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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
How is concept of functional dependency associate with process of normalization?
Functional dependency is a key concept in database normalization, as it defines the relationship between attributes in a relation. It indicates that the value of one attribute (or a group of attributes) uniquely determines the value of another attribute. Normalization utilizes these dependencies to organize data efficiently, eliminating redundancy and minimizing the potential for update anomalies. By identifying and enforcing functional dependencies, databases can be structured in a way that enhances data integrity and reduces duplication.
What are the Advantages of a data projector to a teacher?
what are the advantages of a data projector
What is weak entity sets in dbms?
An entity set may not have sufficient attributes to form a primary key is called weak entity set. One with primary key is called strong entity set.
What are the advantages of menu-driven system?
ADVANTAGES
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Most end-users are quite familiar with using menus to issue commands to a program.
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Menu's are a convenient way to bundle related common commands, i.e., under a single main menu. This allows a programmer to create a separate module for each type of menu functionality.
Menu-driven programs are especially good for mobile devices, due to therr small user interface and input/access controls.
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A large program should be developed incrementally, i.e. in small steps. The overall program logic consisting of major sub-tasks is designed first without the need to know the details of how these sub-tasks will be performed. Menu driven programs are particularly well suited for incremental development. Once the main logic is written, ``dummy'' functions (sometimes called stubs) can be written for each task which may do nothing but print a debug message to the screen. Then each sub-task is implemented and tested one at a time. Only after some of the basic sub-tasks are implemented and tested, should others be implemented.
At any given time during program development, many sub-task functions may not yet be implemented. For example, we may first implement only get data, print data, and help ( help is easy to implement; it just prints the menu). Other sub-tasks may be delayed for later implementation These stub-procedures (place-holders) are in skeleton form and can be modified as needed without changing the main program logic. In programming languages like C or C++, it should be noted that the linker will require that all functions used in the driver be defined. The stubs satisfy the linker without having to write the complete function until later.
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A menu needs to be useable. Let's take the example of database program. A menu is, in effect, a conceptual mold of what is happening to the database. In this respect, the menu system needs to be easily understood. It needs to be represented as a complete system that is neither overtly complex nor monotonous for the end user.
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A menu-driven program is normally easier to use than a command-driven program, particularly for those not particularly well expeirenced in computer usage.
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Almost all programs on the market have standard features which include menu-driven interfaces.
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As a rule, menu-driven systems are easier for the inexperienced user to learn, whereas, command-driven systems do not slow down experienced users who already know the necessary choices. Most new users cannot remember commands like "T/B4/BN4/C5/E5:C5/D5:B4/C5;". In a non-Windows environment, experienced users may not want to wait while the program printss a menu of familiar choices. This situation occurs where the menu choices are displayed as an actual list, and not as a Windows drop-down menu. Although most programs use only either a menu-driven or a command-driven approach, the best ones provide menus for new users, and let experienced users avoid the menus once they have learned the necessary commands.
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DISADVANTAGES?
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Because menu-driven programs usually have redundant ways of doing things, you may have to do extra coding, i.e., synchronize the menu items' states with that of their counter-parts on the toolbar or context menu. You must also show, hide, disable, check, uncheck the menu items where appropriate. Some menu items are dynamically created, i.e., recently view documents. This requires additional coding.
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If the programmer does not take care—or is overly ambitious—a menu can easily become too cluttered if an abundance of selections is available for the user. Furthermore, depending upon the size and resolution of the display, if the menu is an in-place one (versus a drop-down menu), it could occupy too much screen space, hindering the area available for actual program display. This situation can especially arise in a non-Windows program. On the other hand, putting too few items on a menu will bring about unnecessary delays switching between menus, further causing the work to be both repetitive and tedious.
Menus can end up having too many commands or sub-menus or sub-sub-menus
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When does the product functionality stop and the preference of the user begin? In the interest of making a menu functional, the user needs to be comfortable with the options that are available. What the project calls for, and what the user wants,can be two different agendas. In designing a menu, it must be both functionable from a programming standpoint and easy to navigate for the end user.
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Even among menu-driven systems, there can be important differences.Some programs require that you first move a highlight bar onto your chosen command in the list by either pressing the cursor control keys or moving the mouse. Such programs let you press a key (typically the
Other programs let you press just the first letter of the command you want reardless of which choice is highlighted, and without having to press anything else. that approach to menu-drive system saves keystrokes; and, in the long run, it can increase the user's speed in command entry considerably.
One way to speed up command entry is by storing commonly used commands in macros, which are abbreviated keystroke sequence that substitute longer text strings in their place. By assigning a lengthy command string to a macro, you can then type the shorter macro each time you want to use the longer command string.
In model ER why you need DBMS system?
Because it is very useful in mapping the meanings and interactions of real-world enterprises onto a conceptual schema. Because of this usefulness, many database-design tools draw on concepts from the ER-model. The ER data model employs three basic notation:
a.) Entity sets
b.) Relationship sets
c.) Attributes.
Difference between alter and update commands in sql?
