Database SecurityDatabase security has many different layers, but the key aspects are:AuthenticationUser authentication is to make sure that the person accessing the database is who he claims to be. Authentication can be done at the operating system level or even the database level itself. Many authentication systems such as retina scanners or bio-metrics are used to make sure unauthorized people cannot access the database.AuthorizationAuthorization is a privilege provided by the Database Administer. Users of the database can only view the contents they are authorized to view. The rest of the database is out of bounds to them.The different permissions for ... Read More

Locks are an integral part to maintain concurrency control in DBMS. A transaction in any system implementing lock based concurrency control cannot read or write a statement until it has obtained the required locks.There are two types of locks in Lock based protocols. These are:Binary Locks - These can only be in one of two states, locked or unlocked.Shared/Exclusive Locks - Shared locks are acquired when only read operation is to be performed. Shared locks can be shared between multiple transactions as there is no data being altered. Exclusive locks are used when write operation is performed. Only the transaction holding the ... Read More

In a distributed database management system, the database is not stored at a single location. Rather, it may be stored in multiple computers at the same place or geographically spread far away. Despite all this, the distributed database appears as a single database to the user. A diagram to better explain this is as follows:As seen in the figure, the components of the distributed database can be in multiple locations such as India, Canada, Australia, etc. However, this is transparent to the user i.e the database appears as a single entity.Types of Distributed Database Management SystemThe following are the types ... Read More

The different types of functions in Oracle are −Oracle String FunctionsOracle Numeric FunctionsOracle Date FunctionsMore details about these functions are given as follows −Oracle String FunctionsThe following are the Oracle String Functions −ASCII(str)This function returns the ASCII or numeric value of the first word in the string str provided. If it is an empty string, it returns 0. For example:SQL> SELECT ASCII('Apple'); +---------------------------------------------------------+ | ASCII('Apple') | +---------------------------------------------------------+ | 65 | +---------------------------------------------------------+ 1 row in set (0.00 sec)This returns the ASCII value of A i.e. 65 as it is the first character in the string.CONCAT(str1, str2…..strn)This function returns the string that ... Read More

When a SQL statement is executed in Oracle, the temporary context area is created. This area contains all the relevant information relating to the statement and its execution. The cursor is a pointer to this context area and allows the PL/SQL program to control this area.There are two types of Cursors.Implicit CursorsExplicit CursorsLet us begin with Implicit Cursors −Implicit CursorsWhenever an SQL statement is executed, the implicit cursors are automatically created. This happens if there is no explicit cursor for the particular statement. Implicit cursors cannot be controlled by the programmers.There are many different attributes for Implicit Cursors. Some of ... Read More

PL/SQL is a block structured language i.e the code of PL./SQL is written in the form of blocks. PL/SQL also contains the robustness, security and portability of the Oracle database.Each block of PL/SQL contains the following subparts −Declarations -  This section contains all the items that needs to be declared before the program such as variables, subprograms etc. This section contains the keyword DECLARE at its start. In general, Declarations is an optional subpart of the PL/SQL program.Executable Commands -  This section of the PL/SQL code contains the executable statements. It contains BEGIN and END at its starting and ending. ... Read More

Packages are SQL procedures, functions, variables, statements etc. that are grouped into a single unit. Many different applications can share the contents of a package, as it is stored in the database.Parts of a PackageThe following are the parts of a package in Oracle −Package SpecificationThe package specifications contains information about all the procedures, functions, variables, constants etc. stored inside it. It has the declaration of all the components but not the code.All the objects that are in the specification are known as public objects. If there is any object that is not available in the specification but is coded ... Read More

The contents of a distributed database are spread across multiple locations. That means the contents may be stored in different systems that are located in the same place or geographically far away. However, the database still appears uniform to the users i.e the fact that the database is stored at multiple locations is transparent to the users.The different components of a distributed database are −Let us now discuss them one by one −UsersThere are many users who use the distributed database. For them, the fact that the database is spread across multiple locations is transparent and they perceive the database ... Read More

The distributed database management system contains the data in multiple locations. That can be in different systems in the same place or across different geographical locations.As shown in the below example −The database is divided into multiple locations and stores the data in Site1, Site2, Site3 and Site4.The advantages and disadvantages of Distributed database management systems are as follows −Advantages of DDBMSThe database is easier to expand as it is already spread across multiple systems and it is not too complicated to add a system.The distributed database can have the data arranged according to different levels of transparency i.e data ... Read More

When there is a relationship between two entities of the same type, it is known as a recursive relationship. This means that the relationship is between different instances of the same entity type.Some examples of recursive relationship can be shown as follows −An employee can supervise multiple employees. Hence, this is a recursive relationship of entity employee with itself. This is a 1 to many recursive relationship as one employee supervises many employees.A person can have many children who are also persons. Hence, this is a recursive relationship of entity person with itself. This is a 1 to many recursive ... Read More