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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
Explain the concept of foreign key How a foreign key differs from a primary key?
Foreign keys are used to link one database with another. A primary key is an attribute of a record that allows users to identify information.
What are the reasons for limiting the size of a field in a database?
A reason to limit the amount of data any field contains can vary greatly, but common reason is to standardise the data. One of the principle behind databases is to create collections of data that can be organized into standard format to make it easier to create information for reporting or analysis.
Disadvantages of a file management system?
Traditional file management lacks in may ways from DBMS we use today.1) Traditional FPS does not maintain data integrity.
2) Traditional FPS does not maintain data consistency.
3) Traditional FPS does not support and allow to use query .
Advantages and disadvantages of multimedia databases?
Advantages of multimedia databases include that it is easy to use, makes lectures more interesting, and it is visually appealing. Some disadvantages of multimedia databases include the expense, and the fact that they are not always easy to configure.
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They are easy to use if designed to be so - including robust error-traps so for example the programmes does not crash from an incorrectly-typed admin entry (yes, I've battled with commercially-made rubbish that did just that). To design and write a proper, complex, database is never easy unless you have a great deal of skill and experience in them - and therein lies the root of many software problems from the users' point of view. The programmer knows the application intimately, down to language level, machine-code even; can run its most arcane routines without thinking; so cannot see why he or she has given the "shop-floor" staff an utter nightmare to use!
What is Primary file organization?
primary file organization says that how data itself is stored on the storage device.
a secondary logical maintinance of physically stored data that helps us to speed access to the physically stored data.
Which is the first uml diagram drawn while designing a system?
Which UML diagram is drawn first depends on the software design process, system analysed or designed, etc.
If you start by collecting requirements, your first diagrams will be use case diagrams.
If you start by existing system analysis, it could be class diagrams of domain model.
If you create some services, you might start with component diagrams.
If your system is in specific domain, you might start with profile diagrams...
What is database organization?
A database organization is exactly what it sounds like. This is a database that is organized in some way, shape, or form.
What is the difference between T-sql and sql?
T-SQL is Microsoft's version of the generic SQL langauge to be used with, for example, Microsoft SQL Server.
Describe the Data Mining Functions Data Mining Techniques?
Data mining refers to the broadly-defined set of techniques involving finding meaningful patterns - or information - in large amounts of raw data.
At a very high level, data mining is performed in the following stages (note that terminology and steps taken in the data mining process varies by data mining practitioner):
1. Data collection: gathering the input data you intend to analyze
2. Data scrubbing: removing missing records, filling in missing values where appropriate
3. Pre-testing: determining which variables might be important for inclusion during the analysis stage
4. Analysis/Training: analyzing the input data to look for patterns
5. Model building: drawing conclusions from the analysis phase and determining a mathematical model to be applied to future sets of input data
6. Application: applying the model to new data sets to find meaningful patterns
Data mining can be used to classify or cluster data into groups or to predict likely future outcomes based upon a set of input variables/data.
Common data mining techniques and tools include, for example:
a. decision tree learning
b. Bayesian classification
c. neural networks
During the analysis phase (sometimes also called the training phase), it is customary to set aside some of the input data so that it can be used to cross-validate and test the model, respectively. This is an important step taken in order to to avoid "over-fitting" the model to the original data set used to train the model, which would make it less applicable to real-world applications.
How much redundancy pay will you get after 2 years?
Probably not much 2 weeks per year....4 weeks max maybe.
Example for joining more than 3 tables using SQL server?
select a.name, b.id, c. product
from user a
left outer join activities b
on a.user_id = b.user_id
left outer join products c
on b.product_id = c. pproduct_id
How to draw entity relationship diagram?
To draw a relationship diagram, start by placing relationship at the center of the paper. Connect entities to the relationship, and branch out with the different attributes.
List at least 3 main differences between Mircosoft SQL Server and Microsoft Access?
MYSQL is for the back end of applications, where as Microsoft access is for relational databases and such.
MYSQL can be used in conjuntion with server side scripting languages where as access cannot
access cannot import mysql data where as mysql can import data from other programs, if used correctly you will have a functional database based on what data is imported throught (exel,access ect)
What is computer primary keys?
Primary keys are used in databases to uniquely identify records. No two records can have the same primary key. This means that there is a way of distinguishing records that have similar details, like if you have a database with lots of names and there are some people in it who have the same name. Every record must have a primary key. It cannot be left blank, because it is needed to identify each record. Primary keys are also important in relational databases when relationships are being built between tables. A record in one table can refer to the primary key in another to establish the link to the correct record.
Why you would create a database?
Database is created to keep a systematic record of data of a particular field.
Clustering is when two or more servers are linked together with the Network Load Balancing protocol (in Windows) to allow for faster response time and reliability. This way, if one server goes down, another can pick up the slack without any interuption in network performance - in theory anyway! :-)
The word clustering means alot of numbers (:
What are the inference rules for functional dependency?
"The present list of 19 rules of inference constitutes a COMPLETE system of truth-functional logic, in the sense that it permits the construction of a formal proof of validity for ANY valid truth-functional argument." (FN1)
The first nine rules of the list are rules of inference that "correspond to elementary argument forms whose validity is easily established by truth tables." (Id, page 351). The remaining ten rules are the Rules of Replacement, "which permits us to infer from any statement the result of replacing any component of that statement by any other statement logically equivalent to the component replaced." (Id, page 359).
