RDBMS refers to Relational Database Management System. It is a database management system based on the relational model introduced by Dr. E. Codd in 1970 in his paper titled “A Relational Model of Data for Large Shared
Data Banks”. The relational model identifies the database as a collection of objects or relations, and the relationships between them. Some popular RDBMS software include Microsoft SQL server. SQL is a Structured Query Language, used by developers to query the relational database for data retrieval, modification, insertion and deletion.
A relation is structured in the form of a two dimensional table. The rows of the table are called as the tuples and the columns of the table are known as fields or attributes. Tuples give information about records of the database, while attributes give information about the type of records being saved. For example, given below is a table with tuples and attributes:
Founder
ID
|
Name
|
Age
|
Company
|
1
|
Mark
|
34
|
Facebook
|
2
|
Bill
|
56
|
Microsoft
|
3
|
Steve
|
54
|
Apple
|
Here, the attributes or fields are ID, Name, Age and Company. The tuples are all three rows or records. Notice the first column ID. This column can be used to identify each record distinctly. Such an attribute can be labelled as a primary key. The benefit of a primary key is that it can enforce the uniqueness in all records, i.e, if ID is labelled as a primary key, then no two records can have the same ID. A primary key of one table becomes a foreign key in another table. Suppose we have another table as follows:
Person
ID
|
Name
|
Founder_ID
|
Works At
|
1
|
Mark
|
1
|
Facebook
|
2
|
Mark
|
3
|
Apple
|
3
|
Steve
|
3
|
Apple
|
In this table, the Founder_ID refers to the ID attribute from the first table.
Operations on a Relational Database
There are three basic operations carried out on a relational database. These are:
- Select: Select is used to derive a subset of the tuples of a relation that satisfies a certain condition. Eg: SELECT age '34'(Founder) will produce a set of records where the age of founder is 34.
- Join: Join is used to join two relational tables. It is usually the cross product of the two tables. Eg: Founder JOIN Person will join the above two tables.
- Project: Project is used to derive a subset of the attributes of a relation, by giving the names of the attributes we want to return. Eg: PROJECTID, Name(Founder) will produce the founder table with only two columns - ID and Name.
There are two approaches to database design, both of which must be equally considered. One is logical design, which refers to the way the database administrator organises data in the form of tables, and the other is physical design, which refers to the way data is stored on disks.
Tuesday, 13 September 2016
