Logical Design In Datawearhouse

Logical Data Model (LDM) -

• A logical design is conceptual and abstract. The process of logical design involves arranging data into a series of logical relationships called entities and attributes.
• Logical data model includes all required entities, attributes, key groups, and relationships that represent business information and define business rules.
• An entity represents a chunk of information. In relational databases, an entity often maps to a table. An attribute is a component of an entity and helps define the uniqueness of the entity. In relational databases, an attribute maps to a column.

Logical design  in Data wearhouse

Important Terms:

Entity

•      Entity: Are the principal data object about which information is to be collected. A class of persons, places, objects, events, or concepts about which we need to capture and store data.

1.      Persons:  agency, contractor, customer, department, division, employee,       instructor, student, supplier.
2.       Places:  sales region, building, room, branch office, campus. 
3.       Objects:  book, machine, part, product, raw material, software license,  software package, tool, vehicle model, vehicle.  
4.       Events:  application, award, cancellation, class, flight, invoice, order, registration, renewal, requisition, reservation, sale, trip.
5.       Concepts:  account, block of time, bond, course, fund, qualification, stock.
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•      Relationship:A natural business association that exists between one or more entities. The relationship may represent an event that links the entities or merely a logical affinity that exists between the entities

Relationship

         An example of a relationship would be:

1. Employees are assigned to projects.
2. Student enrolling in a curriculum.
3. Projects have subtasks.
4. Departments manage one or more projects 

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•      Cardinality:The cardinality of a relationship is the actual number of related occurrences for each of the two entities. The basic types of connectivity for relations are: one-to-one, one-to-many, and many-to-many. The minimum and maximum number of occurrences of one entity that may be related to a single occurrence of the other entity. Because all relationships are bidirectional, cardinality must be defined in both directions for every relationship.

Cardinality

•     Cardinality Notations:

       

    

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