Relational Model Introduction | Database Management System

Relational Model Introduction | Database Management System

Relational Model Introduction : We have discussed the E-R Model, a technique for building a logical model of an enterprise. Logical models are high level abstract views of an enterprise data. In building these models little thought is given to representing or retrieving data in the computer. At the next lower level, a number of data models are available that provide a mapping for a logical data model like the E-R model. These models specify a Conceptual view of the data as well as a high level view of the implementation of the database on the computer. They do not concern themselves with the detailed bits and bytes view of the data. There are three widely used data models at this intermediate level. These are relational, hierarchical and network models, All the three data models provide facilities for representing entities and their attributes as well as relationships. The data about entities and their attributes is handled in a similar way in all the three models. The representation is a record which is a collection of attribute values (including an identifier of the entity) although the structure of the record may be somewhat different. The relationships are however represented very differently in the three models and we will discuss these differences in detail. We start by looking at the simplest model; the relational model.

A Relational database management system (RDBMS) is a database management System (DBMS) that is based on the relational model as introduced by E.F. Codd. Relational databases are the most common kind of database in use today.

The Relational model uses relation (table) to represent both entities and relationships among entities. A relation may be Visualized as a table. However table is just one of the way, among many, to represent a relation.

The relational model was proposed by E. F. Codd in 1970. A relational database is a database that conforms to the relational model, and refers to a database’s data and Schema (the database’s Structure of how those data are arranged). The term “relational database” is sometimes informally used to refer to a relational database management System, which is the Software that is used to Create a relational database.

A relation is defined as a set of tuples that have the same attributes. A tuple usually represents an object and information about that object. Objects are typically physical objects or Concepts. A relation is usually described as a table, which is organized into rows and Columns. All the data referenced by an attribute are in the same domain and conform to the same Constraints. The following figure explains main RDBMS terms:

The relational model specifies that the tuples of a relation have no specific Order and that the tuples, in turn, impose no order on the attributes. Applications access data by Specifying queries, which use operations such as select to identify tuples, project to identify attributes, and join to Combine relations. Relations can be modified using the insert, delete, and update operators. New tuples can supply explicit values or be derived from a query. Similarly, queries identify tuples for updating or deleting.

 

Now look at the list/table given below which list explain main RDBMS terms and examples based on above relations:

Relational databases Store data in tables (relations) that are two dimensional. The tables have rows (records or objects) and columns (fields or attributes). Data items at an intersection of a row and a column are called a cell and consist of attribute values. Data stored is simple data such as integers, real numbers or string values. Multiple values may not be stored in one cell. Relational database tables are “normalized” so data is not repeated more often than necessary. All table columns depend on a primary key (a unique value in the column) to identify the column. Once the specific column is identified, data from one or more rows associated with that Column may be obtained or changed. Relational databases are sets of tables. One table file is not a relational database. A relational database server is not the same as a relational database. A relational database can be a file with sets of tables. The relational database server includes the ability to Service requests to get or change data from remote clients. Relational database servers use Structured Query Language (SOL), as a data manipulation language to interface between itself and the clients. SQL is the standard for getting and storing data in an RDBMS. Relational database servers provide:

  • Data Management
  • Transaction processing
  • Data integrity: Provides for multiple access at the same time (concurrency) between multiple processes/users. This is done so data is not displayed nor saved in a fashion where one change is lost. Various locking mechanisms are used to support this.
  • Data backup and recovery.
  • Data security: Provides for user authentication, and levels of data access privileges.