User:Komal.Ar/Record based data models
A data model is a collection of concepts that can be used to describe the structure of a database. By structure of the database, we mean the data types, relationships, and constraints that should hold for the data.
Representational or implementation data models are the models used most frequently in traditional commercial DBMS's. These include the widely used relational model, as well as the network model and hierarchical data model. Representational data models represent data by using record structures and hence are sometimes called record-based data models.
The comparison between the three record-based data models are as follows :
| HIERARCHICAL DATA MODEL | NETWORK DATA MODEL | RELATIONAL DATA MODEL |
|---|---|---|
| Data is organized into a tree-like structure. | Data is represented in the form of linked lists, that is, it is viewed as a graph in which object types are nodes and relationship types are arcs. | It makes the use of relations (tables) to represent the data. |
| It stores data using parent-child relationships. Each parent may have many children but each child has one parent. | Network data models allow each record to have multiple parent and child records. | Many relations (tables) can be related to each other with the help of mapping cardinalities, key constraints and participation constraints. |
| The entity types are related to each other using 1:N mapping (one to many) | Supports all types of mapping cardinalities. (one to one, one to many, many to one, many to many) | Supports all types of mapping cardinalities. (one to one, one to many, many to one, many to many) |
| It may contain repeated entries and hence does not ensure removal of data redundancy. | Data redundancy is checked to a certain extent | Unnecessary duplication of data is reduced by various means, thus ensuring removal of data redundancy. |
| No predicate logic. | No predicate logic. | The relational data model is based on predicate logic. |
| The model is described in graphical terms. | This model, again, is described in graphical terms. | The relational data model is the first to be described in formal mathematical terms. |
| Procedural nature of data manipulation. | Procedural nature of data manipulation. | It uses the object oriented concepts for data manipulation |
| It provides a low level interface. | It again provides a low level interface which is not much declarative. | It offers a higher level, more declarative interface. |
| The most recognized and used hierarchical data models are IMS developed by IBM and windows registry developed by Microsoft. | IDMS, Univac DMS, RDM server are some of the network databases. | Microsoft’s SQL server, Oracle database, IBM’s DB2 etc, are some of the widely used relational databases. |
Until the early 1980’s, the hierarchical and network models were used extensively, but as the hardware became faster, the extra productivity and flexibility of the relational model led to the gradual obsolescence of the network and hierarchical models in corporate enterprise usage.
Further reading :
p105-Silberschatz-Data-Models-1996.pdf [1]
p112-Navathe-evolution of data modeling for databases. [2]
p18-Date-A formal definition of the relational model. [3]
Related topics :