Providing Access to External Databases - High-Performance Web Databases: Design, Development, and Deployment - page 488

Thus, the database manager must consider the update frequency when
considering using a particular database access method.
DATABASE ACCESS COST
Determining the type of external information that must be accessed
involves considering alternative information providers. The database man-
ager should review the information provided by external database ven-
dors, along with their access or subscription fees, to determine the cost
associated with each database. The one-time cost associated with any
required hardware must also be considered; for example, the cost associ-
ated with a subscription to a database provided on CD-ROM disks includes
the cost of a CD-ROM reader if one is not currently available. Similarly, if an
employee requires access to a dial-in information access provider and does
not have a modem, the cost of the modem should be considered.
ECONOMIZING ON MULTIPLE ACCESS REQUIREMENTS
The database manager can consider several techniques when more than
one employee needs access to an external database. A local area network
(LAN) can provide shared access to transmission and data storage facili-
ties. The manager can negotiate usage-based contracts that reduce the
cost of database access as access increases. Because many organizations
have LANs, this chapter focuses on LAN solutions.
The first method to consider is accessing an external database over the
switched telephone network. The conventional method for providing this
access is to install a separate telephone line and modem for each user
requiring use of the switched telephone network. Doing so can result in a
one-time cost of $100 to $500for a modem and appropriate communica-
tions software, as well as a monthly business line telephone charge of $50
or more, not including the cost of long-distance charges.
Companies that have LANs can handle their various uses for the
switched telephone network by connecting an asynchronous communica-
tions server to a group of modems called a modem pool. Exhibit 2 illus-
trates an Ethernet bus-based LAN in which each network user can access
a modem from a five-modem modem pool. A workstation user can use any
available modem and the business line that connects it to the switched
telephone network.
The cost of an asynchronous communications server, including required
hardware and software, is approximately $3,000 for a Novell NetWare-based
network. Assuming the cost of each modem is$300, the total hardware and
software cost to establish a five-modem modem pool is approximately $400.
Assuming each business telephone line costs $50 per month, the monthly
cost for the modem pool illustrated in Exhibit 2 is $250. If modems cost