Database Reference
In-Depth Information
The STUDENT
table—the key symbol
shows the primary key
The relationship between STUDENT and
GRADE—the number 1 and the infinity
symbol indicate that one student may be
linked to many grades by StudentNumber
Figure 1-4
Microsoft access 2013
View of tables and
relationships
Databases record facts and figures, so they record data. They do so, however, in a way that
enables them to produce information. The data in Figure 1-3 can be manipulated to produce
a student's GPA, the average GPA for a class, the average number of students in a class, and so
forth. In Chapter 2, you will be introduced to a language called Structured Query Language
(SQL) that you can use to produce information from database data.
To summarize, relational databases store data in tables, and they represent the relation-
ships among the rows of those tables. They do so in a way that facilitates the production of
information. We will discuss the relational database model in depth in Part 2 of this topic.
Database examples
Today, database technology is part of almost every information system. This fact is not
surprising when we consider that every information system needs to store data and the re-
lationships among those data. Still, the vast array of applications that use this technology is
staggering. Consider, for example, the applications listed in Figure 1-5.
Single-User Database applications
In Figure 1-5, the first application is used by a single salesperson to keep track of the customers
she has called and the contacts that she's had with them. Most salespeople do not build their
own contact manager applications; instead, they license products such as GoldMine (see
www.goldmine.com ) or ACT! (see http://na.sage.com/sage-act ) .
Multiuser Database applications
The next applications in Figure 1-5 are those that involve more than one user. The patient-
scheduling application, for example, may have 15 to 50 users. These users will be appointment
clerks, office administrators, nurses, dentists, doctors, and so forth. A database like this one
may have as many as 100,000 rows of data in perhaps 5 or 10 different tables.
When more than one user employs a database application, there is always the chance
that one user's work may interfere with another's. Two appointment clerks, for example, might
assign the same appointment to two different patients. Special concurrency-control mecha-
nisms are used to coordinate activity against the database to prevent such conflict. You will
learn about these mechanisms in Chapter 9.
The third row of Figure 1-5 shows an even larger database application. A customer
relationship management (CRM) system is an information system that manages customer
contacts from initial solicitation through acceptance, purchase, continuing purchase, support,
and so forth. CRM systems are used by salespeople, sales managers, customer service and sup-
port staff, and other personnel. A CRM database in a larger company might have 500 users and
10 million or more rows in perhaps 50 or more tables. According to Microsoft, in 2004, Verizon
had an SQL Server customer database that contained more than 15 terabytes of data. If that
data were published in topics, a bookshelf 450 miles long would be required to hold them.
Enterprise resource planning (ERP) is an information system that touches every de-
partment in a manufacturing company. It includes sales, inventory, production planning,
 
 
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