6.2 Elements and Relationships
Relationships have a direct impact on the elements within an entity. The Logical Modeler follows the rules of Chen E-R Data Models. Of particular importance are the following rules:
- An entity will obtain elements as the result of relationships with other entities.
- An element may be defined only once to a model.
- If an element exists in more than one entity, it must do so by means of a relationship.
For example, the Customer Code is an element of the Customer entity. The Order entity might also have a Customer Code element. Since Customer Code can be defined only once, the Customer Code in the Order entity must be the result of a join relationship with the Customer entity.
In the LANSA database files that are created, the names of the Customer Code fields will be based on the definition of the relationship between the two entities. For details about the field naming conventions for inherited elements, refer to 7.5 Relationships and Elements.
If you are not familiar with the rules of data modeling and how elements and relationships work together, you should attend the LANSA Modeling and Design Workshop. This guide does not teach the principles of data modeling.