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WebSphere Application Server - IBM Redbooks

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2.5.3 Datatypes<br />

Datatypes is a column attribute definition used when creating tables. The<br />

datatype tells us what kind of data will be held in the column and what length it<br />

will be. Care should be taken when selecting datatype and size for a column to<br />

ensure that it can hold all possible values for that column and at the same time<br />

not be so large that it bloats the table and database size, thus adversely affecting<br />

performance.<br />

2.5.4 Deriving the data model from the use-case model<br />

As we saw in the requirements, the entities that interact with the Online Catalog<br />

sample are buyer and business owner. The buyer views and buys items. The<br />

business owner maintains the item inventory and pricing information.<br />

We came up with the following entities that map to the business requirements of<br />

the Online Catalog sample.<br />

► Customer: This entity contains all attributes/information about a buyer who<br />

buys from the online store.<br />

► Item: This entity contains all attributes/information about items on sale in the<br />

online store.<br />

► ShippingOrder: This entity contains all information needed to complete a<br />

shipping order.<br />

► Users: This entity contains the user name/password of all admin users.<br />

The data model of the tables required by the Online Catalog sample is shown in<br />

Figure 2-10 on page 40.<br />

Chapter 2. <strong>Application</strong> design 39

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