The hierarchical database model is one of the first database models to receive wide acceptance, primarily because of its ability to relate one section of data to another. In this model, which is tree-like in structure, there exist several levels of hierarchies that start with a parent node, and lead down to a child node. For example, if a parent node is “Name”, then the child node would be a list of names and the next level would be specific information about that name. While flexible when it first came out, the hierarchical database model is rarely used in modern databases, because modern databases have stronger relational grouping abilities.
In the hierarchical database model, everything is related to a hierarchy. There are a few overarching parent nodes on the top level of the database. When a user selects the node, a more specific node will appear and, when the user clicks one of those nodes, information that is even more specific will appear. For example, if the top hierarchy is “Exercise,” then the next nodes may be “Weight Lifting” and “Cardio,” and then there may be muscle groups for the former and running methods for the latter, and then even more specific information after that.
Created during the 1960s by IBM®, the hierarchical database model is considered the first database model ever deployed. In the early days of databases, this was considered extremely flexible, because database designers could easily show relationships between different nodes and users could easily input data. The hierarchical database became known as a one-to-many database, because one node related to many others.
When the relational database came out, the hierarchical database model lost popularity. This is because, compared to the relational database, the hierarchical database is inflexible. It can only relate one node to many others, while the relational model can relate several nodes to several other nodes. Newer versions of the hierarchical database allow designers to relate one parent node to several other nodes, but this is more difficult to program than the relational database.
While not in use for most modern databases, the hierarchical database model is still used for some applications as of 2011. For servers that are made to hold data for long periods without the data being touched, a hierarchical database is usually found, because that was the database model used when the server was created. Another reason to use the hierarchical model is that, when coupled with a simple database containing only a few records, it takes less time to program.