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Logical Data Modelling

Objectives. To provide a definition of the terms Logical Data Model (LDM) and Logical Data Structure (LDS)To explain what a LDS consists ofTo explain a step by step process by which a LDS can be constructed. . What is a Logical Data Model?. An abstract representation of the structural data require

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Logical Data Modelling

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    1. Logical Data Modelling

    2. Objectives To provide a definition of the terms Logical Data Model (LDM) and Logical Data Structure (LDS) To explain what a LDS consists of To explain a step by step process by which a LDS can be constructed

    3. What is a Logical Data Model? An abstract representation of the structural data requirements of part or all of an organisations operation

    4. What do Logical Data Structures Consist of ? Entity Types Relationship Types

    5. What is an Entity/Entity Type ? An Entity Type is a logical grouping of data relevant to the application in question An Entity is an Occurrence of an Entity Type An Entity Type would be represented in a RDBMS as a table. An Entity would be represented as a single row in a table

    6. Features of Entity Types An Entity Type can be a physical object, or an abstract concept or an event or anything else. It must be relevant. It must be identifiable. There must be the possibility of more than one occurrence.

    7. Soft Rectangles Containing the name of the Entity Type

    8. What is a Relationship Type ? A Relationship Type is a relevant business association between two Entity Types. A Relationship is an occurrence of a relationship type.

    9. One to One (1:1) One to Many (1:M) Many to Many (M:M)

    11. Recursive Relationships

    12. Resolving M:M Recursive Relationships

    13. Mutually Exclusive Relationships Exclusive Ownership Exclusive Membership

    14. Exclusive Ownership

    15. Exclusive Membership

    16. Types of 1:M Relationships Owner Optional : Member Mandatory Owner Mandatory : Member Mandatory Owner Optional : Member Optional Owner Mandatory : Member Optional

    17. A Customer may exist without placing any orders An Order must have been placed by one and only one Customer

    18. Owner Mandatory : Member Mandatory An Order must consist of at least one Order Line An Order Line must appear on one and only one Order

    19. Owner Optional : Member Optional A Employee may negotiate Orders if their job type is Salesperson An Order may be received directly from a customer and could thus exist independently of Employees

    20. Owner Mandatory : Member Optional A Commission Plan will only exist if at least one Employee is being paid via that plan An Employee who is not a Salesperson doesn’t get commission

    21. Entity/Event Modelling

    22. Objectives To explain the terms Entity/Event Model and Entity Life History To describe what ELHs consist of To introduce a step by step procedure for creating ELHs

    23. What is an Entity/Event Model? An Entity/Event Model is an abstract representation of how the entities in a system are affected by business events

    24. What do Entity Life Histories Consist of? Events Effects Structural Components

    25. What is an Event? A business event is a stimulus which causes a system to create, update or delete an occurrence of one or more entity types

    26. Types of Event External Events Internal Events Time Based Events

    27. What is an Effect? An effect is the change within a single entity, i.e. creation, update or deletion caused by an event Question:- Do ELHs show events or effects?

    28. Structural Components Sequence Selection Iteration Parallelism

    29. Sequence ‘A’ is a structural component which shows that effect ‘B’ is followed by effect ‘C’

    30. Selection ‘A’ is a structural component which shows that either effect ‘B’ takes place or effect ‘C’ but not both

    31. Iteration ‘A’ is a structural Component which shows that effect ‘B’ takes place 0 or more times

    32. Parallelism ‘A’ is a structural component which shows that either, both (in any order on any number of occasions) or neither of effects ‘D’ and ‘E’ may occur

    33. Complete Example

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