processing and states of entity occurrences have been considered Design - to help in program specification Leads to Effect Correspondence Diagrams for each event show the correspondence between its effects on entities used to define Update Process Models (program designs)
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Events in the Life of an Entity
An event causes a consistent and complete set of changes to information held in the system. Each occurrence of an entity will be affected by one or more events M. Moneybags Account P. Penniless Account Account opened Account Opened Cash Deposit £2000 Pay deposit £500 Cheque Cashed £20 Cheque Cashed £200 Direct Deposit £1000 Cheque Cashed £300 Cheque Cashed £20 Cheque Cashed £300 Direct Deposit £2000
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Sample ELH for a Bank Account
Entity Life Histories show all the events that have an effect on an entity during its life Diagram is generic i.e. valid for any account at the bank Bank Account Account Opened Account Life Account Closure Account Deletion Balance Change * o o Credit Debit
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EVENT Something that triggers a process to update system data
May have an effect on several entities Matrix shows effects of events on entities Entities Bank Account Effect of event on Customer Transaction entity is: Creation C Modification M Deletion D Events Account Opened C C Credit M C Debit M C Account Closure M Account Deletion D
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ELH Notation Bank Account Entity name Account Opened Account Life
Closure Account Deletion Nodes Balance Change * Events having an Effect on the Entity o o Credit Debit
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Sequence Entity X A B C D 'A' will always be the first to occur, followed by 'B', 'C' and 'D' in that order No other sequence is permitted No indication is given of time intervals between the boxes in a sequence
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Selection Events or nodes that are alternatives at a particular point in the entity life history Selection shown by a box with a circle in the top right corner Occurrence of entity X created by any one of three events: E, F or G Entity X A B C D o o o E F G
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Selection (continued)
If one of the options is “do nothing,” a 'null' box may be added: 'Null' box does not represent an effect or node Indicates nothing is happening If the 'null' is selected, the life continues directly to the next node or event A o o o o E F G
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Iteration Event or node may be repeated any number of times at the same point in a life An occurrence of the iteration must be complete before the next begins Shown by an asterisk in the top right hand corner of a box Event H may affect the entity any number of times NB. 'Any number of times' includes zero! Entity X A B C D o o o * E F G H
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Parallel Structures and Quits and Resumes
Occasionally required Can manage without, but useful to simplify structure Used in the situation where events or nodes occur in no predictable sequence Does not show concurrency Shown as a horizontal parallel bar on the ELH diagram
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Parallel Structures Event 'N' may affect the entity a number of times during the sequence of K, L and M. Entity X A B C D o E o F G o H * I J K L M N * Node 'I', representing the sequence, and the node 'J', representing the iteration, are shown under the parallel bar
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Diagram Without Parallel Structure
The previous ELH can be drawn without the parallel structure Iteration of 'N' must be repeated several times Parallel Structure is probably easier to understand Entity X A B J K J L J M J D o o o * * * * * E F G H N N N N
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Quit and Resume Quit from one part of an ELH to Resume in another part
If the quit event occurs, then instead of processing the event marked with the Q, the life jumps to the quit event which is marked R After event B occurring, instead of the normally occurring next event C, event E can occur Y A 1 D E R1 Possible event sequences are: abcbcde, ade, abe, abcbe Known as a disciplined conditional quit 2 * C B Q1
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Illegal Unconditional Quit
Unconditional quit where the quit event must always be followed by the resume effect Different from the disciplined conditional quit shown previously Can always be avoided by redrawing the structure Entity X A B D C E o F o G o H * Illegal in SSADM I J K L M N *
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Equivalent Diagram to SSADM Standards
Two new nodes, P and Q, ensure that each parent node has children of only one type. Entity X P D o o F Q A B C o o E G H * I J K L M N *
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Random Quits and Backward Quits
Quit backwards (reversion) to Account Life if Account Re-opened (Q1) Bank Account Account Account Account Possible Account Opened Life Closure Re-open Deletion R1 Balance Change * Account o o Re-opened Q1 o o Death Credit Debit R2 Structure Q2: Quit from anywhere on Customer death to R2 Customer Customer Death Deletion Random Quit on Customer Death to Death Structure (R2)
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Combining the Components
A node cannot be a “parent” to more than one type of structure. This structure is incorrect because: Node X, combines (“parents”) a selection (A and B) with a sequence (A, B, and 2) Node 2 combines a selection (C and 4) and an iteration (F) with a parallel structure Node 4 combines two iterations (D and E) with a sequence. X A O B O 2 C O 4 O F * D * E *
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Corrected Version to SSADM Standards
X 1 2 A o B o 3 7 C o 4 o F * Node X parents a sequence; Node 2 parents a parallel structure; Node 3 parents a selection; Node 4 parents a sequence; Nodes 5, 6, and 7 parent iterations. 5 6 D * E *
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Effect Qualifiers (Optional Effects)
Where one event can affect an entity occurrence in two or more ways Bank Account Account Opened Account Life Account Closure Account Deletion Balance Change * e.g. The event “Debit” will have different processing if account is overdrawn rather than in credit Credit Debit Debit Debit credit) (account (account in Effect Qualifiers (shown in brackets) distinguish between two different effects of the same event (Debit) overdrawn) Optional Effects
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Entity Roles (Simultaneous Effects)
When one event occurrence affects more than one entity occurrence (of the same type) in different ways E.g. a Bank Account may be closed by transfer to another account One event occurrence “Transfer”, two entity occurrences affected account being closed and account being opened Simultaneous effects of one event shown by role names in [square brackets] Bank Account Account Account Account Account Opened Life Closure Deletion Cheque or o Transfer o Transfer o Final o Cash Credit [New Account] [Closed Account] Withdrawal Entity Roles
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Operations Operations added to Entity Life Histories
Operations show the processing performed on the data Each operation must change an attribute value in the entity occurrence or a relationship occurrence Operations follow a specified syntax (considered later) Operations identified by number in small square box attached to entity Operations list shown beside Entity Life History Bank Account Account Account Account Account Deletion Opened Life Closure 1 2 6 Balance * Change o o Credit Debit Operations List 1. Store Keys 3 4 3 5 2. Store remaining attributes 3. Gain Transaction 4. Replace Balance using Balance + Credit Amount 5. Replace Balance using Balance - Debit Amount 6. Store Date Closed
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