In the world of comic books, every bad guy is an evil genius. On the Web, hackers, spammers, and phishers may be evil, but they're not required to be geniuses. They can make a healthy living just by exploiting known security holes that many users haven't bothered to patch. Or by relying on the propensity of millions of people to do things they've been told over and over not to do.
The silver lining is that you don't have to be a genius to avoid these common attacks either. Implement a few simple fixes, and you'll avoid most of the bad stuff out there.
Fix 1: Patch Over the Software Bull's-Eye
Have you turned off automatic updates for Windows and other programs on the rationale that "if it ain't broke, don't fix it?" Then consider this: Your programs may be very, very broken, and you don't know it. The days of big splashy viruses that announce themselves to PC users are over. The modern cybercriminal prefers to invisibly take control of your PC, and unpatched software gives them the perfect opportunity to do so.
Today, a hijacked Web page--modern digital crooks' attack of choice--will launch a bevy of probes against your PC in search of just one unpatched vulnerability that a probe can exploit. If it finds one, better hope your antivirus program catches the ensuing attack. Otherwise you likely won't even notice anything amiss as it infects your system.
Luckily, you can completely block the majority of Web-based exploits by keeping all your programs--not just the operating system or your browsers--up-to-date. Attack sites ferret out holes in seemingly innocuous applications such as QuickTime and WinZip as well as in Windows and Internet Explorer. So turn on automatic update features for any software that offers the service--it's your quickest and easiest option for getting patches.
Fix 2: Find the Other Holes
If every program used easy automatic updates--and we were all smart enough to use them--the thriving malware business would take a serious hit. Until then, a free and easy security app from Secunia can help save the day.
The Secunia Personal Software Inspector, available as a free download, scans your installed software to let you know which out-of-date programs might be making your PC unsafe. But it doesn't stop there--for each old program it finds, it offers quick and easy action buttons such as one labeled Download Solution, which retrieves the latest software patch without you even having to open a browser.
The program also gives you links to the software vendor's site as well as Secunia's full report about the vulnerability on your system. You can choose to block future warnings about a particular program (but you should, of course, be careful before doing so).
Secunia PSI isn't perfect, and doesn't always make it easy to update unsafe program components. But for most apps it provides a quick--and very important--fix.
Fix 3: Let the Latest Browsers Fight for You
The most insidious hijacked Web pages are nearly impossible to spot. Tiny snippets of inserted code that don't display on the page can nevertheless launch devastating behind-the-scenes attacks.
Trying to avoid such pages on your own is asking for trouble, especially since crooks like to hack popular sites--attacks against sites for Sony games and the Miami Dolphins are just two well-known examples. But new site-blocking features in the just-released Firefox 3 and Opera 9.5 browsers provide some shielding.
Both browsers expand on the previous version's antiphishing features to block known malware sites as well, whether they're hijacked pages on legitimate sites or sites that were specifically created by bad guys. Neither browser completely eliminates the risk of landing on such pages, but every additional layer of protection helps.
Microsoft plans to add a similar feature to Internet Explorer 8, but this version won't be ready for prime time for a good while. For more on the browsers' improved security, see "New Browsers Fight the Malware Scourge."
Fix 4: Sidestep Social Engineering
The most dangerous crooks use clever marketing to get you to do their dirty work for them and infect your own PC. Lots of social engineering attacks are laughably crude, with misspelled words and clumsy grammar, but that doesn't mean you should dismiss the danger. Every now and then, a well-crafted attack can slip past your defenses and lure you into opening a poisonous e-mail attachment or downloaded file. A targeted attack might even use your correct name and business title.
To fight back, turn to a simple but powerful tool:Â VirusTotal.com. You can easily upload any file (up to 10MB) to the site and have it scanned by a whopping 35 different antivirus engines, including ones from Kaspersky, McAfee, and Symantec. A report tells you what each engine thought about your file. While some (such as Prevx) are prone to false alerts, if you get multiple specific warnings that include the name of the particular threat, then you almost certainly want to delete the file.
A lack of warnings doesn't guarantee a file is safe, but it does give you pretty good odds. Use VirusTotal to check every e-mail attachment and download you're not 100 percent sure about, and you'll avoid insidious social engineering.
If using VirusTotal starts to become a habit (not a bad idea) and you want to make sending files for scanning to VirusTotal really easy, download the free VirusTotal Uploader. Once you've installed the utility, just right-click a file, and you'll see an option (under Send To) to upload it to the VirusTotal site.
Fix 5: Get the Jump on Fast-Moving Malware
Traditional, signature-based antivirus software is getting snowed under by a blizzard of malware. Attackers try to evade detection by churning out more variants than security labs can analyze. So besides signatures, any antivirus program worth its salt today uses proactive detection that doesn't require a full signature to spot sneaky malware.
One promising approach uses behavioral analysis to identify malicious software based solely on how it acts on your PC. But your antivirus software by itself may not be enough. ThreatFire, a popular free download from PC Tools, adds such a layer of behavior-based protection. In recent tests, it correctly identified 90 percent of malware based on its behavior alone.
