Entity–attribute–value model (EAV) is a data model to describe entities where the number of attributes (properties, parameters) that can be used to describe them is potentially vast, but the number that will actually apply to a given entity is relatively modest. In mathematics, this model is known as a sparse matrix. EAV is also known as object–attribute–value model, vertical database model and open schema.
You will typically use an EAV pattern when you have Entities with a variable number of attributes, and these attributes can be of different types. This makes it impossible to define these attributes as column in the entity’s table, because there would be too many, most of them will not have data, and you can’t deal with dynamic attributes at all because columns need to be pre-defined in relational databases.
To solve this situation in a relational fashion you would create a child table, and relate that to the ‘entity’ table using a One-to-Many relation, where every attribute would become a record in the child table (“eav_attributes” in the image). Downside of this approach however is that to be able to get a specific attribute value, you’ll have to loop over all related records, compare the value of the attribute column with the attribute you look for, and if a match is found, get the contents of the value column.
QuickAppsCMS’s EAV API uses this same implementation, but allows you to merge these virtual attributes with the entity, so the attributes become properties of the entity object.