Developing a Conceptual Model › Identifying Entities and Attributes › Step 1: Identifying Primary Entities

Step 1: Identifying Primary Entities

The first task in building your conceptual data model is to review the data items from your analysis of business information. Determine which are the most pertinent items and group them into primary entities.

To determine primary entities, select the objects that are important to your business. The end users of your application can be a good source to help you identify primary entities. They know what the entities are for their particular business because they physically handle them everyday.

Customers place orders for products on order entry forms. The company sells products. Your application needs data to process an order entry form to meet the business requirements. The following example shows a typical Order Entry form.

ABC Company                                           Customer Copy

Customer Code:

                                                     Phone:

Name

Address                                               Order Number

                                                    Date

Product Code          Description     Qty             Price           Total

___________            ___________      ___              _____           ______

___________            ___________      ___              _____           ______

___________            ___________      ___              _____           ______

___________            ___________      ___              _____           ______

For this Order Entry application, you would consider the following primary entities. They are represented as independent boxes:

The entities you have just selected (Customer, Company, Order, and Product) represent information that is pertinent to this kind of business.

However, you realize there will be situations when some products being ordered may be out of stock. Those particular products must be put on purchase orders, which will be placed with specific vendors or suppliers who supply them to the company. Each vendor or supplier supplies a particular type of product, and you want to be able to distinguish between products.

You now want to add more entities to represent your requirements:

Note: Entities should be given precise and concrete names. For example, use Customer instead of Person, or Country instead of Place. Use singular instead of plural form, such as Customer, not Customers.

You have identified and listed some entities you think are important to represent and describe the information needed for your business application. At this point, the list of entities you produced is the first version of your data model.

Your entities should be constantly re-evaluated, reorganized, and redefined to ensure that they are really what you meant them to be, and that they can be used as you intended.