Understanding Database Model | Evolution of DBMS| Data models

 DBMS was first introduced during the 1960s and has continued to evolve during subsequent decades.

1960s : Traditional file system and first database management system were introduced.

1970s: Hierarchical and Network data base models also known as first generation DBMS

1980s: Relational model also known as second generation DBMS. in Relational model, all data are represented in the form of tables. A relatively simple fourth-generation language called SQL (Structured Query Language) is used for data retrieval.

1990s: Object-Oriented and Object-Relational data models.

DBMS   was developed to the limitations of file processing system.

Data models

        The structure of a database is called data model. this is used to describe the data and thier relationship among them. the following are the different types of data model.

1.         Hierarchical data model
2.         Relational data model
3.         network data model

Hierarchical data model

            This model represents database as a tree structure. in this data are organized as records and the records are stored from top to butoom as a tree. Each level of the tree or hierarchical structure contains a row of records. there is a parent child relationship among the various levels. the highest level record is named as root. The figure given below shows a hierarchical data model.

in the above example, the data are organized as records. Each record has a name and is stored in a tree structure.Each row containes a perticular types of record. for searching the detailes of an employee. the DBMS starts from the root and descends downwords.

Advantages

1.     simplicity

                    The design of hierarchical database is simple and the relationship between levels is logically simple.

      2.      Data integrity

                 since this model is based on parent child relationship, the child is always referenced to its parents. So this model provides data integrity.

       3.      Efficiency

            This model is more efficient when the database contains large number of one to many relationships..

Disadvantages  

1. The designer should have good knowledge in implementing this model.

2. Maintenance is very difficult.

3. Programming is very complex.

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