What is RDBMS?

RDBMS stands for Relational Database Management System. RDBMS is the basis for SQL, and for all modern database systems like MS SQL Server, IBM DB2, Oracle, MySQL, and Microsoft Access.
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.

Codd Rules:

Rule 0 – Foundation Rule:

A relational database management system must manage its stored data using only its relational capabilities.

Rule 1 – Information Rule:

All information in the database should be represented in one and only one way – as values in a table.

Rule 2 – Guaranteed Access Rule:

Each and every datum (atomic value) is guaranteed to be logically accessible by resorting to a combination of table name, primary key value and column name.

Rule 3 – Systematic Treatment of Null Values:

Null values (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.

Rule 4 – Dynamic On-line Catalog Based on the Relational Model:

The database description is represented at the logical level in the same way as ordinary data, so authorized users can apply the same relational language to its interrogation as they apply to regular data.

Rule 5 – Comprehensive Data Sublanguage Rule:

A relational system may support several languages and various modes of terminal use. However, there must be at least one language whose statements are expressible, per some well-defined syntax, as character strings and whose ability to support all of the following is comprehensible:

  • Data definition
  • View definition
  • Data manipulation (interactive and by program)
  • Integrity constraints
  • Authorization
  • Transaction boundaries (begin, commit, and rollback)

Rule 6 – View Updating Rule:

All views that are theoretically updateable are also updateable by the system.

Rule 7 – High-level Insert, Update, and Delete:

The capability of handling a base relation or a derived relation as a single operand applies nor only to the retrieval of data but also to the insertion, update, and deletion of data.

Rule 8 – Physical Data Independence:

Application programs and terminal activities remain logically unimpaired whenever any changes are made in either storage representation or access methods.

Rule 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.

Rule 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.

Rule 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.

Rule 12 – Nonsubversion Rule:

If a relational system has or 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.

What is table?


The data in RDBMS is stored in database objects called tables. The table is a collection of related data entries and it consists of columns and rows.
Remember, a table is the most common and simplest form of data storage in a relational database.

What is field, or column?

Every table is broken up into smaller entities called fields. The fields in the CUSTOMERS table consist of ID, NAME, AGE, ADDRESS and SALARY.
A field is a column in a table that is designed to maintain specific information about every record in the table.

What is record, or row?

A record, also called a row of data, is each individual entry that exists in a table. For example there are 7 records in the above CUSTOMERS table.
A record is a horizontal entity in a table.

What is NULL value?


A NULL value in a table is a value in a field that appears to be blank which means A field with a NULL value is a field with no value.
It is very important to understand that a NULL value is different than a zero value or a field that contains spaces. A field with a NULL value is one that has been left blank during record creation.

Pictorial representation of a Table?


studenttable

Terminologies & Integrity types associated with RDBMS

PRIMARY KEYColumn used to uniquely identify a Tuple.
FOREIGN KEYColumn of a table used to establish relationship with other tables and present itself in all the relation tables.
ALTERNATE KEYColumn or combination of columns which has unique values but not selected as primary key and is not part of the primary
COMPOSITE KEYA combination of columns used to identify a unique row. Combination of customer name and address can consider to be the
Domain IntegrityIntegrity of information allowed in column.
Referential IntegrityRule states that every foreign key in the first table must either match a primary key value in the second table or must
Entity IntegrityRule states that no column that is part of a primary key can have a null value

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