PC World's ThreatFire review provides a thorough analysis of the program and a quick download link (as well as a warning about installing too many security programs on one PC). And for more on behavioral analysis and proactive virus detection, see "When a Signature Isn't Enough."
Note: If you use the AVG Free antivirus program, hold off on trying ThreatFire until PC Tools releases a new version. The current 3.5 version conflicts with AVG, but PC Tools says it's working on a fix.
Fix 6: Rescue Your Inbox From Spam
Spam filters are getting better, but some junk still makes it through even the best of them. Instead of resigning yourself to hitting delete for all those hot-stock and Viagra come-ons, try disposable e-mail addresses.
Such an address is something you create every time you encounter an online shopping site, forum, or other service that requires you to enter an e-mail address. If that address gets flooded with spam, you can terminate it. That's a better system than the alternative, creating a free Web mail account that you use only for purchases and Web signups. With a single separate account, you have to throw the baby out with the bathwater and cancel the whole account if it gets too much spam.
Yahoo Web mail users can opt for the $20-a-year Plus service, which includes the AddressGuard disposable e-mail service (among other benefits). With it, you can click a bookmark to create a new, disposable address for any given site in about 10 seconds.
Gmail users can simply append "+ whatever" to their regular e-mail address before handing it out, but if that address starts to receive spam you can't simply turn it off. You'll have to create a filter in Gmail to block all mail to that address.
For everyone else, we suggest a good, free service from Spamgourmet.com that's quick and easy to set up and use; it allows you to create disposable addresses on-the-fly that will forward e-mail messages to your regular address.
Fix 7: Develop an Antiphishing Habit
The dastardly practice of phishing for personal information is still alive and well, and many fake sites can be hard to distinguish from the real ones. But a few simple practices can ensure you'll never be snagged by a phishing hook.
The best approach, and the most straightforward, is never to click a link in any e-mail message to access your financial accounts. Instead, always type the URL or use a bookmark. That one habit will protect you from almost every phishing attack.
If you can't make that change, then at least use the latest version of Internet Explorer, Firefox, or Opera to browse the Web. All have built-in features to block known phishing sites (and, as described in Fix 3, Opera and Firefox now also block known malware sites). Avoid Safari, which lacks any built-in antiphishing protection.
Finally, keep an eye out for the common phishing tactic of using URLs like "http://adwords.google.com.d0l9i.cn/select/Login." If you glance at the URL (an actual recent example listed by Phishtank.com), you might think the site's domain was google.com. In fact, it's heading to d0l9i.cn, a site in China where operators are standing by to swipe your personal details.
Internet Explorer 8 will use an innovative feature called Domain Highlighting that will make spotting such trickery easy. But until it becomes available, watch URLs carefully.
Fix 8: Keep Your Own Site Safe
It's not a good time to run a Web site. The Web may look like a digital wonderland, but behind the scenes it's a war zone. And the guns are trained on your site.
Crooks use automated tools to search sites for the most common vulnerabilities. If they find one, they blow the hole wide open to plant harmful code that will attack your loyal visitors.
To help keep your site safe, start with some quick, free scans that ferret out the most obvious problems. First, fill out a form at Qualys.com to request a free scan of one IP address.
Next, download the also-free Scrawlr tool from HP. After a quick install, use Scrawlr to scan your site for SQL injection vulnerabilities (a type of hole targeted in a recent Sony site hack).
A clean bill of health from both scans won't guarantee that your site is safe. For instance, neither will find problems with custom JavaScript code, another common type of attack. And while requesting or running either scan is easy, fixing a reported hole might involve a fair bit of work. But that job will still take far less work than repairing your site and your reputation after your site has been hijacked.
Fix 9: Make Your Passwords Secure--And Easy to Remember
Online passwords are starting to seem about as safe as tissue paper protecting a bank vault. The supply of stolen logins is now so huge that crooks can hardly make any money selling them unless they add other ripped-off data, like addresses or Social Security numbers, according to security researchers. And thieves don't stop with stealing logins to financial accounts--the bad guys regularly pilfer access information for Web mail accounts as well. In one recent case, a scammer broke into Web mail accounts and sent messages to the victim's friends asking for money.
Experts say we should use strong, unique passwords for all our accounts. But they don't tell us how we're supposed to remember them, so most of us end up using the same, not-so-safe password at all our accounts.
Here's an easy fix that allows you to remember just one password, yet still have a strong, unique password for each site you use. The Password Hash (or PwdHash) add-on for Firefox and IE takes that simple password you type and runs it through an algorithm that uses the site's domain name as part of the calculation. The utility subs in the resulting strong password before you send it to the site. All you have to do (after installing Password Hash) is hit the F2 key in a password box before you type.
Fix 10: Get Extra Cleaning Help for Stubborn Infections
Sometimes even the best antivirus program misses an infection. And once a virus or Trojan horse gets in, removing it can be incredibly tough. If you suspect some nasty got past your defenses, then it's time to bring in extra help.
