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Database Model
There are different types of database management systems, each is characterized by the way in which data are defined and structured of the database. The database model defines the manner in which the various files of a database are linked together. There are mainly four types of database models commonly used. They are:
- Relational Database Model (RDBM)
- Hierarchical Database Model (HDBM)
- Network Database Model (NDBM)
- Object-Oriented Database Model (OODBM)
- Entity Relational Data Model (ERDM)
Relational database model
A database model in which the data elements are organized in the form of multiple tables and the data in one table is related to the data in another table through the use of a common field. It is a digital database whose organization is based on the relational model of data, as proposed by E. F. Codd in 1970. The various software systems used to maintain relational databases are known as relational database management systems (RDBMS).
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| Fig. Relational Database Model |
In the fig, the table of student info is related to the subject through the sid.
Advantages: Relational Database Model
- It has less redundancy because of the primary key.
- Normalization of the database is possible.
- Rapid database process.
- Easy for searching of data.
- Referential integrity can be applied.
Disadvantages: Relational database model
- It is complex to maintain than others.
- We have to apply many rules.
- It is not user-friendly.
The difference between DBMS and RDBMS are:
| Database Management System | Relational Database Management System |
| It allows storing data in a single table. | It allows storing data in multiple tables. |
| It does not allow setting relationships. | It allows setting relationships among tables. |
| It allows a single user to access information. | It allows multiple users to access information simultaneously. |
| Example dBase, Fox base, etc. | Example MS-Access, Oracle, etc. |
Hierarchical Database Model
In the hierarchical database, the data elements are linked in the form of an inverted tree structure with the root as the top and the branch formed below. below the single-root data element are subordinate elements, each of which in turn, has one or more other elements. There is a parent-child relationship among the data elements of a hierarchical database. A parent data element is one or more subordinate data elements. The data elements are below a parent are its children data elements.
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| Fig. Hierarchical Database Model |
Advantages: Hierarchical Database Model
- Searching is fast and easy if a parent is known.
- It is the easiest model than other database models.
- Very efficient in handling ‘one to many’ relationships.
Disadvantages: Hierarchical Database Model
- It is an old model of the database.
- Difficult to modification and addition of a child.
- It can’t handle ‘many-to-many’ relationships.
Network Database Model
A network database structure is an extension of the hierarchical database structure. In this model, the data elements of a database are organized in the form of parent-child relationships and all types of relationships among the data elements must be determined when the data is the first design. In-network database model a child data element can have more than one parent or no parent at all. In this model the database management system permits the extraction of the needed information by beginning from any data elements in the database structure instead of starting from the root data element.
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| Fig. Network Database Model |
In the above figure, the data has more than one parent but the data ram has no parents.
Advantages: Network Database Model
- It has more flexibility.
- It reduces data redundancy.
- Searching is fast because of the multi-directional pointer.
- It accepts many-to-many relationships.
Disadvantages: Network Database Model
- Difficult to sort data.
- The very complex type of database model.
- Need long programs for relationships.
Object-Oriented Database Model
The object-oriented database model was introduced to overcome the disadvantage of other database models. This database model is a logical organization of the real-world objects (entities), constraints on them, and relations among them. A database model that captures object-oriented concepts such as class hierarchy, inheritance, and method is an object-oriented database model. An object-oriented database model is a collection of objects whose behavior and state, and relationship are defined in accordance with an object-oriented database model. An object-oriented database management system is one that allows the definition and manipulation of an object-oriented database.
For example, the object-oriented database is shown in fig below;
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| Fig. Object-Oriented Database Model |
In the example above the vehicle is the root of the class-composition hierarchy, which includes the class vehicle spec, two-wheelers, and four-wheelers.
