What is RDBMS?
RDBMS stands for Relational Database Management System.
R-DBMS is model of DBMS (Database Management System) and its relational is extra feature to normal DBMS and Relational feature maintaining the relation of database objects.
RDBMS introduced by E. F. Codd early 1980s.
E.F Codd was a Computer Scientist and they have proposed 12 rules(0 to 12 total 13 rules) for RDBMS’s concept against DBMS.
MS SQL Server, IBM DB2, Oracle, MySQL, MariaDB, Postgres and Microsoft Access is popular relational databases and All Relational database support to SQL Language
What Is SQL:
SQL Stands for Structured Query Language which is specially designed to communicate with databases so its can be perform database activity like writing statement like insert, update, delete, create, alter and drop database objects,etc.
RDBMS manage and maintain entity relationship(ER) so its have major components are Table,Column(Attribute) and row(Record).
What is ER /ER Diagram:
ER Diagram is a way or system for represent Entity Relationship via model / diagram, its have 4 types of attributes
1) Composite attribute
2) Single valuable attribute
3) Stored vs derived attribute
4) Complex attribute
Composite attribute: Single attribute can be divides into multiple smaller subpart and each subpart represent individual information or meaning like Address attribute is composite attribute and it can be divided into multiple subpart like Street Address, City Name, State name, country name, Pin Code, etc.
Single valuable attribute: its always represent single values with unique meaning so it is a unique values like Student Roll number, Registration number, OPD number etc.
Stored vs derived attribute: store information which are derived means get other information from stored information like age attribute stored but birth year derived.
Complex attribute: when any attribute represents group of information and its can be separate by () and multiple value represent by square bracket []. Like add_phone (address and phone) attribute store date like
([Phone(Code, phone_number),
address(street, plot number, city, state )])
What is Entity :
Entity is a object(like table) and its always uniquely identify in a module/diagram like department, employee etc.
What is Relationships:
Relationship is a situation or link that exists between two object (relational model) like one table has a foreign key that references the primary key of the other table. Like County table have primary key and foreign key in a Province table so both table’s linking object called Relation other way Country and Province both called entity and both object internally lined so we can say entity relationship.
RDBMS Codd’s Rule for Relational DBMS:
Rule 0: The foundation rule:
system to qualify as an RDBMS that system must be able to manage data bases entirely through its relational capabilities.
Rule 1: The information rule:
All data and metadata to be stored and data represent in cells of tables.
Rule 2: The guaranteed access rule:
Each and every data in a relational base is guaranteed to be logically accessible by resorting to a combination of table name,primary key represented by a specific row value and column represented by attribute value.
Rule 3: Systematic treatment of null values:
Null values are must be support to databases. They should be uniformly considered as ‘missing information’. Null values are independent of any data type. They should not be mistaken for blanks or zeroes or empty strings.
Rule 4: Active Online Catalog :
The data’s metada is represented as same way as ordinary data, so authorized users can apply the same relational language to its interrogation as they apply to the regular data.
Rule 5: Comprehensive Data Sub-language Rule:
A database should be accessible by a language supported for definition, manipulation and transaction management operation.
Rule 6: The view updating rule:
All views that are theoretically updatable are also updatable by the system.
Rule 7: Relational Level Operation:
Must be capability for Insert, Update, Delete operations at each level of relations.
Rule 8: Physical data independence:
When change physical location of a table should not enforce modification at application level.
Rule 9: Logical data independence:
If there is change in the logical structure of the database the user view of data should not change.
Rule 10: Integrity independence:
Integrity constraints modified at database level should not enforce modification at application level.
Rule 11: Distribution independence:
Distribution of data over various locations should not be visible to end-users.
Rule 12: The nonsubversion rule:
Low level access to data should not be able to bypass integrity rule to change data.
source: wikipedia.org
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