Advantages of hierarchical databases

A hierarchical database model consists of data arranged into a structure that looks a lot like a family tree or company organizational chart. If you need to manage data that lends itself to being represented as parent/child relationships, you can make use of the hierarchical database model. Suppose, for example, that you have a home food delivery service and need to know how much of each grocery item you have to purchase in order to fill your customer orders for a particular delivery date. In a hierarchical database, each parent record can have multiple child records; however, each child must have one and only one parent.

The main advantages of the hierarchical database are:

• Performance. Navigating among the records in a hierarchical database is very fast because the parent/child relationships are implemented with pointers from one data record to another. The same is true for the sideways relationships from child to child and parent to parent. Thus, after finding the first record, the program does not have to search an index (or do a table scan) to find the next record. Instead, the application needs only to follow one of the multiple child record pointers, the single sibling record pointer, or the single parent record pointer to get to the "next" record.

• Ease of understanding. The organization of the database parallels a corporate organization chart or family tree. As such, it has a familiar "feel" to even nonprogrammers. Moreover, it easily depicts relationships where A is a part of B (as was the case with the order database we discussed, where each item was a part of an order).

The main disadvantage of the hierarchical database is its rigid structure. If you want to add a field to a table, the database management system must create a new table for the larger records. Unlike an SQL database, the hierarchical model has no ALTER TABLE command. Moreover, if you want to add a new relationship, you will have to build a new and possibly redundant database structure.

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