This chapter began with an explanation of why terminology is important for defining, discussing, or reading about the relational database model and the database-design process.
The section on value-related terms showed you that there is a distinct difference between data and information, and that understanding this difference is crucial to understanding the database-design process. You now know quite a bit about nulls and how they affect information you retrieve from the database.
Structure-related terms were covered next, and you learned that the core structures of every relational database are fields, records, and tables. You now know that views are virtual tables that are used, in part, to work with data from two or more tables simultaneously. We then looked at key fields, which are used to identify records uniquely within a table and to establish a relationship between a pair of tables. Finally, you learned the difference between a key field and an index.
Now you know that an index is strictly a software device used to optimize data processing.
In the section on relationship-related terms, you learned that a connection between a pair of tables is known as a relationship. A relationship is used to help ensure various aspects of data integrity, and it is the mechanism used by a view to draw data from multiple tables. You then learned about the three characteristics of table relationships: the type of relationship (one-to-one, one-to-many, many-to-many), the type of participation (optional or mandatory), and the degree of participation (minimum/maximum number of related records).
The chapter ended with a discussion of integrity-related terms. Here you learned that a field specification establishes the general, physical, and logical characteristics of a fieldcharacteristics that are an integral part of every field in the database. You then learned that data integrity is one of the most important aspects of the database-design process because of its positive effect on the data in the database. Also, you now know that there are four types of data integritythree based on database structure and one based on the way the organization interprets and uses its data. These levels of integrity ensure the quality of your database's design and the accuracy of the information you retrieve from it.