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This post contains RDBMS introduction, EF Codd rules for RDBMS, Disadvantages of RDBMS and Advantages of RDBMS.
Let’s start the post now.
Flat database and a Relational database are two types of database.
A RDBMS is a DBMS that is based on the relational model introduced by Dr. Edgar F. Codd and it should satisfy the 12 Codd’s rule but in practice there is no DBMS that satisfies all these rules. In relational database, there are tables to store data.
The columns define which kind of information to be stored in the table. An individual column is created for each type of data you wish to store (i.e. Name, Age, City and so on). The row contains the actual values for these specified columns. So for every row, one value will be there for each and every column. For example a table with columns (Name, Age and City) could have a row with the values (Shravani, 55, Chennai)
The most important feature of relational database is that a single database is spread across several tables and all these tables are related to each other. For example, assume the company database. You can group different parts of your company into separate tables to store information logically. For example – tables might be: Employees, Department and Customers.
Each table would then contain columns specific to these three areas. To store information related to each employee, the Employees table might have the columns: EmpName, JoiningDate, Post, Age, ContactNo, and Salary. To store information related to each department, the Departments table might have the columns: DepartmentNo, DepartmentName, DepartmentLocation and DepartmentMgr.
Few examples of RDBMS are PostgresSQL, Oracle, Microsoft SQL Server, Sybase etc.
Now, we will learn about EF Codd rules for rdbms that states what should be quality for rdbms.
Let’s move to next section on rdbms introduction i.e. EF Codd rules.
E.F. Codd Rules For RDBMS
Note that based on these rules there is no fully relational database management system available today.
Rules 6, 9, 10, 11, 12 are a bit difficult to satisfy.
- Foundation Rule: A RDBMS must manage its stored data using only its relational capabilities.
- 1. Information Rule: Information stored in the database should be represented on 1 and only 1 way – as values in the table.
- 2. Guaranteed Access Rule: Each and every datum (atomic value) which is atomic in nature is guaranteed to be accessible by a
combination of table name, primary key value and column name.
- 3. Systematic Treatment of Null Values: Null values (which are distinct from empty character string or a string of blank characters and distinct from zero or any other number) are supported in the fully relational DBMS for representing missing information in a systematic way, independent of data type.
- 4. Dynamic On-line Catalog Based on the Relational Model: Data Dictionary of the database is the collection of information related to database i.e. table names, column names etc. All this metadata is called as Data Dictionary; only authorized users can apply the same relational language to its interrogation as they apply to regular data.
- 5. Comprehensive Data Sublanguage Rule: A relational system supports various languages and various modes of terminal use. But, there should be at least one language whose statements have ability to support data definition, view definition, data manipulation (interactive and by program), integrity constraints, authorization, transaction boundaries (begin, commit and rollback).
- 6. View Updating Rule: Views are said to be virtual tables in database. Views can consist of data from two or more tables. Views help in abstraction of data. Whatever updates are done in the base tables should be updated in the views.
- 7. High-level Insert, Update and Delete: The capability of handling a base relation or a derived relation as a single operand applies not only to the retrieval of data but also to the insertion, update and deletion of data.
- 8. Physical Data Independence: Application programs and terminal activities remain logically unimpaired whenever any changes are made in either storage representation or access methods.
- 9. Logical Data Independence: Application programs and terminal activities remain logically unimpaired when information preserving changes of any kind that theoretically permit unimpairment are made to the base tables.
- 10. Integrity Independence: Integrity constraints specific to a particular relational database must be definable in the relational data
sublanguage and storable in the catalog, not in the application programs.
- 11. Distribution Independence: The data manipulation sublanguage of a relational DBMS must enable application programs and terminal activities to remain logically unimpaired whether and whenever data are physically centralized or distributed.
- 12. No subversion Rule: If a relational system supports a low-level (single-record-at-a-time) language, that low-level language cannot be used to subvert or bypass the integrity rules or constraints expressed in the higher-level (multiple-records-at-a-time) relational language.
These were EF Codd rules for rdbms.
Now, we will see next topic on rdbms introduction i.e. Advantages/Disadvantages of RDBMS
Advantages of RDBMS
- In RDBMS, relationship between two tables is specified at the time of table creation using foreign keys.
- Most of the RDBMS supports client/server architecture.
- Several tables can be grouped in one database.
- Maintains multiple levels of security- at logging in at OS level, Command prompt level, Object level.
Disadvantages of RDBMS
- Increased costs: RDBMS requires sophisticated hardware and software and highly skilled personnel. Also, cost of maintaining rdbms is high.
- Frequent upgrade/replacement cycles: DBMS vendors frequently updates their product. So, user too need to update their product which require time, cost and other thing
That’s end of tutorial on rdbms introduction.