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Database Programming
Databases are collections of tables that maintain and display information, often collaboratively; this information can be used for interaction with an application or gaining general knowledge. Questions about database engines and modifying or using them belong in this category.
8,803 Questions
Advantages of dbms with example?
There are several advantages of DBMS:
1. Redundancy problem can be solve
2. Security level is high
3. Referential Integrity
4. Multi user Access
5. Data Independence
By Sushil Kumar Sinha
What is complexity of binary search tree?
The complexity of binary search tree :
Search , Insertion and Deletion is O(h) . and the Height can be of O(n) ( if the tree is a skew tree).
For Balanced Binary Trees , the Order is O(log n).
What is 75 dBm converted into dBW?
dBw=dBm-30 then 75-30=45 dBw dBw=dBm-30 then 75-30=45 dBw dBw=dBm-30 then 75-30=45 dBw
Traditional file processing system lacks from DBMS in many ways . Major Disadvantage of FPS are it do not maintains data security and integrity efficiently.
* In NOT NULL constraint the particular data cannot be NULL,
* In UNIQUE constraint the same thing cannot be repeated, it must be unique,
* The primary key is simply the combination of both these constraints.
An entity is something that exists by itself, although it need not be of material existence.
Defference between direct sequential and index sequential?
reduce the chance of false identification.----apex
What is the difference between adodc and adodb?
The main difference between ADODC and ADODB is that whereas ADODB is a class library, ADODC is just but a data control. The other difference is that ADODC uses the system resources more compared to the ADODB.
What are the examples of normalization upto 3nf?
3rd normal form can remove transitive dependencies. for example, group city and group supervisor are depending on a non.key field group number.
What are the importance of computerized payroll system?
Computerized payroll systems are much faster and easier compared to the manual processing......
Also quick and accurate answers are produced by the computerized software
What are the primary role of technocrats and managers play in actualizing the data processing need?
What_are_the_primary_role_of_technocrats_and_managers_play_in_actualizing_the_data_processing_need
What are the disadvantages of data redundancy?
with data redundancy there willbe more wastage of memory space as same type of data willbe saved many times
when to want to see the data all duplicate results will come
What is one to many relationship in database er diagram?
A one-to-many relationship means that one row in one of the tables will relate directly to many rows in the other table.
What are the duties of a database administrator?
1. Designing of the database structure. This is by helping in determinig the design of the database information and contents.
2. He/She decide information contents of the database. Deciding the storage structure and acces strategy.
database is the collection of information that store in known procedure
What ACID stands in SQL Server?
ACID (an acronymn for Atomicity Consistency Isolation Durability) is a concept that Database Professionals generally look for when evaluating databases and application architectures. For a reliable database all this four attributes should be achieved. Atomicity is an all-or-none proposition. Consistency guarantees that a transaction never leaves your database in a half-finished state. Isolation keeps transactions separated from each other until they’re finished. Durability guarantees that the database will keep track of pending changes in such a way that the server can recover from an abnormal termination. Above four rules are very important for any developers dealing with databases. Ref: http://blog.sqlauthority.com/2007/12/09/sql-server-acid-atomicity-consistency-isolation-durability/ - ACID (atomicity, consistency, isolation, and durability) is an acronym and mnemonic device for learning and remembering the four primary attributes ensured to any transaction by a transaction manager (which is also called a transaction monitor). These attributes are: Atomicity. In a transaction involving two or more discrete pieces of information, either all of the pieces are committed or none are. Consistency. A transaction either creates a new and valid state of data, or, if any failure occurs, returns all data to its state before the transaction was started. Isolation. A transaction in process and not yet committed must remain isolated from any other transaction. Durability. Committed data is saved by the system such that, even in the event of a failure and system restart, the data is available in its correct state. The ACID concept is described in ISO/IEC 10026-1:1992 Section 4. Each of these attributes can be measured against a benchmark. In general, however, a transaction manager or monitor is designed to realize the ACID concept. In adistributed system, one way to achieve ACID is to use a two-phase commit(2PC), which ensures that all involved sites must commit to transaction completion or none do, and the transaction is rolled back (see rollback). Ref: http://searchsqlserver.techtarget.com/sDefinition/0,,sid87_gci213756,00.html
What is Primary file organization unordered?
