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Consistency constraints in dbms?
it describes the instance of one entity is associated with each instances of an entity
depending upon the range of cardinality constraints are two types
depending upon the range of cardinality constraints are two types
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Constraint, in Project Management terms, means a factor that affects when an activity can be scheduled. ---------------------------------------------------------------------…--------------------- It can be some kind of a limitation or restriction. webmaster at service.ztronics.com ------------------------------------------------------------------------------------------ Since this question has been categorised in Database Design, I will assume you mean what is a a constraint within a database... You can have primary key, foreign key, alternate key and domain (aka check) constraints. Domain contraints apply to a single field in a single row - e.g. whether or not nulls are allowed, or an enumerated list of allowed values. Primary keys and alternate keys ensure that a for the column(s) in the key each row in the table has a unique value (or set of values if the key is composite). Foreign keys ensure that if one table references another, that the reference exists in the parent table. This is normally linked to the primary key e.g. this example (Oracle syntax) demonstrates these create table employee ( employee_id number not null, first_name varchar2(100) not null, middle_names varchar2(100) null, last_name varchar2(100) not null, sex char(1), ni_number varchar2(10) not null, CONSTRAINT pk_employee PRIMARY KEY (employee_id), CONSTRAINT ak_national_insurance UNIQUE (ni_number), CONSTRAINT cc_sex CHECK sex in ('M', 'F') ); create table emp_salary_hist ( employee_id number not nul,l pay_review date not null, pay_grade number not null, salary number not null, CONSTRAINT pk_emp_sal_hist PRIMARY KEY (employee_id, pay_review), CONSTRAINT fk_employee FOREIGN KEY (employee_id) REFERENCES employee(employee_id) );
dBm is decibel power unit referenced to 1 milliwatt. Look at the related links for conversion: voltage to dBm, dBu, and dBV.
DataBase Management System (DBMS) is a software package that allows data to be effectively stored, retrieved and manipulated and the data stored in a DBMS packege can be ac…cessed by multiple users and by multiple application programs like (SQL Server, Oracle, Ms-Access) ..
it is the power ratio in decibels No, it isn't. dB on its own is a ratio. But when dB has a suffix, the figure is an absolute measurement, not a ratio. For instance, d…Bm is a measurement of power compared to 1mW. 0dBm means zero difference between 1mW and the measured figure. In other words the measured figure is also 1mW. 3dBm is 3dB greater than 1mW. -3dB is 3dB less than 1mW. etc. Another suffix is W. 0dBW being 1 watt. There are many more suffixes, some of which are used in only a few specialised cases.
Data Base Management System
each column contains same type of data thus when you select a data type for a particular domain then DBMS will not accept any value of other data type. Further information …contributed by Ramona Maxwell. Please visit www.sqlsolver.com: Domain constraints are a user-defined data type which enforces the integrity of the standard data types. A domain consists of all values permitted in a column. In constructing your database you would first select a standard data type such as VARCHAR or INT. You could then constrain or limit the data using NOT NULL, UNIQUE, CHECK, PRIMARY KEY or FOREIGN KEY. For example the CHECK constraint could limit INT data within your domain [column] to numbers less than 5000. You would thus define a custom data type using domain constraints.
The term integrity means to correctness and completeness of the data in data base. A relational data base is collection of related table. Table contains various information. T…ables are connected by the foreign key relationship. When the contains with the certain command, insert, delete, update.The integrity of the data can be loss in many different waves. .
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In SQL data consistency is that whenever a transaction is performed, it sees a consistent database. During the transaction, if the database is not consistent, then there are t…wo reasons for it, which are as follows: 1-database failure (software or hardware failure) 2-multiple accesses data consistency makes sure data integrity and vice versa. :)
Constraints within a database are rules which control values allowed in columns and also enforce the integrity between columns and tables. An example of a column constraint… would be a 'CHECK' constraint on a column to limit the values allowed. For example, you could specify the datatype of a column to be tinyint, which can store values from 0-255, but then specify a CHECK constraint that limits values of 1-99, like this; CREATE TABLE my_example (SomeColumn tinyint, CONSTRAINT ChkValue CHECK (SomeColumn BETWEEN 1 and 99 )) Another common constraint is UNIQUE, which ensures that the value in a column is unique within the table. This would be used on something like a customer code in a customer table, where you need to ensure that no two customers have the same code. This can also be done with a PRIMARY KEY constraint. To enforce integrity, you can specify that a column has a FOREIGN KEY relationship with the values in another table, a concept at the heart of a relational database. An example of this would be a FK constraint on a 'sales order' table linking the order customer code back to the customer table. The FK serves two functions; (1) The code entered on the order must be valid and (2) the customer can't be deleted if there are any orders. The simplest and most common constraint is the nullability of a column, specified with the NULL and NOT NULL operators when creating columns; CREATE TABLE MyExample (ID int NOT NULL, Description varchar(50) NULL).
A foreign key is a type of constraint. In this example the value in a field must be the same as some value in a defined field in another table. Example in a Customer Table y…ou might have a Column (field) named StatusID You would define a foreign key to the table Status, field StatusID. The value in the Customer table, StatusID column must be an entry existing in the Status Table, StatusID column. There are many constraints. The fact that a column can not be NULL (Left blank) is a constraint. Defining what KIND of data, or range of data that can be entered in a column is a constraint.
Constraints are holding back or regulation. There are constraints on the government in the Bill of Rights. A criteria is a set of standards or specifications. The criteria for… winning the game was to reach a total of ten answers.
so it role is basically to manage the database
DBMS stands for data base management system. DBMS is a collectionof programs that enables users to create and maintain a database.The DBMS is a general purpose software system… used to facilitatethe process of defining, constructing and manipulating data basesfor various applications. features of DBMS: 1.Data independence 2.Efficient data access 3.Data integrity & security 4.Data administration 5.Reduced application development time
DBMS is database management system and it stores data that are related. DBMS maintains data security and integrity as well.