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ELH 1 Entity Life Histories Model the system from the viewpoint of how information is changed. – Diagrammatic representation of the life of an entity from.

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Presentation on theme: "ELH 1 Entity Life Histories Model the system from the viewpoint of how information is changed. – Diagrammatic representation of the life of an entity from."— Presentation transcript:

1 ELH 1 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)

2 ELH 2 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 Account opened Cash Deposit£2000 Cheque Cashed£20 Direct Deposit£1000 Cheque Cashed£20 Direct Deposit£2000 P. Penniless Account Account Opened Pay deposit£500 Cheque Cashed£200 Cheque Cashed£300 Cheque Cashed£300

3 ELH 3 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 Account Life Account Deletion Bank Account Closure Account Opened Credit Debit Balance Change * o o

4 ELH 4 EVENT Something that triggers a process to update system data May have an effect on several entities Matrix shows effects of events on entities Account Opened Credit Debit Account Closure Customer Bank Account Transaction Events Entities C M C M Effect of event on entity is: Creation C Modification M Deletion D Account Deletion D

5 ELH 5 ELH Notation Account Life Account Deletion Bank Account Closure Account Opened CreditDebit Balance Change * NodesEvents having an Effect on the Entity Entity name o o

6 ELH 6 Sequence '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 A B C D Entity X

7 ELH 7 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 Selection A B C D EF G Entity X o o o

8 ELH 8 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 EFG A o oo o

9 ELH 9 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! Iteration A B C D EF G H * Entity X ooo

10 ELH 10 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

11 ELH 11 Parallel Structures Event 'N' may affect the entity a number of times during the sequence of K, L and M. Node 'I', representing the sequence, and the node 'J', representing the iteration, are shown under the parallel bar Entity X DA BC F G H I J K L M N * * E o oo

12 ELH 12 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 ** ** AB J KJLJM J D NN N N HG F E * oo o

13 ELH 13 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 Possible event sequences are: abcbcde, ade, abe, abcbe Known as a disciplined conditional quit Y A1DE 2 CB R1 Q1 *

14 ELH 14 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 Illegal in SSADM Entity X EF JI HG NMLK ABDC * ooo*

15 ELH 15 Equivalent Diagram to SSADM Standards Two new nodes, P and Q, ensure that each parent node has children of only one type. J I KLMN F E G H Entity X B C D A P * Q * o o o o

16 ELH 16 Random Quits and Backward Quits Quit backwards (reversion) to Account Life if Account Re-opened (Q1) Random Quit on Customer Death to Death Structure (R2) Account Life Bank Account Closure Account Opened Balance Change CreditDebit * Account Deletion Possible Re-open Account Re-opened Death Structure Customer Death Customer Deletion Q1 R2 R1 Q2: Quit from anywhere on Customer death to R2 o o o o

17 ELH 17 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 BA F4 2 C ED OO OO * * *

18 ELH 18 Corrected Version to SSADM Standards 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. X 3BA 21 65 F4C 7 ED o oo o * **

19 ELH 19 Effect Qualifiers (Optional Effects) Where one event can affect an entity occurrence in two or more ways Effect Qualifiers (shown in brackets) distinguish between two different effects of the same event (Debit) e.g. The event Debit will have different processing if account is overdrawn rather than in credit Account Life Account Deletion Bank Account Closure Account Opened Credit Debit Balance Change * Debit (account overdrawn) (account in Debit credit) Optional Effects

20 ELH 20 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] Account Life Account Deletion Bank Account Closure Account Opened Cheque or Cash Credit Transfer [New Account] Transfer [Closed Account] Final Withdrawal o ooo Entity Roles

21 ELH 21 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 Accoun t Opene d Account Life Account Closure Account Deletion Balance Change * Credit o Debit o Operations List 4. Replace Balance using Balance + Credit Amount 5. Replace Balance using Balance - Debit Amount 1. Store Keys 2. Store remaining attributes 3. Gain Transaction 6. Store Date Closed 3 43 5 12 6


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