Primary file organization is the way in which we determine how the file records are physically placed on the disk and hence, how the records can be accessed. Unordered means that there is no particular order in this way, i.e. a heap algorithm is used.
What does BP abbreviation stand for?
British Petroleum.
Technically it's an acronym not an abbreviation. An abbreviation is a shortened version of a word, such as abbr. for abbreviation. An acronym is any combination of abbreviations, contractions or initialisms. BP is an initialism and is therefore an acronym.
The relationships between users database applications DBMS and database?
The relationships between database applications DBMS and databases is as follows:
Databases can be simple or complex. simple databases can be kept in a Microsoft Excel spreadsheet or they can be maintained in a user generated Microsoft Access database which can be programmed to query certain data that has been entered into that database over a period of time. Microsoft Excel and Microsoft Access are also applications that are used to build databases that can be incorporated into DBMS or Database Management Systems. These systems can be extremely complex or they can be simple meaning that maintenance to these systems is not demanding. If the DBMS is complex it may require an entire team of technicians and in some cases engineers.The relationship between users, database applications, databases, and Database Management Systems can be simplified even further - Users can access a database that has been created with a database application to query managed data that is a part of a uniform Database management system.
What is the difference between database instance and relation schema?
Database Instance
The term instance is typically used to describe a complete database environment, including the RDBMS software, table structure, stored procedures and other functionality. It is most commonly used when administrators describe multiple
instances of the same database.Also Known As: environment
Examples: An organization with an employees database might have three different
instances: production (used to contain live data), pre-production (used to test new
functionality prior to release into production) and development (used by
database developers to create new functionality).
RELATION SCHEMA
A relation schema can be thought of as the basic information describing
a table or relation. This includes a set of column names, the data types associated
with each column, and the name associated with the entire table. For example, a
relation schema for the relation called Students could be expressed using the
following representation:
Students(sid: string, name: string, login:
string, age: integer, gpa: real)
There are five fields or columns, with names and types as shown above.
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 accessed by multiple users and by multiple application programs like (SQL Server, Oracle, Ms-Access) .
The advantages of DBMS
- It represents complex relationships among different data items.
- Keeps a tight control on data redundancy.
- Enforces user defined rules to ensure the integrity of data in a table form.
- Maintains data dictionary for the storage of information pertaining to data fields and data manipulation.
- Ensures that data can be shared across all applications.
- Enforces data access authorization.
- Has an automatic intelligent backup and recovery procedure of data.
- Has different interfaces through which users can manipulate data.
Advantages of using a DBMS
There are three main features of a database management system that make it attractive to use a DBMS in preference to more conventional software. These features are centralized data management, data independence, and systems integration.
In a database system, the data is managed by the DBMS and all access to the data is through the DBMS providing a key to effective data processing. This contrasts with conventional data processing systems where each application program has direct access to the data it reads or manipulates. In a conventional DP system, an organization is likely to have several files of related data that are processed by several different application programs.
In the conventional data processing application programs, the programs usually are based on a considerable knowledge of data structure and format. In such environment any change of data structure or format would require appropriate changes to the application programs. These changes could be as small as the following:
- Coding of some field is changed. For example, a null value that was coded as -1 is now coded as -9999.
- A new field is added to the records.
- The length of one of the fields is changed. For example, the maximum number of digits in a telephone number field or a postcode field needs to be changed.
- The field on which the file is sorted is changed.
If some major changes were to be made to the data, the application programs may need to be rewritten. In a database system, the database management system provides the interface between the application programs and the data. When changes are made to the data representation, the metadata maintained by the DBMS is changed but the DBMS continues to provide data to application programs in the previously used way. The DBMS handles the task of transformation of data wherever necessary.
This independence between the programs and the data is called data independence. Data independence is important because every time some change needs to be made to the data structure, the programs that were being used before the change would continue to work. To provide a high degree of data independence, a DBMS must include a sophisticated metadata management system.
