Summary

Entity relationship modeling clarifies data content and relationships through the use of entities that contain attributes and are related to each other, tied by identity keys. After the model is defined, normalization rules are applied, which govern the design of the data model in an attempt to minimize data redundancy. Often, denormalization is then purposefully applied to add redundant data; this process improves system performance and reduces associated relationship overhead.

Primary keys are defined to provide a unique mechanism for referring to each row in a table, thus giving you quick access to records. Foreign keys are used in a table as a pointing mechanism to the primary key of another table for the purpose of establishing relationships between tables. Business rules coincide with the company's business goals. When you implement a database design, business rules and constraints help you maintain data integrity and focus the system design to meet business goals.

In the implementation of any database model, a balance between normalization and denormalization is required. Any model will undergo changes in design as the system progresses to implementation and will continue to evolve once in place. At the logical stage, the model is rarely a final design.

XML is a technology that encompasses data layout with validation against a schema. As another form of data, XML acts as a data source. As a more complete technology, it allows companies to share data and customize the data to the specific design they need.