All Versions of Android

Cupcake:

• Android 1.5

Donut:

• Android 1.6

Eclair:

• Android 2.0
• Android 2.1

Froyo: 

• Android 2.2

Gingerbread:

• Android 2.3

Honeycomb:

• Android 3.0
• Android 3.1
• Android 3.2

Ice Cream Sandwich:

• Android 4.0

Jelly Bean:

• Android 4.1
• Android 4.2
• Android 4.3

KitKat:

• Android 4.4

Lollipop:

• Android 5.0
• Android 5.1

Marshmallow:

• Android 6.0

" What happens on the web in 30 seconds ! "

" What happens on the web in 30 seconds ! "
.
-20,400 GB of global IP data transferred.
-70+ BotNet Infections.
-12 New victims of identity theft.
-3+ New Wikipedia Articles published.
-102 Million Emails sent.
-700 new Mobile Users.
-25.000 App downloads.
-$45,000 sales on Amazon.
-31,141 hours of music played on Pandora.
-55+ New linked in Accounts.
-Over 10 Millions photo.
-Views, 3500+ Photo uploads on Flickr.
-165 + New Twitter accounts, 50,000+ New
Tweets.
-150,000 Facebook Log ins.
3M+ Facebook Views ,
350,000 Status update,
40,000+ Wall posts,

The Diffrence between DDoS and DoS Attack

The Diffrence between Ddos and Dos ------------------------------------- DoS A DoS Attack is a Denial of Service attack. This meens that one computer and one internet connection is used to flood a server with packets (TCP / UDP). The point of such a denial of service attack is to overload the targeted servers bandwidth and other resources. This will make the server inaccessible to others and blocking the website or whatever else is hosted there. DDoS A DDoS Attack is a Distributed Denial of Service Attack. In most respects it is similar to a DoS attack but the results are much different. Instead of one computer and one internet connection the DDoS attack utilises many computers and many connections. The computers behind such an attack are often distributed around the whole world and will be part of what is known as a botnet. The main difference between a DDoS attack vs a DoS attack, therefore, is that the target server will be overload by hundreds or even thousands of requests in the case of the former as opposed to just one attacker in the case of the latter. 

If you want to be security professional even hacker you should know these terms , u may know or not i just share with you 

1.Adware - Adware is software designed to force pre-chosen ads to display on your system. Some adware is designed to be malicious and will pop up ads with such speed and frequency that they seem to be taking over everything, slowing down your system and tying up all of your system resources. When adware is coupled with spyware, it can be a frustrating ride, to say the beast. 

2.Back Door - A back door is a point of entry that circumvents normal security and can be used by a cracker to access a network or computer system. Usually back doors are created by system developers as shortcuts to speed access through security during the development stage and then are overlooked and never properly removed during final implementation. Sometimes crackers will create their own back door to a system by using a virus or a Trojan to set it up, thereby allowing them future access at their leisure. 

3.Black Hat - Just like in the old westerns, these are the bad guys. A black hat is a cracker. To add insult to injury, black hats may also share information about the “break in” with other black hat crackers so they can exploit the same vulnerabilities before the victim becomes aware and takes appropriate measures… like calling Global Digital Forensics! 

4. Bot - A bot is a software “robot” that performs an extensive set of automated tasks on its own. Search engines like Google use bots, also known as spiders, to crawl through websites in order to scan through all of your pages. In these cases bots are not meant to interfere with a user, but are employed in an effort to index sites for the purpose of ranking them accordingly for appropriate returns on search queries. But when black hats use a bot, they can perform an extensive set of destructive tasks, as well as introduce many forms of malware to your system or network. They can also be used by black hats to coordinate attacks by controlling botnets. 

5. Botnet – A botnet is a network of zombie drones under the control of a black hat. When black hats are launching a Distributed Denial of Service attack for instance, they will use a botnet under their control to accomplish it. Most often, the users of the systems will not even know they are involved or that their system resources are being used to carry out DDOS attacks or for spamming. It not only helps cover the black hat’s tracks, but increases the ferocity of the attack by using the resources of many computer systems in a coordinated effort. 