Many antivirus makers offer free and easy online scans through your Web browser. The scan will take time, as the scanning service will need to download large Java or ActiveX components before it can get started, but they're easy to kick off. You can run them in addition to your already-installed antivirus application for a second (or third, or fourth) opinion. Here's the lowdown on your options.
- Trend Micro HouseCall: Will detect and remove malware; works with both IE and Firefox.
- BitDefender Online Scanner: Detects and removes malware; requires IE.
- Kaspersky Online Scanner: Detects malware, but doesn't remove it; works with IE and Firefox.
- F-Secure Online Virus Scanner: Detects and removes malware; requires IE.
- ESET Online Scanner: Detects and removes malware; requires IE.
Sunday, August 15, 2010
Sunday, March 14, 2010
Learn DBMS, Part - IV
KEY IN DBMS
The key is defined as the column or attribute of the database table. For example if a table has id,name and address as the column names then each one is known as the key for that table. We can also say that the table has 3 keys as id, name and address. The keys are also used to identify each record in the database table.The following are the various types of keys available in the DBMS system.
1. A simple key contains a single attribute.
2. A composite key is a key that contains more than one attribute.
3. A candidate key is an attribute (or set of attributes) that uniquely identifies a row. A candidate key must possess the following properties:
o Unique identification - For every row the value of the key must uniquely identify that row.
o Non redundancy - No attribute in the key can be discarded without destroying the property of unique identification.
4. A primary key is the candidate key which is selected as the principal unique identifier. Every relation must contain a primary key. The primary key is usually the key selected to identify a row when the database is physically implemented. For example, a part number is selected instead of a part description.
5. A superkey is any set of attributes that uniquely identifies a row. A superkey differs from a candidate key in that it does not require the non redundancy property.
6. A foreign key is an attribute (or set of attributes) that appears (usually) as a non key attribute in one relation and as a primary key attribute in another relation. I say usually because it is possible for a foreign key to also be the whole or part of a primary key:
o A many-to-many relationship can only be implemented by introducing an intersection or link table which then becomes the child in two one-to-many relationships. The intersection table therefore has a foreign key for each of its parents, and its primary key is a composite of both foreign keys.
o A one-to-one relationship requires that the child table has no more than one occurrence for each parent, which can only be enforced by letting the foreign key also serve as the primary key.
7. A semantic or natural key is a key for which the possible values have an obvious meaning to the user or the data. For example, a semantic primary key for a COUNTRY entity might contain the value 'USA' for the occurrence describing the United States of America. The value 'USA' has meaning to the user.
8. A technical or surrogate or artificial key is a key for which the possible values have no obvious meaning to the user or the data. These are used instead of semantic keys for any of the following reasons:
o When the value in a semantic key is likely to be changed by the user, or can have duplicates. For example, on a PERSON table it is unwise to use PERSON_NAME as the key as it is possible to have more than one person with the same name, or the name may change such as through marriage.
o When none of the existing attributes can be used to guarantee uniqueness. In this case adding an attribute whose value is generated by the system, e.g. from a sequence of numbers, is the only way to provide a unique value. Typical examples would be ORDER_ID and INVOICE_ID. The value '12345' has no meaning to the user as it conveys nothing about the entity to which it relates.
NORMALIZATION
Data normalization is a set of rules and techniques concerned with:
• Identifying relationships among attributes.
• Combining attributes to form relations.
• Combining relations to form a database.
It follows a set of rules worked out by E FCodd in 1970. A normalized relational database provides several benefits:
• Elimination of redundant data storage.
• Close modeling of real world entities, processes, and their relationships.
• Structuring of data so that the model is flexible.
Because the principles of normalization were first written using the same terminology as was used to define the relational data model this led some people to think that normalization is difficult. Nothing could be more untrue. The principles of normalization are simple, common sense ideas that are easy to apply.
The only attribute values permitted by 1 NF are single atomic (or indivisible) values. If there is no value present for the column, then it should be denoted as null.
BCNF
A table is in Boyce-Codd normal form (BCNF) if and only if it is in 3NF and every determinant is a candidate key.
1. Anomalies can occur in relations in 3NF if there is a composite key in which part of that key has a determinant which is not itself a candidate key.
2. This can be expressed as R(A,B,C), C--->A where:
o The relation R contains attributes A, B and C.
o A and B form a candidate key.
o C is the determinant for A (A is functionally dependent on C).
o C is not part of any key.
3. Anomalies can also occur where a relation contains several candidate keys where:
o The keys contain more than one attribute (they are composite keys).
o An attribute is common to more than one key.
The key is defined as the column or attribute of the database table. For example if a table has id,name and address as the column names then each one is known as the key for that table. We can also say that the table has 3 keys as id, name and address. The keys are also used to identify each record in the database table.The following are the various types of keys available in the DBMS system.
