Database definitions

I am going to start a database and need to know the difference between
Data Modeling, Schema and Database design?

I always thought of Data Modeling and schema as defining relationships
and primary and secondary key?


What is mean when someone designs an E-R diagram and a Data Flow
Diagram??

Data Modeling is the process of creating a description of the
relationships between data elements of interest.  When data modeling
for relational databases, your description usually identifies tables,
columns, and foreign key relationships.  The "description" usually
involves pictorial representation, e.g., boxes and arrows.

A logical data model is sometimes developed before the physical model.
The logical model is perhaps not as normalized as the physical, and
usually does not describe indexes or other performance-related
considerations.  This model is most useful for communicating with
non-dba's who are interested in the data content of a system but don't
care about the physical storage considerations.

A physical data model more closely resembles the way that the data will
be actually stored in the db.  It may specify indexes.

A Entity-Relationship diagram is the most common pictorial
representation of a data model, logical or physical.  It's just a way
of showing the model with boxes and arrows and some special symbols
(e.g., 0..1 or 0..n) .  A picture is worth a thousand words.

The schema is the actually definition of the data model in the dbms.
When you take your data model and start creating tables, columns,
indexes, and fkeys, you are creating the schema.

Of course, the data model is a representation of the schema that you
intend to create, so the terms are sometimes used interchangably.  As
you show the data model to someone, you might say "here's the schema
design" or you might just shorten that to say "here's the schema".  Not
quite correct, but good enough.

So, in summary, Data Modeling is an activity that results in a Data
Model.  An ERD is one way of representing a data model.  The data model
is used to create the databases's schema.


A data flow diagram is something entirely different.  It is a pictorial
representation of how data is transformed as it moves through
processing steps of an application.  For example, a data flow diagram
may show a authorization for a credit purchase as input.  In an early
processing step, it will be matched against a database of account
holders.  Then  the purchase amount will be compared to the balance.
etc.

Hope this helps.

THANKS!!
lit@twcny.rr.com  wrote:
> Data Modeling is the process of creating a description of the
> relationships between data elements of interest.  When data modeling
> for relational databases, your description usually identifies tables,
> columns, and foreign key relationships.  The "description" usually
> involves pictorial representation, e.g., boxes and arrows.
>
> A logical data model is sometimes developed before the physical
model.
> The logical model is perhaps not as normalized as the physical, and
> usually does not describe indexes or other performance-related
> considerations.  This model is most useful for communicating with
> non-dba's who are interested in the data content of a system but
 don't

> care about the physical storage considerations.
>
> A physical data model more closely resembles the way that the data
will
> be actually stored in the db.  It may specify indexes.
>
> A Entity-Relationship diagram is the most common pictorial
> representation of a data model, logical or physical.  It's just a way
> of showing the model with boxes and arrows and some special symbols
> (e.g., 0..1 or 0..n) .  A picture is worth a thousand words.
>
> The schema is the actually definition of the data model in the dbms.
> When you take your data model and start creating tables, columns,
> indexes, and fkeys, you are creating the schema.
>
> Of course, the data model is a representation of the schema that you
> intend to create, so the terms are sometimes used interchangably.  As
> you show the data model to someone, you might say "here's the schema
> design" or you might just shorten that to say "here's the schema".
Not
> quite correct, but good enough.
>
> So, in summary, Data Modeling is an activity that results in a Data
> Model.  An ERD is one way of representing a data model.  The data
 model

> is used to create the databases's schema.
>
>
> A data flow diagram is something entirely different.  It is a
 pictorial
> representation of how data is transformed as it moves through
> processing steps of an application.  For example, a data flow diagram
> may show a authorization for a credit purchase as input.  In an early
> processing step, it will be matched against a database of account
> holders.  Then  the purchase amount will be compared to the balance.
> etc.
>
> Hope this helps.