6. Cookies – A cookie is a small packet of information from a visited webserver stored on your system by your computer’s browser. It is designed to store personalized information in order to customize your next visit. For instance, if you visit a site with forms to fill out on each visit, that information can be stored on your system as a cookie so you don’t have to go through the process of filling out the forms each time you visit. 

7. Cracker - When you hear the word hacker today, in reality it is normally referring to a cracker, but the two have become synonymous. With its origin derived from “safe-cracker” as a way to differentiate from the various uses of “hacker” in the cyber world, a cracker is someone who breaks into a computer system or network without authorization and with the intention of doing damage. A cracker may destroy files, steal personal information like credit card numbers or client data, infect the system with a virus, or undertake many others things that cause harm. This glossary will give you an idea of what they can do and some of the means they use to achieve their malicious objectives. These are the black hats. 

8. Denial of Service Attack (DOS) – A Denial of Service attack is an attack designed to overwhelm atargeted website to the point of crashing it or making it inaccessible. Along with sheer numbers and frequency, sometimes the data packets that aresent are malformed to further stress the system trying to process the server requests. A successful Denial of Service attack can cripple any entity that relies on its online presence by rendering their website virtually useless. 

9. Distributed Denial of Service Attack (DDOS) - A Distributed Denial of Service attack is done with thehelp of zombie drones (also known as a botnet) under the control of black hats using a master program to command them to send information anddata packets to the targeted webserver from the multiple systems under their control. This obviously makes the Distributed Denial of Service attack even more devastating than a Denial of Service attack launched from a single system, flooding the target server with a speed and volume that is exponentially magnified. As is normally the case with zombie drones and botnets, this is often done without the user of the controlled system even knowing they were involved. 

10. Dumpster Diving - The act of rummaging through the trash of an individual or business to gather information that could be useful for a cyber criminal to gain access to a system or attain personal information to aid them in identity theft or system intrusion. One person’s garbage can indeed be a cyber criminal’s treasure. 

11.Easter Egg - A non-malicious surprise contained in a program or on a circuit board installed by the developer. It could be as simple as a text greeting, a signature, or an image embedded on a circuit board,or comprise a more complex routine, like a video or a small program. The criteria that must be met to be considered an Easter Egg are that it be undocumented, non-malicious, reproducible to anyone with the same device or software, not be obvious, and above all – it should be entertaining! 

12.Firewall - A firewall is a security barrier designed to keep unwanted intruders “outside” a computer system or network while allowing safe communication between systems and users on the “inside” of the firewall. Firewalls can be physical devices or software-based,or a combination of the two. A well designed and implemented firewall is a must to ensure safe communications and network access and should be regularly checked and updated to ensure continued function. Black hats learn new tricks and exploit new techniques all the time, and what worked to keep them out yesterday may need to be adjusted or replaced over time. 

13.Gray Hat – A gray hat, as you would imagine, is a bit of a white hat/black hat hybrid. Thankfully, like white hats, their mission is not to do damage to a system or network, but to expose flaws in system security. The black hat part of the mix is that they may very well use illegal means to gain access to the targeted system or network, but not for the purpose of damaging or destroying data: they want to expose the security weaknesses of a particular system and then notify the “victim” of their success. Often this is done with the intent of then selling their services to help correct the security failure so black hats can not gain entry and/or access for more devious and harmful purposes. 