1. A simple key contains a single attribute.
2. A composite key is a key that contains more than one attribute.
3. A candidate key is an attribute (or set of attributes) that uniquely identifies a row. A candidate key must possess the following properties:
o Unique identification - For every row the value of the key must uniquely identify that row.
o Non redundancy - No attribute in the key can be discarded without destroying the property of unique identification.
4. A primary key is the candidate key which is selected as the principal unique identifier. Every relation must contain a primary key. The primary key is usually the key selected to identify a row when the database is physically implemented. For example, a part number is selected instead of a part description.
5. A superkey is any set of attributes that uniquely identifies a row. A superkey differs from a candidate key in that it does not require the non redundancy property.
6. A foreign key is an attribute (or set of attributes) that appears (usually) as a non key attribute in one relation and as a primary key attribute in another relation. I say usually because it is possible for a foreign key to also be the whole or part of a primary key:
o A many-to-many relationship can only be implemented by introducing an intersection or link table which then becomes the child in two one-to-many relationships. The intersection table therefore has a foreign key for each of its parents, and its primary key is a composite of both foreign keys.
o A one-to-one relationship requires that the child table has no more than one occurrence for each parent, which can only be enforced by letting the foreign key also serve as the primary key.
7. A semantic or natural key is a key for which the possible values have an obvious meaning to the user or the data. For example, a semantic primary key for a COUNTRY entity might contain the value 'USA' for the occurrence describing the United States of America. The value 'USA' has meaning to the user.
8. A technical or surrogate or artificial key is a key for which the possible values have no obvious meaning to the user or the data. These are used instead of semantic keys for any of the following reasons:
o When the value in a semantic key is likely to be changed by the user, or can have duplicates. For example, on a PERSON table it is unwise to use PERSON_NAME as the key as it is possible to have more than one person with the same name, or the name may change such as through marriage.
o When none of the existing attributes can be used to guarantee uniqueness. In this case adding an attribute whose value is generated by the system, e.g. from a sequence of numbers, is the only way to provide a unique value. Typical examples would be ORDER_ID and INVOICE_ID. The value '12345' has no meaning to the user as it conveys nothing about the entity to which it relates.
NORMALIZATION
Data normalization is a set of rules and techniques concerned with:
• Identifying relationships among attributes.
• Combining attributes to form relations.
• Combining relations to form a database.
It follows a set of rules worked out by E FCodd in 1970. A normalized relational database provides several benefits:
• Elimination of redundant data storage.
• Close modeling of real world entities, processes, and their relationships.
• Structuring of data so that the model is flexible.
Because the principles of normalization were first written using the same terminology as was used to define the relational data model this led some people to think that normalization is difficult. Nothing could be more untrue. The principles of normalization are simple, common sense ideas that are easy to apply.
The only attribute values permitted by 1 NF are single atomic (or indivisible) values. If there is no value present for the column, then it should be denoted as null.
BCNF
A table is in Boyce-Codd normal form (BCNF) if and only if it is in 3NF and every determinant is a candidate key.
1. Anomalies can occur in relations in 3NF if there is a composite key in which part of that key has a determinant which is not itself a candidate key.
2. This can be expressed as R(A,B,C), C--->A where:
o The relation R contains attributes A, B and C.
o A and B form a candidate key.
o C is the determinant for A (A is functionally dependent on C).
o C is not part of any key.
3. Anomalies can also occur where a relation contains several candidate keys where:
o The keys contain more than one attribute (they are composite keys).
o An attribute is common to more than one key.
Saturday, March 13, 2010
Learn DBMS, Part III
DATABASE SYSTEM ARCHITECT
Following are the three types of database architectures:
1. Client-Server Database Systems
A client is defined as a requester of services and a server is defined as the provider of services.
Today centralized systems act as server systems that satisfy requests generated by client systems.
Functionally database systems can be broadly divided into two parts:
• Front end: front end of a database system consists of tools such as SQL user interface, forms interfaces, reports generation tools, and analysis tools.
• Back end: The back end of a database system manages query evaluation and optimization, access structures, concurrency control and recovery management.
2. Parallel Systems
In parallel processing, many operations are performed simultaneously and the computational steps are performed sequentially. It can process thousands of transactions per second.
There are four types of Architectural Models for Parallel Processing:
• Shared Memory (tightly coupled) architecture: Multiple processors share secondary (disk) storage and also share primary memory.
• Shared Disk (loosely coupled) architecture: Multiple processors share secondary (disk) storage but each has their own primary memory.
• Shared Nothing: The processors share neither a common memory nor common disk.
• Hierarchical: this model is the combination of preceding three architectures.
3. Distributed Systems
Distributed database is a collection of multiple logically interrelated databases distributed over a computer network and a distributed database management system is a software system that manages a distributed database while making the distribution transparent to the user. Transparency means hiding the details of where the data is physically stored within the system.
Reasons for building a distributed database are sharing of data, autonomy, and availability.
Functions of distributed databases:
• Keeping track of data.
• Query Processing by a communication network.
• Security Management.
