Sample IDEF1X Modeling Methodology

ERwin has been developed to support the IDEF1X and IE modeling standards, but is otherwise free from restrictions on any methodology. The use of various levels of models within the IDEF1X method, however, can be very helpful in developing a system. General model levels are outlined in the IDEF1X standard, and are presented below. In practice, you may find it useful to expand or contract the number of levels to fit individual situations.

The model levels generally trend from a very wide, but not too detailed view of the major entities that are important to a business, down to a level of precision required to represent the database design in terms understandable by a particular DBMS. At their very lowest level of detail, the models are said to be technology dependent, e.g., a model for an IMS database will look very different from a model for a DB2 database. At higher levels, the models are technology independent, and may even represent information which is not stored in any automated system.

The modeling levels presented below are well suited to a top-down system development life cycle approach, in which successive levels of detail are created during each project phase.

The highest level models come in two forms. The Entity Relationship Diagram (ERD) identifies major business entities and their relationships. The KeyBased (KB) Model sets the scope of the business information requirement (all entities are included) and begins to expose the detail.

The lower level models also come in two forms. The Fully Attributed (FA) Model is a third normal form model which contains all of the detail for a particular implementation effort. The Transformation Model (TM) represents a transformation of the relational model into a structure which is appropriate to the DBMS chosen for implementation.

The transformation model, in most cases, is no longer in third normal form. The structures have been optimized based on the capabilities of the DBMS, the data volumes, and the expected access patterns and rates against the data. In a sense, this is a picture of the eventual physical database design.

The database design is contained in the DBMS Model for the system. Depending on the level of integration of a business’ information systems, the DBMS Model may be a project level model, or an area level model for the entire integrated system.

14 ∙ Information Systems, Databases, and Models

These levels are presented in the figure below. Notice that the DBMS Model can be either at an “Area” scope, or a “Project” scope. It would not be uncommon to have single ERD and KB models for a business, and multiple DBMS Models, one for each implementation environment, and then another set within that environment for “projects” which do not share databases. In an ideal situation, there are a set of “Area” scope DBMS Models, one for each environment, with complete data sharing across all projects in that environment.

IDEF1X Database Design Levels

Information Systems, Databases, and Models ∙ 15