A database is a collection of information that is organized. So that it can easily be accessed, managed, and updated.
DBMS stands for Database Management System. It is a collection of programs that enables user to create and maintain a database.
The database and DBMS software together is called as Database system.
I. Redundancy is controlled.
II. Providing multiple user interfaces.
III. Providing backup and recovery
IV. Unauthorized access is restricted.
V. Enforcing integrity constraints.
It is a process of analysing the given relation schemas based on their Functional Dependencies (FDs) and primary key to achieve the properties
(2). Minimizing insertion, deletion and update anomalies.
A collection of conceptual tools for describing data, data relationships data semantics and constraints.
This data model is based on real world that consists of basic objects called entities and of relationship among these objects. Entities are described in a database by a set of attributes.
This model is based on collection of objects. An object contains values stored in instance variables with in the object. An object also contains bodies of code that operate on the object. These bodies of code are called methods. Objects that contain same types of values and the same methods are grouped together into classes.
An entity is a thing or object of importance about which data must be captured.
A data base schema is specifies by a set of definitions expressed by a special language called DDL.
This language that enable user to access or manipulate data as organised by appropriate data model. Procedural DML or Low level: DML requires a user to specify what data are needed and how to get those data. Non-Procedural DML or High level: DML requires a user to specify what data are needed without specifying how to get those data
It translates DML statements in a query language into low-level instruction that the query evaluation engine can understand.
It executes low-level instruction generated by compiler..
The first normal form or 1NF is the first and the simplest type of normalization that can be implemented in a database. The main aims of 1NF are to:
1. Eliminate duplicative columns from the same table.
2. Create separate tables for each group of related data and identify each row with a unique column (the primary key).
A functional dependency X Y is full functional dependency if removal of any attribute A from X means that the dependency does not hold any more.
A relation schema R is in 2NF if it is in 1NF and every non-prime attribute A in R is fully functionally dependent on primary key.
A relation is in third normal form if it is in Second Normal Form and there are no functional (transitive) dependencies between two (or more) non-primary key attributes.
A table is in Boyce-Codd normal form (BCNF) if and only if it is in 3NF and every determinant is a candidate key.
Fourth normal form requires that a table be BCNF and contain no multi-valued dependencies.
A query with respect to DBMS relates to user commands that are used to interact with a data base.
The phase that identifies an efficient execution plan for evaluating a query that has the least estimated cost is referred to as query optimization..
Atomicity-Atomicity states that database modifications must follow an all or nothing rule. Each transaction is said to be atomic. If one part of the transaction fails, the entire transaction fails.
Aggregation - A feature of the entity relationship model that allows a relationship set to participate in another relationship set. This is indicated on an ER diagram by drawing a dashed box around the aggregation.
Two important pieces of RDBMS architecture are the kernel, which is the software, and the data dictionary, which consists of the system- level data structures used by the kernel to manage the database..
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