In DBMS, all files are integrated into one system thus reducing redundancies and making data management more efficient. In addition, DBMS provides centralized control of the operational data. Some of the advantages of data independence, integration and centralized control are:
- Redundancies and inconsistencies can be reduced
In conventional data systems, an organisation often builds a collection of application programs often created by different programmers and requiring different components of the operational data of the organisation. The data in conventional data systems is often not centralised. Some applications may require data to be combined from several systems. These several systems could well have data that is redundant as well as inconsistent (that is, different copies of the same data may have different values). Data inconsistencies are often encoutered in everyday life. For example, we have all come across situations when a new address is communicated to an organisation that we deal with (e.g. a bank, or Telecom, or a gas company), we find that some of the communications from that organisation are recived at the new address while others continue to be mailed to the old address. Combining all the data in a database would involve reduction in redundancy as well as inconsistency. It also is likely to reduce the costs for collection, storage and updating of data.
- Better service to the Users
A DBMS is often used to provide better service to the users. In conventional systems, availability of information is often poor since it normally is difficult to obtain information that the existing systems were not designed for. Once several conventional systems are combined to form one centralised data base, the availability of information and its up-to-dateness is likely to improve since the data can now be shared and the DBMS makes it easy to respond to unforseen information requests.
Centralizing the data in a database also often means that users can obtain new and combined information that would have been impossible to obtain otherwise. Also, use of a DBMS should allow users that do not know programming to interact with the data more easily.
The ability to quickly obtain new and combined information is becoming increasingly important in an environment where various levels of governments are requiring organisations to provide more and more information about their activities. An organisation running a conventional data processing system would require new programs to be written (or the information compiled manually) to meet every new demand.
- Flexibility of the system is improved
Changes are often necessary to the contents of data stored in any system. These changes are more easily made in a database than in a conventional system in that these changes do not need to have any impact on application programs.
- Cost of developing and maintaining systems is lower
As noted earlier, it is much easier to respond to unforseen requests when the data is centralized in a database than when it is stored in conventional file systems. Although the initial cost of setting up of a database can be large, one normally expects the overall cost of setting up a database and developing and maintaining application programs to be lower than for similar service using conventional systems since the productivity of programmers can be substantially higher in using non-procedural languages that have been developed with modern DBMS than using procedural languages.
- Standards can be enforced
Since all access to the database must be through the DBMS, standards are easier to enforce. Standards may relate to the naming of the data, the format of the data, the structure of the data etc.
- Security can be improved
In conventional systems, applications are developed in an ad hoc manner. Often different system of an organisation would access different components of the operational data. In such an environment, enforcing security can be quite difficult.
Setting up of a database makes it easier to enforce security restrictions since the data is now centralized. It is easier to control who has access to what parts of the database. However, setting up a database can also make it easier for a determined person to breach security. We will discuss this in the next section.
- Integrity can be improved
Since the data of the organization using a database approach is centralized and would be used by a number of users at a time, it is essential to enforce integrity controls.
Integrity may be compromised in many ways. For example, someone may make a mistake in data input and the salary of a full-time employee may be input as $4,000 rather than $40,000. A student may be shown to have borrowed books but has no enrolment. Salary of a staff member in one department may be coming out of the budget of another department.
If a number of users are allowed to update the same data item at the same time, there is a possiblity that the result of the updates is not quite what was intended. For example, in an airline DBMS we could have a situation where the number of bookings made is larger than the capacity of the aircraft that is to be used for the flight. Controls therefore must be introduced to prevent such errors to occur because of concurrent updating activities. However, since all data is stored only once, it is often easier to maintain integrity than in conventional systems.
- Enterprise requirements can be identified
All enterprises have sections and departments and each of these units often consider the work of their unit as the most important and therefore consider their needs as the most important. Once a database has been set up with centralised control, it will be necessary to identify enterprise requirements and to balance the needs of competing units. It may become necessary to ignore some requests for information if they conflict with higher priority needs of the enterprise.
- Data model must be developed
Perhaps the most imporrant advantage of setting up a database system is the requirement that an overall data model for the enterprise be built. In conventional systems, it is more likely that files will be designed as needs of particular applications demand. The overall view is often not considered. Building an overall view of the enterprise data, although often an expensive exercise, is usually very cost-effective in the long term.
it is a set one or more attribute,that taken collectively allow as to idendify uniquly and entity in entity set.
ex-customer-id,
