Database Reference
In-Depth Information
2.1.1 Flat Files Systems
Using a file system database model implies that no modeling techniques are applied and
that the database is stored in
flat files
in a file system, utilizing the structure of the operat-
ing system alone. The term “flat file” is a way of describing a simple text file, containing
no structure whatsoever—data is simply dumped in a file.
Any searching through flat files for data has to be explicitly programmed. The advantage
of the various database models is that they provide some of this programming for you.
For a file system database, data can be stored in individual files or multiple files. Similar
to searching through flat files, any relationships and validation between different flat files
would have to be programmed and likely be of limited capability.
Flat files are not databases at all. However, it is important to understand them for two reas-
ons. First, flat files are often used to store database information. In this case, the operat-
ing system is still unaware of the contents and structure of the files, but the DBMS has
metadata that allows it to translate between the flat files in the physical layer and the data-
base structures in the logical layer. Metadata, which literally means “data about data,” is
the term used for the information that the database stores in its catalog to describe the data
stored in the database and the relationships among the data. The metadata for a customer,
for example, might include a list of all the data items collected about the customer, along
with the length, minimum and maximum data values, and a brief description of each data
item. Second, flat files existed before databases, and the earliest database systems evolved
from flat file systems that preceded them.
Overall, the worst problem with the flat file approach is that the definition of the contents
of each file and the logic required to correlate the data from multiple flat files have to be
included in every application program that requires those files, thus adding to the expense