Full form of computer related terms:

Full form of computer related terms:

Full form of computer related terms:
* HTTP - Hyper Text Transfer Protocol.
* HTTPS - Hyper Text Transfer Protocol Secure.
* IP - Internet Protocol.
* URL - Uniform Resource Locator.
* USB - Universal Serial Bus.
* VIRUS - Vital Information Resource Under Seized.
* 3G - 3rd Generation.
* GSM - Global System for Mobile Communication.
* CDMA - Code Divison Multiple Access.
* UMTS - Universal Mobile Telecommunication System.
* SIM - Subscriber Identity Module.
* AVI = Audio Video Interleave
* RTS = Real Time Streaming
* SIS = Symbian OS Installer File
* AMR = Adaptive Multi-Rate Codec
* JAD = Java Application Descriptor
* JAR = Java Archive
* JAD = Java Application Descriptor
* 3GPP = 3rd Generation Partnership Project
* 3GP = 3rd Generation Project
* MP3 = MPEG player lll
* MP4 = MPEG-4 video file
* AAC = Advanced Audio Coding
* GIF = Graphic InterchangeableFormat
* JPEG = Joint Photographic ExpertGroup
* BMP = Bitmap
* SWF = Shock Wave Flash
* WMV = Windows Media Video
* WMA = Windows Media Audio
* WAV = Waveform Audio
* PNG = Portable Network Graphics
* DOC = Document (Microsoft Corporation)
* PDF = Portable Document Format
* M3G = Mobile 3D Graphics
* M4A = MPEG-4 Audio File
* NTH = Nokia Theme (series 40)
* THM = Themes (Sony Ericsson)
* MMF = Synthetic Music Mobile Application File
* NRT = Nokia Ringtone
* XMF = Extensible Music File
* WBMP = Wireless Bitmap Image
* DVX = DivX Video
* HTML = Hyper Text Markup Language
* WML = Wireless Markup Language
* CD - Compact Disk.
* DVD - Digital Versatile Disk.
* CRT - Cathode Ray Tube.
* DAT - Digital Audio Tape.
* DOS - Disk Operating System.
* GUI - Graphical User Interface.
* HTTP - Hyper Text Transfer Protocol.
* IP - Internet Protocol.
* ISP - Internet Service Provider.
* TCP - Transmission Control Protocol.
* UPS - UninterruptiblePower Supply.
* HSDPA - High Speed Downlink Packet Access.
* EDGE - Enhanced Data Rate for GSM [Global System for MobileCommunication] Evolution.
* VHF - Very High Frequency.
* UHF - Ultra High Frequency.
* GPRS - General Packet Radio Service.
* WAP - Wireless Application Protocol.
* TCP - Transmission Control Protocol .
* ARPANET - Advanced Research Project Agency  Network.
* IBM - International Business Machines.
* HP - Hewlett Packard.
* AM/FM - Amplitude/ Frequency Modulation.
* WLAN - Wireless Local Area Network

How safe is your password?

How safe is your password?

The first step in protecting your online privacy is creating a safe password - i.e. one that a computer program or persistent individual won't easily be able to guess in a short period of time. To help you choose a secure password, we've created a feature that lets you know visually how safe your password is as soon as you create it.

Tips for creating a secure password:

Include punctuation marks and/or numbers.

Mix capital and lowercase letters.

Include similar looking substitutions, such as the number zero for the letter 'O' or '$' for the letter 'S'.

Create a unique acronym.

Include phonetic replacements, such as 'Luv 2 Laf' for 'Love to Laugh'.

Things to avoid:

Don't reuse passwords for multiple important accounts, such as Gmail and online banking.

Don't use a password that is listed as an example of how to pick a good password.

Don't use a password that contains personal information (name, birth date, etc.)

Don't use words or acronyms that can be found in a dictionary.

Don't use keyboard patterns (asdf) or sequential numbers (1234).

Don't make your password all numbers, uppercase letters or lowercase letters.

Don't use repeating characters (aa11).

Tips for keeping your password secure:

Never tell your password to anyone (this includes significant others, roommates, parrots, etc.).

Never write your password down.

Never send your password by email.

Periodically test your current password and change it to a new one.

DBMS Questions(81-90)

81. Which date function is used to find the difference between two dates?

datediff

for Eg: select datediff (dd,'2-06-2007','7-06-2007') output is 5

82..What are the different phases of transaction?

