Flat-File Databases versus Relational Databases:
More than you will ever need to know
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A flat-file database consists of one table. A relational database comprises a
number of tables that are linked by foreign-key relationships.
In a flat-file database the same piece of information may be repeated lots
of times, for instance a flat-file database showing product sales may show a
product and its price each time a product is sold. That a product has a
particular price is really just one piece of information and a relational
database would only store it once, in a separate product table. The fact
that a flat-file database stores this information once for every time the
product is sold is an example of data redundancy. Data redundancy can
cause problems in a database system, for instance if a product's name
changes. In a flat-file database this change has to be made many times, but
in a relational database it only needs to be changed once.
Data redundancy can also lead to data inconsistency, for example if a new
row is created and the product's price is entered wrongly. In this case some
rows will give the product's price as one value and other rows will have a
different value. Relational databases avoid data consistency problems by
only storing each piece of information once. It is still possible to enter a
"wrong" price for a product, but it is impossible for the price to be
inconsistent if the database is designed properly.
Other problems associated with data redundancy are firstly the extra time it
takes for data entry (it takes time to write things out again and again) and
secondly the extra disk space that this requires.
Often a flat-file database will just be a CSV (comma-separated values) file.
In this case it is impossible to assign different levels of access to different
users. Even if the flat-file database is stored in a DBMS (database
management system) it is not possible to implement the table-level access
that relational databases allow.
A final, and rather complex disadvantage of flat-file databases is that the
user interface is dependent on the file structure. That means that if you
want to create a different view of the data, just some of the fields say,
then you have to create a new file. This is known as program-data
dependence. In a relational database the file structure is totally unrelated
to the table structure so it is possible to create all sorts of different views
of the data to suit different users.
Flat-file databases do have their advantages. Firstly, if the information is
printed out it is much easier to read for a human than would be a set of
relational tables.
Secondly, because flat-file database software does not need to do lots of
CPU-intensive look-ups to join a number of tables, queries can run much
faster than in relational databases. The process of splitting information into
separate tables so that there is absolutely no redundancy is called
"normalisation". In practice it is very rare for a relational database to be
fully normalised because of the effect this has on performance.
Advantages
Flat-file database
1. Fast data retrieval
2. Easier for a human
to read
Relational database
1. Less data
redundancy
2. Less data
inconsistency
3. Better security
4. Program-data
independence
Disadvantages
1. Duplicated data
2. Slower data entry
3. More disk space
required
4. Data inconsistency
is possible
5. Updates have to be
done multiple times
6. Little or no access
control
7. Program-data
dependence
1. Slower data
retrieval
2. Difficult to read
original table data