Procedures

Declaration Statements in VB.NET

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Declaration Statements

The declaration statements are used to name and define procedures, variables, properties, arrays, and constants. When you declare a programming element, you can also define its data type, access level, and scope.

The programming elements you may declare include variables, constants, enumerations, classes, structures, modules, interfaces, procedures, procedure parameters, function returns, external procedure references, operators, properties, events, and delegates.

Following are the declaration statements in VB.Net:

S.N Statements and Description Example
1 Dim Statement
Declares and allocates storage space for one or more variables.
Dim number As IntegerDim quantity As Integer = 100Dim message As String = “Hello!”
2 Const Statement
Declares and defines one or more constants.
Const maximum As Long = 1000Const naturalLogBase As Object = CDec(2.7182818284)
3 Enum Statement
Declares an enumeration and defines the values of its members.
Enum CoffeeMugSize    Jumbo    ExtraLarge    Large    Medium    SmallEnd Enum
4 Class Statement
Declares the name of a class and introduces the definition of the variables, properties, events, and procedures that the class comprises.
Class BoxPublic length As DoublePublic breadth As Double   Public height As DoubleEnd Class
5 Structure Statement
Declares the name of a structure and introduces the definition of the variables, properties, events, and procedures that the structure comprises.
Structure BoxPublic length As Double           Public breadth As Double   Public height As DoubleEnd Structure
6 Module Statement
Declares the name of a module and introduces the definition of the variables, properties, events, and procedures that the module comprises.
Public Module myModuleSub Main()Dim user As String = InputBox(“What is your name?”) MsgBox(“User name is” & user)End Sub End Module
7 Interface Statement
Declares the name of an interface and introduces the definitions of the members that the interface comprises.
Public Interface MyInterface    Sub doSomething()End Interface
8 Function Statement
Declares the name, parameters, and code that define a Function procedure.
Function myFunction(ByVal n As Integer) As Double     Return 5.87 * nEnd Function
9 Sub Statement
Declares the name, parameters, and code that define a Sub procedure.
Sub mySub(ByVal s As String)    ReturnEnd Sub
10 Declare Statement
Declares a reference to a procedure implemented in an external file.
Declare Function getUserNameLib “advapi32.dll” Alias “GetUserNameA” (  ByVal lpBuffer As String,   ByRef nSize As Integer) As Integer
11 Operator Statement
Declares the operator symbol, operands, and code that define an operator procedure on a class or structure.
Public Shared Operator +(ByVal x As obj, ByVal y As obj) As obj        Dim r As New obj’ implemention code for r = x + y        Return r    End Operator
12 Property Statement
Declares the name of a property, and the property procedures used to store and retrieve the value of the property.
ReadOnly Property quote() As String     Get         Return quoteString    End Get End Property
13 Event Statement
Declares a user-defined event.
Public Event Finished()
14 Delegate Statement
Used to declare a delegate.
Delegate Function MathOperator(     ByVal x As Double,     ByVal y As Double ) As Double

 

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Components of the Database System Environment

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Components of the Database System Environment

There are five major components in the database system environment and their interrelationship  are –

  • Hardware
  • Software

    DBMS Application Users
    DBMS Application Users
  • Data
  • Users
  • Procedures

1. Hardware: The hardware is the actual computer system used for keeping and accessing the database.

2. Software: The software is the actual DBMS. Between the physical databases itself (i.e. the data as actually stored) and the users of the system is a layer of software, usually called the Database Management System or DBMS. All requests from users for access to the database are handled by the DBMS. One general function provided by the DBMS is thus the shielding of database users from complex hardware-level detail.

omponents of the Database System
omponents of the Database System

3. Data: It is the most important component of DBMS environment from the end users point of view. As shown in figure that data acts as a bridge between the machine components and the user components. The database contains the operational data and the meta-data, the ‘data about data’.

4. Users: There are a number of users who can access or retrieve data on demand using the applications and interfaces provided by the DBMS. Each type of user needs different software capabilities. The users of a database system can be classified in the following groups, depending on their degrees of expertise or the mode of their interactions with the DBMS. The users can be:

• Naive Users

• Online Users

• Application Programmers

• Sophisticated Users

• Data Base Administrator (DBA)

5. Procedures: Procedures refer to the instructions and rules that govern the design and use of the database. The users of the system and the staff that manage the database require documented procedures on how to use or run the system.

These may consist of instructions on how to:

• Log on to the DBMS.

• Use a particular DBMS facility or application program.

• Start and stop the DBMS.

• Make backup copies of the database.

• Handle hardware or software failures.

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