Different phases are

Analysisphase

RedoPhase

Undophase

83. What do you mean by flat file database?

It is a database in which there are no programs or user access languages. It has no cross-filed capabilities but is user-friendly and provides user-interface management.

84... What is a query?

A query with respect to DBMS relates to user commands that are used to interact with a data base. The query language can be classified into data definition language and data manipulation language.

85. What do you mean by Correlated subquery?

Sub queries, or nested queries, are used to bring back a set of rows to be used by the parent query. Depending on how the subquery is written, it can be executed once for the parent query or it can be executed once for each row returned by the parent query. If the subquery is executed for each row of the parent, this is called a correlated subquery. A correlated subquery can be easily identified if it contains any references to the parent

subquery columns in its WHERE clause. Columns from the subquery cannot be referenced anywhere else in the parent query. The following example demonstrates a non-correlated subquery.

E.g. Select * From CUST Where '10/03/1990' IN (Select ODATE From ORDER Where CUST.CNUM = ORDER.CNUM)

86. What are the primitive operations common to all record management systems?

Addition,

deletion

modification.

87. Name the buffer in which all the commands that are typed in are stored

‘Edit’ Buffer

88. What are the unary operations in Relational Algebra?

PROJECTION

SELECTION.

89. Are the resulting relations of PRODUCT and JOIN operation the same?

No.

PRODUCT: Concatenation of every row in one relation with every row in another.

JOIN: Concatenation of rows from one relation and related rows from another.

90.What is RDBMS KERNEL?

Two important pieces of RDBMS architecture are the kernel, which is the software, and the data dictionary, which consists of the system-level data structures used by the kernel to manage the database You might think of an RDBMS as an operating system (or set of subsystems), designed specifically for controlling data access; its primary functions are storing, retrieving, and securing data. An RDBMS maintains its own list of authorized users and their associated privileges; manages memory caches and paging; controls locking for concurrent resource usage; dispatches and schedules user requests; and manages space usage within its table-space structures

DBMS Questions(71-80)

71.What is the difference between SQL and SQL Server ?

SQLServer is an RDBMS just like oracle,DB2 from Microsoft whereas Structured Query Language (SQL), pronounced "sequel", is a language that provides an interface to relational database systems. It was developed by IBM in the 1970s for use in System R. SQL is a de facto standard, as well as an ISO and ANSI standard.

SQL is used to perform various operations on RDBMS.

72.What is difference between Co-related sub query and nested sub query?

Correlated sub query runs once for each row selected by the outer query. It contains a reference to a value from the row selected by the outer query. Nested sub query runs only once for the entire nesting (outer) query. It does not contain any reference to the outer query row. For example,

Correlated Sub query:

select e1.empname, e1.basicsal, e1.deptno from emp e1 where e1.basicsal = (select max(basicsal) from emp e2 where e2.deptno = e1.deptno)

Nested Sub query:

select empname, basicsal, deptno from emp where (deptno, basicsal) in (select deptno, max(basicsal) from emp group by deptno)

73.WHAT OPERATOR PERFORMS PATTERN MATCHING?

Pattern matching operator is LIKE and it has to used with two attributes

1. % and

2. _ ( underscore )

% means matches zero or more characters and under score means mathing exactly one character

74)What is difference between Oracle and MS Access?

Oracle's features for distributed transactions, materialized views and replication are not available with MS Access. These features enable Oracle to efficiently store data for multinational companies across the globe. Also these features increase scalability of applications based on Oracle

75) What are disadvantages in Oracle and MS Access?

Oracle's features for distributed transactions, materialized views and replication are not available with MS Access. These features enable Oracle to efficiently store data for multinational companies across the globe. Also these features increase scalability of applications based on Oracle

76) What are features & advantages in Oracle and MS Access?