• Distributed Transaction Management
• Database Recovery.
CODD’S RULE
E.F. Codd, the famous mathematician has introduce 12 rules for the relational model for databases commonly known as Codd's rules. The rules mainly define what is required for a DBMS for it to be considered relational , i.e., an RDBMS. There is also one more rule i.e Rule00 which specifies the relational model should use the relational way to manage the database. The rules and their description is as follows:-
Rule 000: A RDBMS system should be capable of using its relational facilities (exclusively) to manage the database.
Rule 1: The information rule : All information in the database is to be represented in one and only one way. This is achieved by values in column positions within rows of tables.
Rule 2 : The guaranteed access rule : All data must be accessible with no ambiguity.This is achieved in the RDBMS by using the primary key concept.
Rule 3: Systematic treatment of null values : The DBMS must allow each field to remain null. The null can be stored in any field of any datatype.
Rule 4: Active online catalog based on the relational model : The authorized users can access the database structure by using common language i.e SQL.
Rule 5: The comprehensive data sublanguage rule : The system must support at least one relational language that has simple syntax and transaction management facilities. It can be used in the application as well as in the RDBMS systems.
Rule 6: The view updating rule : All views must be updatable by the system.
Rule 7: High-level insert, update, and delete : The system is able to insert, update and delete operations fully. It can also perform the operations on multiple rows simultenously.
Rule 8: Physical data independence : Changes to the physical storage structure must not require a change to an application based on the structure.
Rule 9: Logical data independence : Changes to the logical level (tables, columns, rows, and so on) must not require a change to an application based on the structure.
Rule 10: Integrity independence : All the Integrity constraints like primary key, uniques key etc must be specified separately from application programs and stored in the catalog.
Rule 11: Distribution independence : The distribution of portions of the database to various locations should be invisible to users of the database.
Rule 12: The nonsubversion rule : If the system provides a low-level (record-at-a-time) interface, then that interface cannot be used to subvert the system, for example, bypassing a relational security or integrity constraint.
Note:- Any database management system which fulfills 6 or more than 6 rules can be considered as the RDBMS.
Following are the three types of database architectures:
1. Client-Server Database Systems
A client is defined as a requester of services and a server is defined as the provider of services.
Today centralized systems act as server systems that satisfy requests generated by client systems.
Functionally database systems can be broadly divided into two parts:
• Front end: front end of a database system consists of tools such as SQL user interface, forms interfaces, reports generation tools, and analysis tools.
• Back end: The back end of a database system manages query evaluation and optimization, access structures, concurrency control and recovery management.
2. Parallel Systems
In parallel processing, many operations are performed simultaneously and the computational steps are performed sequentially. It can process thousands of transactions per second.
There are four types of Architectural Models for Parallel Processing:
• Shared Memory (tightly coupled) architecture: Multiple processors share secondary (disk) storage and also share primary memory.
• Shared Disk (loosely coupled) architecture: Multiple processors share secondary (disk) storage but each has their own primary memory.
• Shared Nothing: The processors share neither a common memory nor common disk.
• Hierarchical: this model is the combination of preceding three architectures.
3. Distributed Systems
Distributed database is a collection of multiple logically interrelated databases distributed over a computer network and a distributed database management system is a software system that manages a distributed database while making the distribution transparent to the user. Transparency means hiding the details of where the data is physically stored within the system.
Reasons for building a distributed database are sharing of data, autonomy, and availability.
Functions of distributed databases:
• Keeping track of data.
• Query Processing by a communication network.
• Security Management.
• Distributed Transaction Management
• Database Recovery.
CODD’S RULE
E.F. Codd, the famous mathematician has introduce 12 rules for the relational model for databases commonly known as Codd's rules. The rules mainly define what is required for a DBMS for it to be considered relational , i.e., an RDBMS. There is also one more rule i.e Rule00 which specifies the relational model should use the relational way to manage the database. The rules and their description is as follows:-
Rule 000: A RDBMS system should be capable of using its relational facilities (exclusively) to manage the database.
Rule 1: The information rule : All information in the database is to be represented in one and only one way. This is achieved by values in column positions within rows of tables.
Rule 2 : The guaranteed access rule : All data must be accessible with no ambiguity.This is achieved in the RDBMS by using the primary key concept.
Rule 3: Systematic treatment of null values : The DBMS must allow each field to remain null. The null can be stored in any field of any datatype.
Rule 4: Active online catalog based on the relational model : The authorized users can access the database structure by using common language i.e SQL.
Rule 5: The comprehensive data sublanguage rule : The system must support at least one relational language that has simple syntax and transaction management facilities. It can be used in the application as well as in the RDBMS systems.
Rule 6: The view updating rule : All views must be updatable by the system.
Rule 7: High-level insert, update, and delete : The system is able to insert, update and delete operations fully. It can also perform the operations on multiple rows simultenously.
Rule 8: Physical data independence : Changes to the physical storage structure must not require a change to an application based on the structure.
