Database development?

Question

What point in the development model is it important to know that the database will be managed by a relational DBMS? what is the reason?

The Model of database development can be found in
Pg13, the right figure :
http://home.netvigator.com/~angbil/handout3.ppt

Answer 1

Relational database makes the design simple and easy to retrieve data
so we follow these models

Answer 2

The most popular definition of an RDBMS is a product that presents a view of data as a collection of rows and columns not based strictly upon relational theory. The majority of real world popular RDBMS products implement some of Codd's 12 rules.

A second, theory-based school of thought argues that if a database does not implement all of Codd's rules (or the current understanding on the relational model, as expressed by Christopher J Date, Hugh Darwen and others), it is not relational. This view, shared by many theorists and other strict adherents to Codd's principles, would disqualify most DBMSs as not relational. For clarification, they often refer to RDBMSs as Truly-Relational Database Management Systems (TRDBMS), naming others Pseudo-Relational Database Management Systems (PRDBMS).

Almost all DBMSes employ SQL as their query language. Alternative query languages have been proposed and implemented, but very few have become commercial products.

Strictly speaking, a relational database is merely a collection of relations (frequently called tables). Other items are frequently considered part of the database, as they help to organize and structure the data, in addition to forcing the database to conform to a set of requirements.

Then there are the element s to be defined to RDBMS are:
Relations or tables
Constraints
Data domain
Keys
Foreign keys
Transition constraints
Relvars
Stored procedures
Indices
Relational operations

Normalization
Normalization is a process of altering the structure of the database to make the database conform to one or more best practices, to assist in performance and ease of data manipulation. The most common forms of normalization applied to databases are called the normal forms.