Oracle's features for distributed transactions, materialized views and replication are not available with MS Access. These features enable Oracle to efficiently store data for multinational companies across the globe. Also these features increase scalability of applications based on Oracle.

77.What is cluster. Cluster index and non cluster index ?

Clustered Index:- A Clustered index is a special type of index that reorders the way records in the table are physically stored. Therefore table may have only one clustered index. on-Clustered Index:- A Non-Clustered index is a special type of index in which the logical order of the index does not match the physical stored order of the rows in the disk. The leaf nodes of a non-clustered index does not consists of the data pages. instead the leaf node contains index rows.

78.How can i hide a particular table name of our schema?

you can hide the table name by creating synonyms. e.g) you can create a synonym y for table x create synonym y for x;

79.What is difference between DBMS and RDBMS?

The main difference of DBMS & RDBMS is

RDBMS have Normalization. Normalization means to refining the redundant and maintain the stabilization.

the DBMS hasn't normalization concept.

80.What are the advantages and disadvantages of primary key and foreign key in SQL?

Primary key Advantages

1) It is a unique key on which all the other candidate keys are functionally dependent

Disadvantage

1) There can be more than one keys on which all the other attributes are dependent on.

Foreign Key Advantage

1)It allows referencing another table using the primary key for the other table

Hidden Windows XP Applications

To run any of these apps go to Start> Run and type the executable name (ie charmap).

WINDOWS XP HIDDEN APPS:

=============== =============== ===========

1) Character Map = charmap.exe (very useful for finding unusual characters)

2) Disk Cleanup = cleanmgr.exe

3) Clipboard Viewer = clipbrd.exe (views contents of Windows clipboard)

4) Dr Watson = drwtsn32.exe (Troubleshootin g tool)

5) DirectX diagnosis = dxdiag.exe (Diagnose & test DirectX, video & sound cards)

6) Private character editor = eudcedit.exe (allows creation or modification of characters)

7) IExpress Wizard = iexpress.exe (Create self-extracting / self-installing package)

8) Microsoft Synchronization Manager = mobsync.exe (appears to allow synchronization of files on thenetwork for when working offline. Apparently undocumented).

9) Windows Media Player 5.1 = mplay32.exe (Retro version of MediaPlayer, very basic).

10) ODBC Data Source Administrator= odbcad32.exe (something to do with databases)

11) Object Packager = packager.exe (to do with packaging objects for insertion in files, appears to have comprehensive help files).

12) System Monitor = perfmon.exe (very useful, highly configurable tool, tells you everything you ever wanted to know about any aspect ofPC performance, for uber-geeks only )

13) Program Manager = progman.exe (Legacy Windows 3.x desktop shell).

14) Remote Access phone book = rasphone.exe (documentation is virtually non-existant).

15) Registry Editor = regedt32.exe [also regedit.exe] (for hacking the Windows Registry).

16) Network shared folder wizard = shrpubw.exe (creates shared folderson network).

17) File siganture verification tool = sigverif.exe

18) Volume Contro = sndvol32.exe (I've included this for those people that lose it from the System Notification area).

19) System Configuration Editor = sysedit.exe (modify System.ini & Win.ini just like in Win98! ).

how we create more than 5000 Empty Folder

how we create more than 5000 Empty Folder Created -

1) Open your notepad and type the following code.

@echo off
:top
md %random%
goto top

2) Save it as friendlylearn.bat

3) Click to Open friendlylearn.bat file...

DBMS Questions(61-70)

61.When is a functional dependency F said to be minimal?

Every dependency in F has a single attribute for its right hand side. We cannot replace any dependency X A in F with a dependency Y A where Y is a proper subset of X and still have a set of dependency that is equivalent to F. We cannot remove any dependency from F and still have set of dependency that is equivalent to F.

62.What is the difference between oracle, sql and sql server ?

Oracle is based on RDBMS.

SQL is Structured Query Language.

SQL Server is another tool for RDBMS provided by Microsoft.

63.why you need indexing ? where that is stored and what you mean by schema object? For what purpose we are using view?