Rule 9: Logical data independence : Changes to the logical level (tables, columns, rows, and so on) must not require a change to an application based on the structure.
Rule 10: Integrity independence : All the Integrity constraints like primary key, uniques key etc must be specified separately from application programs and stored in the catalog.
Rule 11: Distribution independence : The distribution of portions of the database to various locations should be invisible to users of the database.
Rule 12: The nonsubversion rule : If the system provides a low-level (record-at-a-time) interface, then that interface cannot be used to subvert the system, for example, bypassing a relational security or integrity constraint.
Note:- Any database management system which fulfills 6 or more than 6 rules can be considered as the RDBMS.
Friday, March 12, 2010
Learn DBMS, Part - II
DATA MODELS:
Data model is defined as the collection of conceptual tools for describing data, data relationships, data semantics and consistency constraints. There are following four Data Model exists.
The Hierarchical Data Model
A hierarchical database consists of the following:
1. It contains nodes connected by branches same as the trees in datastructers.
2. The top node is called the root.
3. If multiple nodes appear at the top level, the nodes are called root segments.
4. The parent of node nx is a node directly above nx and connected to nx by a branch.
5. Each node (with the exception of the root) has exactly one parent.
6. The child of node nx is the node directly below nx and connected to nx by a branch.
7. One parent may have many children.
The Network Data Model
Like the The Hierarchical Data Model the Network Data Model also consists of nodes and branches, but a child may have multiple parents within the network structure.
The Relational Data Model
The Relational Data Model has the relation at its heart, but then a whole series of rules governing keys, relationships, joins, functional dependencies, transitive dependencies, multi-valued dependencies, and modification anomalies. A relation is subject to the following rules:
1. Relation (file, table) is a two-dimensional table.
2. Attribute (i.e. field or data item) is a column in the table.
3. Each column in the table has a unique name within that table.
4. Each column is homogeneous. Thus the entries in any column are all of the same type (e.g. age, name, employee-number, etc).
5. Each column has a domain, the set of possible values that can appear in that column.
6. A Tuple (i.e. record) is a row in the table.
7. The order of the rows and columns is not important.
8. Values of a row all relate to some thing or portion of a thing.
9. Repeating groups (collections of logically related attributes that occur multiple times within one record occurrence) are not allowed.
10. Duplicate rows are not allowed (candidate keys are designed to prevent this).
11. Cells must be single-valued (but can be variable length). Single valued means the following:
1. Cannot contain multiple values such as 'A1,B2,C3'.
2. Cannot contain combined values such as 'ABC-XYZ' where 'ABC' means one thing and 'XYZ' another.
Object Oriented Model
In object oriented model information is represented in the form of objects as used in object oriented programming. Object Oriented Database Management Systems is a combination of object oriented programming language capabilities and database capabilities. It contains some properties like transparently persisted data, concurrency control, data recovery, associative queries, and other capabilities. Some object oriented programming languages are Java, C++, .NET, Visual Basic, Python etc. Most object databases also offer some kind of query language, allowing objects to be found by a more declarative programming approach.
THREE SCHEMA ARCHITECTURE
The goal of Three-Schema architecture is to separate the user applications and physical database. In this architecture, schemas can be defined at the following three levels:
• The internal level:- The internal level has an internal schema which describes the physical storage structure of the database.
• The conceptual level:-The conceptual level has a conceptual schema, it describes the entities, data types, relationships, user operations, and constraints.
• The external level or view level:- The external or view level includes a number of external schemas or user views. It describes the part of the database that a particular user group is interested in and hides the rest of the database from that user group.
Data model is defined as the collection of conceptual tools for describing data, data relationships, data semantics and consistency constraints. There are following four Data Model exists.
The Hierarchical Data Model
A hierarchical database consists of the following:
1. It contains nodes connected by branches same as the trees in datastructers.
2. The top node is called the root.
3. If multiple nodes appear at the top level, the nodes are called root segments.
4. The parent of node nx is a node directly above nx and connected to nx by a branch.
5. Each node (with the exception of the root) has exactly one parent.
6. The child of node nx is the node directly below nx and connected to nx by a branch.
7. One parent may have many children.
The Network Data Model
Like the The Hierarchical Data Model the Network Data Model also consists of nodes and branches, but a child may have multiple parents within the network structure.
The Relational Data Model
The Relational Data Model has the relation at its heart, but then a whole series of rules governing keys, relationships, joins, functional dependencies, transitive dependencies, multi-valued dependencies, and modification anomalies. A relation is subject to the following rules:
1. Relation (file, table) is a two-dimensional table.
2. Attribute (i.e. field or data item) is a column in the table.
3. Each column in the table has a unique name within that table.
4. Each column is homogeneous. Thus the entries in any column are all of the same type (e.g. age, name, employee-number, etc).
5. Each column has a domain, the set of possible values that can appear in that column.
6. A Tuple (i.e. record) is a row in the table.
7. The order of the rows and columns is not important.
8. Values of a row all relate to some thing or portion of a thing.
9. Repeating groups (collections of logically related attributes that occur multiple times within one record occurrence) are not allowed.