Update and Alter are two SQL (Structured Query Language) commands used for modifying databases. Update statement is used to update existing records in a database. Update is a Data Manipulation Language (DML) statement. Alter SQL command is used to modify, delete or add a column to an existing table in a database. Alter is a Data Definition Language (DDL) statement.Commands that are used to define the structure of a database (database schema) are called DDL statements.
Sequence of triggers firing in oracle forms?
Trigger Firing sequence:
Order as follows
First Logon Triggers are fired
1.PRE-LOGON
2.ON-LOGON
3.POST-LOGON
After that Pre Triggers
4. PRE-FORM
5. PRE-BLOCK
6. PRE-TEXT
After that WHEN-NEW Triggers
7. WHEN-NEW-FORM-INSTANCE
8. WHEN-NEW-BLOCK-INSTANCE
9. WHEN-NEW-ITEM-INSTANCE
After that ITEM Level Triggers
After this focus is on the first item of the Block. If you type some data and press the tab key following trigger will fire in sequence
10.KEY-NEXT-ITEM (This trigger is present on the item level).
11.POST-CHANGE (This trigger is present on the item level).
12.WHEN-VALIDATE-ITEM (This trigger is present on the item level).
13.POST-TEXT-ITEM (This trigger is present on the item level).
14.WHEN-NEW-ITEM-INSTANCE (Block Level Trigger).
Now focus will go the next item present on the form.
If there are no further items present on the screen them if we enter data and press tab key then only KEY-NEXT-ITEM is fired. Now suppose we close the form then the item level triggers are fired.
POST TRIGGERS
15.POST-BLOCK
16.POST-FORM
Now the form will be closed.
What is a partial dependency in normalization in dbms?
I guess you will just have to google it my friend..
Yours Faithfully
Gedz
What are the basic components of a database?
Tables, Entities, Attributes, Primary Keys, and Foreign Keys
What is the most common type of relationship you will encounter between tables?
one-to-many relationships
What is non trivial functional dependency?
-->non trivial functional dependency is totally opposite to the trivial functional dependency.
--> non trivial dependency means X-->Y that is if Y is not proper subset of X table or relation with X then it said to be non trivial functional dependency.
1st to 5th normalization form in database?
the inventor of the relational model, introduced the concept of normalization and what we now know as the First Normal Form (1NF) in 1970.[1] Codd went on to define the Second Normal Form (2NF) and Third Normal Form (3NF) in 1971,[2] and Codd and Raymond F. Boyce defined the Boyce-Codd Normal Form (BCNF) in 1974.[3] Informally, a relational database table is often described as "normalized" if it is in the Third Normal Form.[4] Most 3NF tables are free of insertion, update, and deletion anomalies.
How do you stop double logging in using PHP and MySQL?
Assuming you are using a User database and sessions, simply add a Session key. Auto generate this key as follows:
$newsession_key = SHA1( RAND(100000000,999999999));
Enter this in the database on the user row when logging in and store it in a session and in the database. Then on your code where you define the user logged in status you add something like:
$database_session = $DATABASE['sessionkey'];
If($database_session != $_SESSION['sessionkey']){
Unset($_SESSION['username'],$_SESSION['password'],$_SESSION['sessionkey']); #A*
}
A* Add in any sessions you use to keep the user logged in.
Difference between activity diagram and dfd?
In data flow diagrams, the lines between "boxes" represent data that flows between components of a system. Because these only show the flow of data, they do not give an indication of sequencing.
In activity diagrams, those lines are simply transitions between activities and do not represent data flow at all. They more represent the sequencing of activities and decisions. You can tell from these what order things happen in.
Explain how the supertype and subtype entities are transformed into tables?
Data design can incorporate supertype and subtype tables in the document. In the flow chart, the organization will determine the order and usefulness of each type.
i have no idea at all. Hate this subject.
Discuss the advantages and disadvantages of conventional database management systems?
Advantages -- many already exist;
good for simple applications;
very
efficient efficient
Disadvantages -- data duplication;
hard to evolve;
hard to build for
complex complex applications applications
data transaction language
data transaction languagedata transaction language data transaction language
data transaction language
The Entity-Relationship Model is often referred to as a
semantic data model, because it more closely resembles real
world scenarios than, e.g., the relational model.
. In the ER model, we model the concept of "Instructors."
In the relational model we deal with names and phone
numbers.
. In the ER model, there is a distinction between entities
(objects) and relationships between such entities.
In the relational model, both concepts are represented by
relations.
Difference between loss systems and delay system?
1) In a loss system overload traffic is rejected without being serviced. In a delay system overload traffic is held in queue until the facilities become available to service it.
2)conventional circuit switching operates as a loss system since excess traffic is blocked and not serviced without a retry on the part of the user. Store-and-forward message or packet switching obviously posses the basic characteristics of a delay system
3)The basic measure of performance for a loss system is the probability of rejection(blocking probability). A delay system on the other hand is measured in terms of service delays.
Difference in transaction management in centralized and distributed system?
Centralized computing is computing done at a central location, using terminals that are attached to a central computer. The computer itself may control all the peripherals directly (if they are physically connected to the central computer), or they may be attached via a terminal server. Alternatively, if the terminals have the capability, they may be able to connect to the central computer over the network. The terminals may be text terminals or thin clients, for example.
