What elements comprise a database? This article deals mainly with the objects that comprise a database. Several concepts are worthy of coverage within the scope of the database as it relates to database design. As you work with data and databases, you will see how the origination of business information and databases is formulated into database elements. The intent here is to provide a brief coverage of basic database elements to provide you with a basic understanding of the elements found in a database.
Several topics are discussed in the following sections. These topics include:
The database schema
Schema objects
Indexes
Tables
Fields and columns
Records and rows
Keys
Relationships
Data types
Database Schema
A schema is quite simply a group of related objects in a database. Within a schema, objects that are related have relationships to one another, as discussed earlier. There is one owner of a schema, who has access to manipulate the structure of any object in the schema. A schema does not represent a person, although the schema is associated with a user account that resides in the database.
The three models associated with a schema are as follows:
The conceptual model, also called the logical model, is the basic database model, which deals with organizational structures that are used to define database structures such as tables and constraints.
The internal model, also called the physical model, deals with the physical storage of the database, as well as access to the data, such as through data storage in tables and the use of indexes to expedite data access. The internal model separates the physical requirements of the hardware and the operating system from the data model.
The external model, or application interface, deals with methods through which users may access the schema, such as through the use of a data input form. The external model allows relationships to be created between the user application and the data model. Figure 1 depicts a schema in a relational database.