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Examples of file server, or desktop, databases are Access and Paradox. These
databases can be used in a multi-user networked environment, but there are
drawbacks.
All the processing during the operation of these databases is carried
out on the client's machine. The major drawback with this, is the amount
of network traffic that they generate. For instance, if you run a query
that says 'SELECT * FROM CUSTOMERS WHERE ID=356', your machine will have
to obtain all the records from 'CUSTOMERS', then process the query to
return only the record whose ID is 356.
The number of concurrent users is usually restricted to about twenty or
so. This is only a rule of thumb and the actual number can depend upon the
design of the system and the type of access required. Adding new or
editing existing records in the same table, will cause more restrictions
than simply viewing data, for example, via reports.
Security is not considered to be very tight. Although it can be pretty
good, it will not stop a knowledgeable or malicious hacker. It's OK in a
situation were its main purpose is to prevent accidental changes or
access, or were there is no requirement for extremely tight security.
Recovery and backups are simply whenever the file(s) containing the
data were last backed up. To restore a backup, you will have to overwrite
the existing file(s) and lose any data that was entered after the last
backup was taken. If the data exists in more than one file, it may be necessary
to restore all the files at the same time in order to maintain the
integrity of the data. However in a lot of situations, it is possible to
repair a corrupt file or table, without having to restore from a backup.
These databases perform
their processing on the server thus reducing network traffic. In the above
example, the query 'SELECT * FROM CUSTOMERS WHERE ID=356', would this time
only return the record whose ID = 356 across the network. Many of the
tasks that they perform, and the enforcing of business rules can be done through the use of stored procedures. They
can cope with thousands of users. However, they can still be subject
record locking problems. But they are designed to cope with them much
better. Security is much tighter. With SQL Server, NT security can be
used, so that groups of users can be defined using NT. This can do away
with the need to logon to the database separately. Instead, the NT logon
is used to obtain your access privileges. If all the data processes are
carried out through stored procedures, security can be implemented by
determining the levels of access to the stored procedures. Logs are kept
of all transactions and data can be recovered from to any point in time
using these logs.
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Access
Microsoft's market leader in desktop databases.
Paradox
Corel's popular database.
DBase
The original innovator for the genre.
Approach
A member of Lotus's SmartSuite.
SQL Server
Microsoft's server database for NT.
Oracle
The leading client-server database.
Informix
A high performance SQL database.
Interbase
Borland's SQL database.
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Access