Database design involves identifying relationships between data and mapping them in an organized way. There are three types of design: conceptual, logical, and physical. Conceptual design identifies entities and relationships, while logical design brings order to relationships. Physical design results in a functional database.
Database design involves identifying the relationships that exist between separate pieces of data and mapping those relationships in an organized way that makes sense. There are different types of database design: conceptual database design, logical database design, and physical database design. The logical and physical design of the database is perhaps the simplest. The conceptual design of the database is a little more ambiguous because there is no direct work on a database model during this phase. The process is purely an exercise in identifying relevant data.
Two main things that are identified in conceptual database design are entities and relationships: Entities are actual objects in the material world, and relationships are the network of connections that connect one entity to another indefinitely. Hence the central notion of this type of design: the entity-relationship model. This lacks the general organization and structure that will be inherent in logical database design; it is, however, a precursor to it.
Relationship cardinalities are an essential part of the entity relationship model used in conceptual database design. Cardinalities express the frequency with which an entity experiences a particular relationship with another entity. In the current model these are indicated by the points where an entity on the diagram branches off to connect with single or multiple entities. Various “attributes” such as names, qualities and quantities associated with entities and relationships are also represented in the model.
Final considerations in developing an entity relationship model for conceptual database design include assigning each observed attribute to a particular domain and double-checking to ensure that everything in the model makes sense. Checking all involves finding and filtering all repeating data, ensuring that all attributes are associated with the correct entities and relationships, and confirming that all associations in the diagram are logical. If the connections aren’t logical in a real-world context, they must be at least abstractly logical.
The logical design of the database follows the conceptual stage. The process brings order and coherence to those previously mapped relationships and organizes them in such a way that they can actually be used for physical database design. Completion of tasks in physical database design results in a functional and well-structured database in light of work done in conceptual database design and logical database design.
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