Microsoft Office Tutorials and References
In Depth Information
DATABASE DESIGN
In Access, queries that answer a question are called select queries because they select relevant data from
the database records. Queries also can be designed to change data in records, add a record to the end of a
table, or delete entire records from a table. These queries are called update, append, and delete queries,
respectively.
Access has a report generator that can be used to format a table
s data or a query
s output.
DATABASE DESIGN
Designing a database involves determining which tables belong in the database and creating the fields that
belong in each table. This section begins with an introduction to key database design concepts, then
discusses design rules you should use when building a database. First, the following key concepts are defined:
￿
Entities
￿
Relationships
￿
Attributes
Database Design Concepts
Computer scientists have highly formalized ways of documenting a database
s logic, and learning their
notations and mechanics can be time-consuming and difficult. In fact, doing so usually takes a good portion
of a systems analysis and design course. This tutorial will teach you database design by emphasizing practical
business knowledge, and the approach should enable you to design serviceable databases quickly. Your
instructor may add more formal techniques.
A database models the logic of an organization
s operation, so your first task is to understand the
operation. You can talk to managers and workers, make your own observations, and look at business documents
such as sales records. Your goal is to identify the business
(sometimes called objects). An entity is
a thing or event that the database will contain. Every entity has characteristics, called attributes, and one or
more relationships to other entities. Take a closer look.
s
entities
Entities
As previously mentioned, an entity is a tangible thing or an event. The reason for identifying entities is that an
entity eventually becomes a table in the database. Entities that are things are easy to identify. For example,
consider a video store. The database for the video store would probably need to contain the names of DVDs and the
names of customers who rent them, so you would have one entity named Video and another named Customer.
In contrast, entities that are events can be more difficult to identify, probably because they are more
conceptual. However, events are real, and they are important. In the video store example, one event would be
Video Rental and another event would be Hours Worked by employees.
In general, your analysis of an organization
s operations is made easier when you realize that
organizations usually have physical entities such as these:
￿
Employees
￿
Customers
￿
Inventory (products or services)
￿
Suppliers
Thus, the database for most organizations would have a table for each of these entities. Your analysis also
can be made easier by knowing that organizations engage in transactions internally (within the company)
and externally (with the outside world). Such transactions are explained in an introductory accounting course,
but most people understand them from events that occur in daily life. Consider the following examples:
￿
Organizations generate revenue from sales or interest earned. Revenue-generating transactions
include event entities called Sales and Interest.
￿
Organizations incur expenses from paying hourly employees and purchasing materials from
suppliers. Hours Worked and Purchases are event entities in the databases of most organizations.
Thus, identifying entities is a matter of observing what happens in an organization. Your powers of
observation are aided by knowing what entities exist in the databases of most organizations.
 
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