- Hierarchical Database Model: – The hierarchical database model is an inverted tree-like structure. The tables of this model take on a child-parent relationship. Each child table has a single parent table, and each parent table can have multiple child tables. Child tables are completely dependent on parent tables; therefore, a child table can exist only if its parent table does. It follows that any entries in child tables can only exist where corresponding Parent entries exist in parent tables. The result of this structure is that the hierarchical database model supports one-to-many relationships.
- Network Database Model: – The network database model is essentially a refinement of the hierarchical database model. The network model allows child tables to have more than one parent, thus creating a networked-like table structure. Multiple parent tables for each child allows for many-to-many relationships, in addition to one-to-many relationships. there is a many-to-many relationship between employees and tasks. In other words, an employee can be assigned many tasks, and a task can be assigned to many different employees. Thus, many employees have many tasks, and vice versa
- Relational Database Model: – The relational database model improves on the restriction of a hierarchical structure, not completely abandoning the hierarchy of data. Any table can be accessed directly without having to access all parent objects. The trick is to know what to look for—if you want to find the address of a specific employee, you have to know which employee to look for, or you can simply examine all employees. You don’t have to search the entire hierarchy, from the company downward, to find a single employee. Another benefit of the relational database model is that any tables can be linked together, regardless of their hierarchical position. Obviously, there should be a sensible link between the two tables, but you are not restricted by a strict hierarchical structure; therefore, a table can be linked to both any number of parent tables and any number of child tables.
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