Here are the 19 Rules of Inference:
1. Modus Ponens (M.P.)
p q
p
q 2.Modus Tollens (M.T.)
p q
~q
~p 3.Hypothetical Syllogism (H.S.)p q
q r
p r 4.Disjunctive Syllogism (D.S.)p v q
~ p
q 5. Constructive Dilemma (C.D.)(p q) . (r s)
p v r
q v s 6. Absorption (Abs.)p q
p (p. q)
7. Simplification (Simp.)p . q
p 8. Conjunction (Conj.)p
q
p . q 9. Addition (Add.)p
p v q
Any of the following logically equivalent expressions can replace each other wherever they occur:
10.De Morgan's Theorem (De M.) ~(p . q) (~p v ~q)
~(p v q) (~p . ~q) 11. Commutation (Com.)(p v q) (q v p)
(p . q) (q . p) 12. Association (Assoc.)[p v (q v r)] [(p v q) v r]
[p . (q . r)] [(p . q) . r] 13.Distribution (Dist) [p . (q v r)] [(p . q) v (p . r)]
[p v (q . r)] [(p v q) . (p v r)] 14.Double Negation (D.N.)p ~ ~p 15. Transposition (Trans.)(p q) (~q ~p) 16. Material Implication (M. Imp.)(p q) (~p v q) 17. Material Equivalence (M. Equiv.)(p q) [(p q) . (q p)]
(p q) [(p . q) v (~p . ~q)] 18. Exportation (Exp.)[(p . q) r] [p (q r)] 19. Tautology (Taut.) p (p v p)
p (p . p)
FN1: Introduction to Logic, Irving M. Copi and Carl Cohen, Prentice Hall, Eleventh Edition, 2001, page 361. The book contains the following footnote after this paragraph: "A method of proving this kind of completeness for a set of rules of inference can be found in I. M. Copi, Symbolic Logic, 5th Edition. (New York: Macmillian, 1979), chap 8, See also John A. Winnie, "The Completeness of Copi's System of Natural Deduction," Notre Dame Journal of Formal Logic 11 (July 1970), 379-382."
How many types of normal forms?
The formal classifications describing the level of database normalization in a data model are called Normal Forms (NF) and the process of doing this is Normalization.
First normal form
First normal form (1NF) lays the groundwork for an organised database design:
Ensure that each table has a primary key: minimal set of attributes which can uniquely identify a record.
Eliminate repeating groups (categories of data which would seem to be required a different number of times on different records) by defining keyed and non-keyed attributes appropriately.
Atomicity: Each attribute must contain a single value, not a set of values.
'First normal form' depends on functional dependency formula f(x)=y. For every value of x there is value for y.
Second normal form
Second normal form (2NF) If a table has a composite key, all attributes must be related to the whole key:
The database must meet all the requirements of the first normal form.
The relational schema should not have any partial functional dependency i.e. No proper subset of the primary key should derive a functional dependency belonging to the same schema. For example, consider functional dependencies FD:{AB->C, A->D, C->D} here AB is the primary key, as A->D this relational schema is not in 2NF.
Third normal form
Third normal form (3NF) requires that data stored in a table be dependent only on the primary key, and not on any other field in the table.
The database must meet all the requirements of the first and second normal form.
All fields must be directly dependent on the primary key field. Any field which is dependent on a non-key field which is in turn dependent on the Primary Key (ie a transitive dependency) is moved out to a separate database table.
4 FOURTH AND FIFTH NORMAL FORMS
Fourth [5] and fifth [6] normal forms deal with multi-valued facts. The multi-valued fact may correspond to a many-to-many relationship,
4.1 Fourth Normal Form
Under fourth normal form, a record type should not contain two or more independent multi-valued facts about an entity. In addition, the record must satisfy third normal form.
Fifth normal form deals with cases where information can be reconstructed from smaller pieces of information that can be maintained with less redundancy. Second, third, and fourth normal forms also serve this purpose, but fifth normal form generalizes to cases not covered by the others.
Boyce-Codd normal form
Boyce-Codd normal form (or BCNF) requires that there be no non-trivial functional dependencies of attributes on something other than a superset of a candidate key (called a superkey).
Types of databases in sql server 2005?
Types of Database in sql server 2005:-
1.Master Database
2.Tempdb Database
3.Model Database
4.MSDB Database
5.Resource Database
What does primary key mean in database form?
In a Database, more specifically a relational model, columns of one table that relate to columns of another table are called "key columns".
There are two types of "key" columns. Foreign key and Primary Key.
The Primary key of a table is usually a column within a table that contains unique data which cannot be duplicated. Think of it as a "unique identifier" column. You can actually create an array of key columns in a table to represent a unique series of values as well. (so PKey 1,2,3 are unique and no group of PKey's 1,2,3 will be the same, even though sometimes any one of those columns may contain a single value that has been duplicated, the consolidated value of all 3 will never be replicated).
The Primary key of table A is linked to the Primary key of Table B for instance. Table B's Primary Key in this relationship is then called a "Foreign Key", meaning "The Primary Key of the OTHER table".
That's a pretty basic understanding of how they work. There is a little bit more involved but this is the gist of it.
A primary characteristic that distinguishes not-for-profit entities from business entities is?
the importance of the budget in the governing process.
List two reasons why null values might be introducedin database?
1. special requirements for its use in SQL joins.
2. special handling required by aggregate functions and SQL grouping operators
