"Why has the relational data model become the most common model?"
If this sounds like an essay question for a homework assignment, you right!
Hi there,
There are several reasons why the relational data model has become the
most common one for use in databases, the main one being that it is
demonstrably superior in many respects to the previous data models
that were employed in database construction. It is also widely
acknowledged and understood to be so.
To understand why the relational model has largely supplanted previous
models it is necessary to briefly look at what the previous models
were, and the problems that they had that the relational model
addressed.
For starters, previous databases were flat. This means that the
information was stored in one big text file, often called a tab
delimited file. Each entry in the tab delimited file was separated by
a special character, such as a vertical bar (). Each entry contained
multiple pieces of information (fields) about a particular object or
person grouped together as a record.
This text file format made it difficult to search for specific
information or to create reports that included only certain fields
from each record. You would, for example, have to search sequentially
through an entire database of employee information to generate a
report about their salaries (assuming that 'salary' was an information
field that all the employee records in question contained).
Along with other previously employed models such as 'hierarchical' and
'network' models, the basic problem with flat databases was that
people working with one had to have an understanding of how the data
was structured within it in order to retrieve, insert, update, or
delete records from the database.
In 1970, when E.F. Codd developed the relational database model, it
could be seen to be a great improvement over previous models. At the
core of the then-new relational model was the concept of a table (also
called a relation) in which all data is stored. Each table is made up
of records (horizontal rows also known as tuples) and fields (vertical
columns also known as attributes). It is important to note that how or
where the tables of data are stored made no difference. Each table
could be identified by a unique name and that name could be used by
the database to find the table behind the scenes. As a user, all you
had to know was the table name in order to use it. You would not need
to worry as you did previously about the complexities of how the data
is stored on the hard drive.
The structure of a relational database also allowed sorting based on
any field and the generation of reports that contain only certain
fields from each record. A relational database uses the relationship
of similar data to increase the speed and versatility of the database.
This data access methodology made the relational model a lot different
from and better than the earlier database models because it was a much
simpler model to understand and work with. This is another
widely-cited reason for the popularity of relational database systems
in the world today.
In addition to being relatively easy to create and access, a
relational database also had the important advantage of being easy to
extend. After the original database creation, a new data category
could be added without requiring that all existing applications be
modified (such as would normally be required with flat file databases,
for example).
Another benefit of the relational system is that it provided extremely
useful tools for database administration. Essentially, tables can not
only store actual data but they can also be used as the means for
generating meta-data (data about the table and field names which form
the database structure, access rights to the database, integrity and
data validation rules etc).
Lastly, along with the development of the relational data model came
the development of SQL (Structured Query Language, a database query
language). SQL is relatively easy to learn, has been adopted as an
industry-wide standard since 1986, and allows people to quickly
develop the capability to query and modify a relational database. The
straightforwardness and simplicity of manipulation that SQL permits is
another part of the reason that relational databases now form the
majority of databases to be found.
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additional clarification from me if you do not feel this response
adequately answers your query.
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Regards,
-dakur-ga Knowing Just Enough about Relational Databases - For Dummies::
Building a system in Oracle or some other relational database product does not automatically make it a relational database. Similarly, you can design a
http://www.dummies.com/WileyCDA/DummiesArticle/Knowing-Just-Enough-about-Relational-Databases.id-4161.htmlHOME |
... because it is the logical thing to do?
Databases (in dBaseIII+ sense) somehow need to cross reference other
datas, and the only correct way to do it is by using Relations.
It is just common sense. If one database hold your name, ssn/id,
address, then another database about your speeding tickets would be
better not to duplicate those same information. Thus, Relational
Database.. :)
1. Logical structure of the data is separate from the physical data
(bits and bytes).
2. The logical structure of the data does not depend on relationship
between rows. A query specifies a set of rows based on their
attributes. This eliminates the frequent situation where the physical
sort order of data determines the results -- i.e. you get the same
result, regardless of the (sort) order of the rows. A big deal.
Main advantages of a relational database against a flat file system.
If you have a flat file system listing orders from various customers
for your products. The details of each product and customer has to be
entered for each record in the table.
However this could be normalised in a Relational Database, with one
table for products, one table for customers and one table for orders.
For each order instead of typing in all the information you simply
type in a Product ID and Customer ID which references the other two
tables.
The advantages of this are.
- Less time spent inputting data reduced.
- No chance of discrepencys between data (E.g. A Customer cannot have
be accidentally be given two addresses as a result of a typo).
- Less memory is required (As data is only stored once).
- All entries can be updated by changing just one record.
Hope that helps.
Mike Edgington Relational Databases Content on InfoQ::
Relational Databases Content on InfoQ. Latest featured content about Relational Databases Continuous Integration And Version Control for Databases
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Relational Database Integration with RDF/OWL::
Jul 29, 2008 Using the W3C OWL ontology standard lets you get more out of all kinds of data. Find out how this standard and some free software lets you
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Also, check your textbook - questions like these usually can be
answered by pasting the first and last paragraphs (or so) from the
chapter that they are covered it.
This question is in reference to databases, not programming. Sorry for
the vaqueness.
Is the question referring to databases or object modeling for programming?
Makes a bit of a difference.
Very detailed and thought out answer.
Thanks!
 Where was the last debate on wednesday with Mccain and Obama?
 INSTANCE / WAITING FOR SPRING
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Relational Databases