TYPES OF DATABASE STRUCTURE OR DATA MODELS
TYPES OF DATABASE STRUCTURE OR DATA MODELS
Generally, the database system is classified on the basis of one of the three data models, they use in building the conceptual structure or schema of the database. The three models are:
1. Hierarchical model
2. Network model, and
3. Relational model
Hierarchical model: in the hierarchical structure, the relationships between records are stored in the form of a hierarchy or a tree which has a root. In this model, all records are dependent and arranged in a multiline structure, thus the root may have a number of branches and each branch may have a number of sub-branches and so on. The lowermost record is known as the ‘child’ of the next higher level record, whereas the higher level record is called the ‘parent’ of its child records. Thus in this approach, all the relationships among records are one-to-many. The hierarchical database model (HDBM) is applicable when the data in an organization can be put down in the hierarchical or in terms of the levels, one after another. The data model is equivalent to the tree. A tree has roots, branches, and leaves; their equivalent s in the HDBM beings records, notes, and field. In the HDBM the data is stored in the hierarchical form recognizing the fact that each of the levels is bounded by the parent-child relations to the earlier level. The typical characteristics of HDBM are:
HDBM starts with a root and has several roots
The root will have several branches
Each branch is connected to one and only one root
A branch has several leaves and a set of leaves are connected to one branch
Network database model: the NDBM interconnects the entities of an organization into a network. The NDBM deals with the set of the components of the record, apart, a subassembly and an assembly are the records. A record located at the tail of the arrow is known as a member record at the head of the arrow is known as an owner. An arrow connecting the owner to a member is a set.
Relational Database Model: in the RDBM, the concept of two-dimensional tables is used to show the relations. The relational model is currently more popular among users and developers because of the many interrelated tables, the overall design may get complicated which may lead to slower searches and thus affecting the access time.