10. Duplicate rows are not allowed (candidate keys are designed to prevent this).
11. Cells must be single-valued (but can be variable length). Single valued means the following:
1. Cannot contain multiple values such as 'A1,B2,C3'.
2. Cannot contain combined values such as 'ABC-XYZ' where 'ABC' means one thing and 'XYZ' another.
Object Oriented Model
In object oriented model information is represented in the form of objects as used in object oriented programming. Object Oriented Database Management Systems is a combination of object oriented programming language capabilities and database capabilities. It contains some properties like transparently persisted data, concurrency control, data recovery, associative queries, and other capabilities. Some object oriented programming languages are Java, C++, .NET, Visual Basic, Python etc. Most object databases also offer some kind of query language, allowing objects to be found by a more declarative programming approach.
THREE SCHEMA ARCHITECTURE
The goal of Three-Schema architecture is to separate the user applications and physical database. In this architecture, schemas can be defined at the following three levels:
• The internal level:- The internal level has an internal schema which describes the physical storage structure of the database.
• The conceptual level:-The conceptual level has a conceptual schema, it describes the entities, data types, relationships, user operations, and constraints.
• The external level or view level:- The external or view level includes a number of external schemas or user views. It describes the part of the database that a particular user group is interested in and hides the rest of the database from that user group.
Thursday, March 11, 2010
Learn DBMS
DBMS stands for Database Management System. A DBMS consists of collection of interrelated data and a set of program to access that data. The collection of data is known as a database. A database consists of the data relat ed to one organization. Prior to DBMS systems, the data was kept under the file system in forms of multiple files. The following are the disadvantages of the File system:-
1. Difficulty in Accessing data:- In the file system it is very difficult to find the data which is needed for some specific purpose. Like to get the average sale of the quarter needs to process all files for the quarter and then do some processing.
2. Data inconsistency and redundancy:- As the files and processing systems created by different vendors and programmers, so there is a inconsistency of data as different people prefer the different style of data handling. Also the different systems may use the different programming languages to develop the processing systems so the multiple copies of the same file kept under various places so redundancy is another problem we have with file system.
3. Security Problem:- There is a great risk of unauthroized person access the file system and get the data. So security is the major concern in the file system.
4. Integrity Problem:- The integrity issue is also a major concern as the data stored in the file can be changed easily. While creating files there is no specific rules checked while storing the data.
Advantages of Database Management System:-
The following are the advantages of DBMS systems:-
1. A data can be validated before storing into the DBMS system.These rules for data validation are known as Constraints in DBMS.
2. Different users can be created with different rights for the database.So DBMS systems are more secure than the conventional file system.
3. The relationships of the data can also be stored along with the data which is not possible for the files.
4. A simple english like language SQL is introduced which helps to access data more efficiently and quickly.
5. Multiple users can access the data simultenously and DBMS system will take care the conflicts.
6. The dependent tasks can be controlled with transaction management facility of the DBMS.
For example:- Transfering the cash from one account to second account consits of withdrawing the amount from one account and deposit in other. What if the application fails after the withdrawl so DBMS system will rollback the withdrawl automatically
1. Difficulty in Accessing data:- In the file system it is very difficult to find the data which is needed for some specific purpose. Like to get the average sale of the quarter needs to process all files for the quarter and then do some processing.
2. Data inconsistency and redundancy:- As the files and processing systems created by different vendors and programmers, so there is a inconsistency of data as different people prefer the different style of data handling. Also the different systems may use the different programming languages to develop the processing systems so the multiple copies of the same file kept under various places so redundancy is another problem we have with file system.
3. Security Problem:- There is a great risk of unauthroized person access the file system and get the data. So security is the major concern in the file system.
4. Integrity Problem:- The integrity issue is also a major concern as the data stored in the file can be changed easily. While creating files there is no specific rules checked while storing the data.
Advantages of Database Management System:-
The following are the advantages of DBMS systems:-
1. A data can be validated before storing into the DBMS system.These rules for data validation are known as Constraints in DBMS.
2. Different users can be created with different rights for the database.So DBMS systems are more secure than the conventional file system.
3. The relationships of the data can also be stored along with the data which is not possible for the files.
4. A simple english like language SQL is introduced which helps to access data more efficiently and quickly.
5. Multiple users can access the data simultenously and DBMS system will take care the conflicts.
6. The dependent tasks can be controlled with transaction management facility of the DBMS.
For example:- Transfering the cash from one account to second account consits of withdrawing the amount from one account and deposit in other. What if the application fails after the withdrawl so DBMS system will rollback the withdrawl automatically
How to Start a Conversation with New People
Start with a “hello,” and simply tell the new person your name then ask them theirs. Offer your hand to shake, upon his/her responding to you. (If you go to other countries, greet the person in tune with the particular culture). If you already know the person, skip this step and proceed to step.
