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Chapter 2. The Basics of Database Design > Table Relationships - Pg. 33

The Basics of Database Design 33 The Vocabulary of Database Design The principles of database design have been written about extensively. Formal descriptions of relational da- tabases such as those you create in Microsoft Access include terms such as tuple, attribute, heading, and body --concepts that come from branches of mathematics. The term relation comes from the field of set theory and does not actually refer to the relationships between tables. A relation refers to the entire structure of a table. A tuple is the same as a record, and an attribute is the same as a field. Tables are often referred to as entities, and relationships are often referred to as constraints. A few other distinctions in terminology are important to keep in mind. Database experts often distinguish data from information. A piece of data is a raw fact; information is data that's been put in a context that makes it meaningful. For example, the number of units sold during a month is raw data, but a month-by-month com- parison showing sales trends is information. You'll also often see a distinction made between a database and a database application. A database consists of tables, and the database application consists of the forms and reports that people use to work with the data in the tables. Understanding these concepts is important when you're working with formal database design procedures. However, you can accomplish a lot in Access without having a comprehensive understanding of these terms, relying instead on the more familiar vocabulary that Access uses. Table Relationships The tables in a relational database can have different types of relationships. The three types are a one-to-one relationship, a one-to-many relationship, and a many-to-many relationship. In the sec- tions that follow, we'll demonstrate each type. To help, we'll modify the RelationshipDemo form by using another helpful wizard--the Command Button Wizard. This exercise will acquaint you with the sorts of actions you can assign to a command button using the wizard. Follow these steps. Use the Command Button Wizard 1. 2. 3. In the Database window, click Forms in the Objects list. Select the RelationshipDemo form, and then click Design on the Database window toolbar. In the toolbox, click the Control Wizards button so that it is enabled. This turns on wizards that you can use to create several types of controls. In the toolbox, click the command button icon, and then click in the form to add a button to the form. The Command Button Wizard starts, as shown here: