Derick Mussen Preventive Healthcare

Hierarchical Database System

• Wish you could decide if your having a boy or a girl?
• The Ebook To Cure Multiple Sclerosis
• The Secret to Overcoming Anxiety, Panic And Worry

A hierarchical database system is the simplest type of database system. In systems of this type the various data types (entities) are systematically assigned to various levels (Figure 2). The hierarchical system is represented as an upside-down tree with one root segment and ordered nodes. Each parent object can have one or more children (objects), but each child has only one parent. If an object has more than one parent the entity has to be duplicated in another place in the database hierarchy.

In order to trace (find, change, add, or delete) a segment in the database, the sequence in which the data are read is important. Thus, the sequence of the hierarchical path is: parent > child > siblings. The assignment of the data entities uses pointers. In our example, the hierarchical path to K is traced in Figure 2.

Typical examples of hierarchical database systems are the file systems used in personal computers. In the domain of chemistry, the in-house compound and reaction database systems MACCS (Molecule Access System) and REACCS (Reaction Access System) were hierarchical database systems, as was the first version of its successor, ISIS.

The primary advantage of hierarchical databases is that the relationship between the data at different levels is simple. This simplicity and efficiency of the data model is a great advantage of the hierarchical DBS (e.g., IMS: Information Management System by IBM). Large data sets, such as a series of measurements where the data values are dependent on different parameters such as boiling point, temperature, or pressure, can be implemented with an acceptable response time.

The disadvantage of hierarchical databases is that the implementation and management of the database requires a good knowledge of the organization (physical level) of the data storage. In addition, it is difficult to administer the structure of the database, as new relations or nodes result in a complex system of management tasks. Therefore, a modification of the logical data-independent data structure in a DBS of this type, which has limited flexibility, may demand significant modifications to the application programs. Furthermore, the hierarchical model suffers from the problem that a child cannot be related to multiple parents, and from the redundancies necessary to remedy this.

Figure 2 Hierarchical structure of a database. For example, object E in level 2 is the parent of the child objects J and K. The red arrows indicate the hierarchical path to trace the sequence to object K.