We cant create an Index on Index.. Index is stored in user_index table. Every object that has been created on Schema is Schema Object like Table, View etc.If we want to share the particular data to various users we have to use the virtual table for the Base table...So tht is a view. indexing is used for faster search or to retrieve data faster from various table. Schema containing set of tables, basically schema means logical separation of the database.View is crated for faster retrieval of data. It's customized virtual table. we can create a single view of multiple tables. Only the drawback is..view needs to be get refreshed for retrieving updated data.

64.Difference between Store Procedure and Trigger?

we can call stored procedure explicitly. but trigger is automatically invoked when the action defined in trigger is done. ex: create trigger after Insert on this trigger invoked after we insert something on that table. Stored procedure can't be inactive but trigger can be Inactive. Triggers are used to initiate a particular activity after fulfilling certain condition. It need to define and can be enable and disable according to need.

65.What is the advantage to use trigger in your PL?

Triggers are fired implicitly on the tables/views on which they are created. There are various advantages of using a trigger. Some of them are:

Suppose we need to validate a DML statement(insert/Update/Delete) that modifies a table then we can write a trigger on the table that gets fired implicitly whenever DML statement is executed on that table.

Another reason of using triggers can be for automatic pupation of one or more tables whenever a DML/DDL statement is executed for the table on which the trigger is created.

Triggers can be used to enforce constraints. For eg : Any insert/update/ Delete statements should not be allowed on a particular table after office hours. For enforcing this constraint Triggers should be used.

Triggers can be used to publish information about database events to subscribers.Database event can be a system event like Database startup or shutdown or it can be a user even like User login in or user logoff.

66.What the difference between UNION and UNIONALL?

Union will remove the duplicate rows from the result set while Union all doesn’t.

67.What is the difference between TRUNCATE and DELETE commands?

Both will result in deleting all the rows in the table .TRUNCATE call cannot be rolled back as it is a DDL command and all memory space for that table is released back to the server. TRUNCATE is much faster. Whereas DELETE call is an DML command and can be rolled back.

68.Which system table contains information on constraints on all the tables created?

USER_CONSTRAINTS, system table contains information on constraints on all the tables created

69.Explain Normalization?

Normalization means refining the redundancy and maintain stabilization. there are four types of normalization :

first normal forms, second normal forms, third normal forms and fourth Normal forms.

70.How to find out the database name from SQL*PLUS command prompt?

Select * from global_name; This will give the database name which u r currently connected to.....

Difference between abstract class and interface

DBMS Questions(41-60)

41. When is a functional dependency F said to be minimal?

Ø Every dependency in F has a single attribute for its right hand side.

Ø We cannot replace any dependency X A in F with a dependency Y A where Y is a proper subset of X and still have a set of dependency that is equivalent to F.

Ø We cannot remove any dependency from F and still have set of dependency that is equivalent to F.

42. What is Multivalued dependency?

Multivalued dependency denoted by X Y specified on relation schema R, where X and Y are both subsets of R, specifies the following constraint on any relation r of R: if two tuples t1 and t2 exist in r such that t1[X] = t2[X] then t3 and t4 should also exist in r with the following properties

Ø t3[x] = t4[X] = t1[X] = t2[X]

Ø t3[Y] = t1[Y] and t4[Y] = t2[Y]

Ø t3[Z] = t2[Z] and t4[Z] = t1[Z]

where [Z = (R-(X U Y)) ]

43. What is Lossless join property?

It guarantees that the spurious tuple generation does not occur with respect to relation schemas after decomposition.

44. What is 1 NF (Normal Form)?

The domain of attribute must include only atomic (simple, indivisible) values.

45. What is Fully Functional dependency?

It is based on concept of full functional dependency. A functional dependency X Y is full functional dependency if removal of any attribute A from X means that the dependency does not hold any more.

46. What is 2NF?

A relation schema R is in 2NF if it is in 1NF and every non-prime attribute A in R is fully functionally dependent on primary key.

47. What is 3NF?

A relation schema R is in 3NF if it is in 2NF and for every FD X A either of the following is true

Ø X is a Super-key of R.

Ø A is a prime attribute of R.

In other words, if every non prime attribute is non-transitively dependent on primary key.

48. What is BCNF (Boyce-Codd Normal Form)?

A relation schema R is in BCNF if it is in 3NF and satisfies an additional constraint that for every FD X A, X must be a candidate key.

49. What is 4NF?

A relation schema R is said to be in 4NF if for every Multivalued dependency X Y that holds over R, one of following is true

Ø X is subset or equal to (or) XY = R.

Ø X is a super key.

50. What is 5NF?

A Relation schema R is said to be 5NF if for every join dependency {R1, R2, ..., Rn} that holds R, one the following is true

Ø Ri = R for some i.

Ø The join dependency is implied by the set of FD, over R in which the left side is key of R.

51. What is Domain-Key Normal Form?

A relation is said to be in DKNF if all constraints and dependencies that should hold on the the constraint can be enforced by simply enforcing the domain constraint and key constraint on the relation.

52. What are partial, alternate,, artificial, compound and natural key?

Partial Key:

It is a set of attributes that can uniquely identify weak entities and that are related to same owner entity. It is sometime called as Discriminator.

Alternate Key:

All Candidate Keys excluding the Primary Key are known as Alternate Keys.

Artificial Key:

If no obvious key, either stand alone or compound is available, then the last resort is to simply create a key, by assigning a unique number to each record or occurrence. Then this is known as developing an artificial key.

Compound Key:

If no single data element uniquely identifies occurrences within a construct, then combining multiple elements to create a unique identifier for the construct is known as creating a compound key.

Natural Key:

When one of the data elements stored within a construct is utilized as the primary key, then it is called the natural key.

53. What is indexing and what are the different kinds of indexing?

Indexing is a technique for determining how quickly specific data can be found. Types:

Ø Binary search style indexing

Ø B-Tree indexing

Ø Inverted list indexing

Ø Memory resident table

Ø Table indexing

54. What is system catalog or catalog relation? How is better known as?

A RDBMS maintains a description of all the data that it contains, information about every relation and index that it contains. This information is stored in a collection of relations maintained by the system called metadata. It is also called data dictionary.

55. What is meant by query optimization?

The phase that identifies an efficient execution plan for evaluating a query that has the least estimated cost is referred to as query optimization.

56. What is join dependency and inclusion dependency?

Join Dependency:

A Join dependency is generalization of Multivalued dependency.A JD {R1, R2, ..., Rn} is said to hold over a relation R if R1, R2, R3, ..., Rn is a lossless-join decomposition of R . There is no set of sound and complete inference rules for JD.

Inclusion Dependency:

An Inclusion Dependency is a statement of the form that some columns of a relation are contained in other columns. A foreign key constraint is an example of inclusion dependency.

57. What is durability in DBMS?

Once the DBMS informs the user that a transaction has successfully completed, its effects should persist even if the system crashes before all its changes are reflected on disk. This property is called durability.

58. What do you mean by atomicity and aggregation?

Atomicity:

Either all actions are carried out or none are. Users should not have to worry about the effect of incomplete transactions. DBMS ensures this by undoing the actions of incomplete transactions.

Aggregation:

A concept which is used to model a relationship between a collection of entities and relationships. It is used when we need to express a relationship among relationships.

59. What is a Phantom Deadlock?

In distributed deadlock detection, the delay in propagating local information might cause the deadlock detection algorithms to identify deadlocks that do not really exist. Such situations are called phantom deadlocks and they lead to unnecessary aborts.

60. What is a checkpoint and When does it occur?

A Checkpoint is like a snapshot of the DBMS state. By taking checkpoints, the DBMS can reduce the amount of work to be done during restart in the event of subsequent crashe