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What Is Data Integrity?
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Posted Date :
December 21, 2010
Data integrity is an important feature in SQL Server. When used properly, it ensures that data is accurate, correct, and valid. It also acts as a trap for otherwise undetectable bugs within applications.
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What Is Data Integrity?
What is Data Integrity and it's categories ?
Enforcing data integrity ensures the quality of the data in the database. For example, if an employee is entered with an employee_id value of 123, the database should not allow another employee to have an ID with the same value. If you have an employee_rating column intended to have values ranging from 1 to 5, the database should not accept a value of 6. If the table has a dept_id column that stores the department number for the employee, the database should allow only values that are valid for the department numbers in the company. Two important steps in planning tables are to identify valid values for a column and to decide how to enforce the integrity of the data in the column. Data integrity falls into these categories:
1) Entity integrity
2) Domain integrity
3) Referential integrity
4) User-defined integrity
Entity Integrity: Entity integrity defines a row as a unique entity for a particular table. Entity integrity enforces the integrity of the identifier column(s) or the primary key of a table (through indexes, UNIQUE constraints, PRIMARY KEY constraints, or IDENTITY properties).
Domain Integrity: Domain integrity is the validity of entries for a given column. You can enforce domain integrity by restricting the type (through data types), the format (through CHECK constraints and rules), or the range of possible values (through FOREIGN KEY constraints, CHECK constraints, DEFAULT efinitions, NOT NULL definitions, and rules).
Referential Integrity: Referential integrity preserves the defined relationships between tables when records are entered or deleted. In MicrosoftÃâÃÂ® SQL ServerT 2000, referential integrity is based on relationships between foreign keys and primary keys or between foreign keys and unique keys (through FOREIGN KEY and CHECK constraints). Referential integrity ensures that key values are consistent across tables. Such consistency requires that there be no references to nonexistent values and that if a key value changes, all references to it change consistently throughout the database. When you enforce referential integrity, SQL Server prevents users from:
ÃâÃÂ· Adding records to a related table if there is no associated record in the primary table.
ÃâÃÂ· Changing values in a primary table that result in orphaned records in a related table.
ÃâÃÂ· Deleting records from a primary table if there are matching related records.
For example, with the sales and titles tables in the pubs database, referential integrity is based on the relationship between the foreign key (title_id) in the sales table and the primary key (title_id) in the titles table.
User-Defined: Integrity User-defined integrity allows you to define specific business rules that do not fall into one of the other integrity categories. All of the integrity categories support user-defined integrity (all column- and table-level constraints in CREATE TABLE, stored procedures, and triggers).
Explain Constraints Of Data Integrity?
i) A PRIMARY KEY constraint is a unique identifier for a row within a database table. Every table should have a primary key constraint to uniquely identify each row and only one primary key constraint can be created for each table. The primary key constraints are used to enforce entity integrity.
ii) A UNIQUE constraint enforces the uniqueness of the values in a set of columns, so no duplicate values are entered. The unique key constraints are used to enforce entity integrity as the primary key constraints.
iii) A FOREIGN KEY constraint prevents any actions that would destroy links between tables with the corresponding data values. A foreign key in one table points to a primary key in another table. Foreign keys prevent actions that would leave rows with foreign key values when there are no primary keys with that value. The foreign key constraints are used to enforce referential integrity.
iv) A CHECK constraint is used to limit the values that can be placed in a column. The check constraints are used to enforce domain integrity.
v) A NOT NULL constraint enforces that the column will not accept null values. The not null constraints are used to enforce domain integrity, as the check constraints.
What are the different levels of data integrity in SQL Server?
When do you need to specify an external data source by using a linked server?
When you need to access a different instance.
What is Method used to bind the data into gridview ?
DataBind() Method used to bind the data into gridview
What is the .NET that allows the retrieval of data by a unique key?
HashTable is the .NET collection class that allows the retrieval of data by a unique key
What is managed code and managed data?
Managed code is code that is written to target the services of the Common Language Runtime (see What is the Common Language Runtime?). In order to target these services, the code must provide a minimum level of information (metadata) to the runtime. All C#, Visual Basic.NET, and _JScript.NET code is managed by default. Visual Studio.NET C++ code is not managed by default, but the compiler can produce managed code by specifying a command-line switch (/CLR).
Closely related to managed code is managed data-data that is allocated and de-allocated by the Common Language Runtime's garbage collector. C#, Visual Basic, and _JScript.NET data is managed by default. C# data can, however, be marked as unmanaged through the use of special keywords. Visual Studio.NET C++ data is unmanaged by default (even when using the /CLR switch), but when using Managed Extensions for C++, a class can be marked as managed by using the __gc keyword. As the name suggests, this means that the memory for instances of the class is managed by the garbage collector. In addition, the class becomes a full participating member of the .NET Framework community, with the benefits and restrictions that brings. An example of a benefit is proper interoperability with classes written in other languages (for example, a managed C++ class can inherit from a Visual Basic class). An example of a restriction is that a managed class can only inherit from one base class.
What is data structure?
A data structure is a way of organizing data that considers not only the items stored, but also their relationship to each other. Advance knowledge about the relationship between data items allows designing of efficient algorithms for the manipulation of data.
List out the areas in which data structures are applied extensively?
3.Database Management System,
4.Statistical analysis package,
What are the major data structures used in RDBMS, Network data model & Hierarchical data model.
RDBMS - Array (i.e. Array of structures)
Network data model - Graph
Hierarchical data model - Trees
What is the data structures used to perform recursion?
Stack. Because of its LIFO (Last In First Out) property it remembers its 'caller' so knows whom to return when the function has to return. Recursion makes use of system stack for storing the return addresses of the function calls.
Every recursive function has its equivalent iterative (non-recursive) function. Even when such equivalent iterative procedures are written, explicit stack is to be used.
What operator tests column for the absence of data?
IS NULL operator
Describe the three levels of data abstraction?
The are three levels of abstraction:
1.Physical level: The lowest level of abstraction describes how data are stored.
2.Logical level: The next higher level of abstraction, describes what data are stored in database and what relationship among those data.
3.View level: The highest level of abstraction describes only part of entire database.
Define the "integrity rules"
There are two Integrity rules.
1.Entity Integrity: States that "Primary key cannot have NULL value"
2.Referential Integrity: States that "Foreign Key can be either a NULL value or should be Primary Key value of other relation.
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