Database: database can be defined as a collection of information stored at a particular place written in a predetermined manner, belongs to a particular topic.
DBMS: (DATA BASE MANAGEMENT SYSTEM): it is defined as software which is present inside the database which is used o maintain or manage the data within the database
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In the above diagram, if the user needs any info from the database. He has to contact with dbms, then the dbms goes to the database, takes the information from the database and gives it back to the user.
Database models: these models are broadly divided into the following types:
1. FMS/FDMS
2. HMS/HDMS
3. NDBMS
4. RDBMS
5. ORDBMS
6. OODBMS
v FMS(file management system):this was the first model released in the late 1950’s
In this model the data is stored in the form of sequential manner or continuous stream of characters.
· The best example for this is radio cassette.
· The main disadvantage of this model is, if the user wants to find out any value, then he needs to start searching for the file from the beginning of the file.
· The programming language C,COBAL supports this model.
· This model is also called as flat file system.
v HMS(hierarchy model system): This model was developed by IBM at 1968 while developing a project called IMS” information management system”.
· This model was developed on the basis of an operating system called “MS-DOS”.
· In this model data is always stored in the form of tree structure or indefinite levels .
· The top level can be called as root. The 2nd,3rd and 4th levels can be called as parent, child, and sibling level respectively.
· The advantage of this model is user can easily identify the value without wasting much time.
· The drawbacks include:
1. In this model only one user can share the database at a time.
2. If you want to add one more level to the existing level. Then the user has to reconstruct the entire tree structure.
v NDBMS(network database management system): ): This model was developed by IBM at 1969(IMS project).
¨ This model was developed on the basis of an operating system called “MULTICS”.
¨ Network: connecting two or more computer system using cable.
¨ Advantages of NDBMS: main advantage is that, more than one user can share the database at a time.
¨ Disadvantage: lack of security of centralized database.
¨ As more than one user can share the database, so the two inputs may be redundant.
¨ It occupies a lot of memory so it leads to decrement in the system performance and increase in inconsistency.
v RDBMS(relational database management system): this database management system was developed by a German scientist called “EF CODD” in the year 1970.
Ø The reason it is called RDBMS instead of codd theory or anything else is because of the fact that this was developed on the basis of mathematical relation(i.e union and intersection)
Ø Here the relation can be defined as the commonness between any objects.
Ø Properties of RDBMS:
§ Data should be stored in the form of table .
A table can be defined as the collection of rows and columns.
The horizontal lines are called as rows and the vertical lines can be called as columns.
The intersection of row and column is called as cell.
A cell is a place where we can store data.
§ Table should not contain duplicate columns.
§ While inserting the records into the table, user need not follow any order.
§ Database should not contain duplicate objects.
§ While we define the columns into the table user need not follow any order.
Oracle is based on this RDBMS model so lets stop at this point.