What is the differences between conceptual and logical database design?

Lets see the definations and the conceptual and  logical versions of a single data model first then we'll see the comparision to understand the difference.

A conceptual data model identifies the highest-level relationships between the different entities.

Conceptual Model Design

A logical data model describes the data in as much detail as possible, without regard to how they will be physical implemented in the database.

Logical Model Design

Comparing the logical data model  with the conceptual data model diagram shown above, the main differences between the two:

• In a logical data model, primary keys are present, whereas in a conceptual data model, no primary key is present.
• In a logical data model, all attributes are specified within an entity. No attributes are specified in a conceptual data model.
• Relationships between entities are specified using primary keys and foreign keys in a logical data model. In a conceptual data model, the relationships are simply stated, not specified, so we simply know that two entities are related, but we do not specify what attributes are used for this relationship.

There is another physical level and here is its details .

Cheers!

First of all, thanks a lot Mr. Maalik for inviting me to answer this question.

Second: here is my answer which I found much more relevant from this site: http://www.1keydata.com/datawarehousing/conceptual-data-model.html

A conceptual data model identifies the highest-level relationships between the different entities. Features of conceptual data model include:

1. The important entities and the relationships among them.
2. No attribute is specified.
3. No primary key is specified.

A logical data model describes the data in as much detail as possible, without regard to how they will be physicaly implemented in the database.  Features of a logical data model include:

1. All entities and relationships among them.
2. All attributes for each entity are specified.
3. The primary key for each entity is specified.
4. Foreign keys (keys identifying the relationship between different entities) are specified.

Normalization occurs at this level.

Conceptual data model you worry just about the high level design. You recognize entities in your model, and relationships between them.

Logical model comes after conceptual when you explicitly define what are the table columns in each table.

I think that in the conceptual data model you worry mostly about the high level design (what your objects will be and how do they relate to each other).

The logical model comes after conceptual model is defined and it is when you explicitly define what the table structure will be, and the relationships between the tables

A conceptual database design helps you analyze the conceptual structure of an information system, to identify the principal entities to be represented, their attributes, and the relationships between them.

Another side, a logical database design helps you analyze the structure of an information system, independent of any specific physical database implementation.

For additional help, visit here: http://www.keenesystems.com/Services/DatabaseDesign.aspx