The relational database model exhibits the following structural characteristics:
A relational database contains multiple tables.
Each table stores data about one specific subject.
Fields contain data describing the subject of a table.
Records are particular instances of the subject of a table.
A specia primary key field uniquely identifies each record in a table.
The sample table below clarifies the structure of a relational database table.
The table exhibits the following characteristics:
The specific subject of the table is revealed in the title: Employees.
The fields describing employees are: LastName, FirstName, and HireDate.
The yellow highlighted row features the record of one employee: Sandy Reynolds.
The primary key uniquely identifying each record is EmpID.
In the next lesson, the structure of a relational database and its ability to be linked for accessing data will be discussed.
Why is Data Modeling Important?
Data modeling is probably the most labor intensive and time consuming part of the development process. Why bother especially if you are pressed for time? A common response by practitioners who write on the subject is that you should no more build a database without a model than you should build a house without blueprints. The goal of the data model is to make sure that the all data objects required by the database are completely and accurately represented. Because the data model uses easily
understood notations and natural language, it can be reviewed and verified as correct by the end-users.
The data model is also detailed enough to be used by the database developers to use as a "blueprint" for building the physical database. The information contained in the data model will be used to define the relational tables, primary and foreign keys, stored procedures, and triggers. A poorly designed database will require more time in the longterm. Without careful planning you may create a database that omits data required to create critical reports, produces results that are incorrect or inconsistent, and is unable to accommodate changes in the user's requirements.
RDBMS Structure - Exercise
Before moving on to the next lesson, click the Exercise link below to check your knowledge of the structure of a relational database table. RDBMS Structure - Exercise
primary key: A field (or combination of fields) that uniquely identifies a record in a table.