Logical Models › How to Construct a Logical Model

How to Construct a Logical Model

The first step in constructing a logical model is developing the Entity Relationship Diagram (ERD), a high-level data model of a wide business area. An ERD is made up of three main building blocks: entities, attributes, and relationships. If you view a diagram as a graphical language for expressing statements about your business, entities are the nouns, attributes are the adjectives or modifiers, and relationships are the verbs. Building a data model is simply a matter of putting together the right collection of nouns, verbs, and adjectives.

The objective of the ERD is to provide a broad view of business information requirements sufficient to plan for development of the business information system. These models are not very detailed (only major entities are included) and there is not much detail, if any, about attributes. Many-to-many (non-specific) relationships are allowed and keys are generally not included. This is primarily a presentation or discussion model.

An ERD may be divided into subject areas, which are used to define business views or specific areas of interest to individual business functions. Subject areas help reduce larger models into smaller, more manageable subsets of entities that can be more easily defined and maintained.

There are many methods available for developing the ERD. These range from formal modeling sessions to individual interviews with business managers who have responsibility for wide areas.