Look around. See if there is anything worth pointing out. Sure, talking about the weather is a cliche, but if there’s something unusual about it–bam!–you’ve got a great topic of conversation.
Offer a compliment. Don’t lie and say you love someone’s hair when you think it’s revolting, but if you like his or her shoes, or a handbag, say so. A sincere compliment is a wonderful way to get someone to warm up to you. But be careful not to say something so personal that you scare the person off or make him or her feel uncomfortable. It is best not to compliment a person’s looks or body.
Ask questions! Most people love to talk about themselves — get them going. “What classes are you taking this year?” “Have you seen (Insert-Something- Here)? What did you think of it?” Again, keep the questions light and not invasive. Do not ask too many questions if he or she is not responsive to them.
Jump on any conversation- starters he or she might offer; take something he or she has said and run with it. Agree, disagree, ask a question about it, or offer an opinion, just don’t let it go by without notice.
Look your newfound friend in the eye, it engenders trust (but don’t stare). Also, use the person’s name a time or two during the conversation; it will help you remember the name, and will draw the person’s attention to what you are talking about.
Don’t forget to smile and have fun with your conversation!
Tips
Just relax. Chances are that whatever small-talk you’re making isn’t going to stick out in anyone’s mind a few months from now. Just say whatever comes into your head, so long as it’s not offensive or really weird. (Unless, of course, the person you’re attempting to converse with is into weird stuff.)
Remember, if you think of something in your head while you’re talking, it’s probably related.
It will help if you watch some TV, listen to radio shows, and/or read a lot — newspapers, magazines, and/or books. You need to have some idea of what is going on in the world. Also remember and plan to share anything you like, think is funny, or find intriguing. This is building up your own library of things that might be helpful to another person during a conversation someday. It will be amazing how you thread these interesting things when you least expect it, and make conversation an adventure instead of a dreadful task. If you take it to the next step and say things that you want the person to think of as adding value, and keep to yourself things that the person might not, you are actually honing your own personality to be appealing to the other person, and what is a greater act of kindness than that.
If you are shy, it will be helpful to have thought about a topic or two that you could talk about.
Follow the lead that your listener is expressing. If he or she appears interested, then continue. If he or she is looking at a clock or watch, or worse, looking for an escape strategy, then you have been going on for too long.
Interesting and funny quotes or facts can lighten things up, and make way for things to talk about. You could also use a set of conversation starter question cards for inspiration.
If talking over the phone, keep the person involved in the conversation at all costs. If you can’t come up with a good topic, try the “questions” game. Just keep asking them questions; random questions work just fine as long as they are appropriate. This technique can save a phone conversation. The questions should be open ended questions that do not require a yes or no answer. For example “How do you know the hosts?” This way you can ask questions about what they just said or follow up with how you know the hosts (for example) instead of acting as if the conversation is an interrogation.
Half of an effective conversation is the way you non-verbally communicate, and not necessarily what you say. Practice better non-verbal skills that are friendly and confident.
Read newspapers and magazines to increase your knowledge so you can have more interesting things to talk about.
Happy Talking..
Look around. See if there is anything worth pointing out. Sure, talking about the weather is a cliche, but if there’s something unusual about it–bam!–you’ve got a great topic of conversation.
Offer a compliment. Don’t lie and say you love someone’s hair when you think it’s revolting, but if you like his or her shoes, or a handbag, say so. A sincere compliment is a wonderful way to get someone to warm up to you. But be careful not to say something so personal that you scare the person off or make him or her feel uncomfortable. It is best not to compliment a person’s looks or body.
Ask questions! Most people love to talk about themselves — get them going. “What classes are you taking this year?” “Have you seen (Insert-Something- Here)? What did you think of it?” Again, keep the questions light and not invasive. Do not ask too many questions if he or she is not responsive to them.
Jump on any conversation- starters he or she might offer; take something he or she has said and run with it. Agree, disagree, ask a question about it, or offer an opinion, just don’t let it go by without notice.
Look your newfound friend in the eye, it engenders trust (but don’t stare). Also, use the person’s name a time or two during the conversation; it will help you remember the name, and will draw the person’s attention to what you are talking about.
Don’t forget to smile and have fun with your conversation!
Tips
Just relax. Chances are that whatever small-talk you’re making isn’t going to stick out in anyone’s mind a few months from now. Just say whatever comes into your head, so long as it’s not offensive or really weird. (Unless, of course, the person you’re attempting to converse with is into weird stuff.)
Remember, if you think of something in your head while you’re talking, it’s probably related.
It will help if you watch some TV, listen to radio shows, and/or read a lot — newspapers, magazines, and/or books. You need to have some idea of what is going on in the world. Also remember and plan to share anything you like, think is funny, or find intriguing. This is building up your own library of things that might be helpful to another person during a conversation someday. It will be amazing how you thread these interesting things when you least expect it, and make conversation an adventure instead of a dreadful task. If you take it to the next step and say things that you want the person to think of as adding value, and keep to yourself things that the person might not, you are actually honing your own personality to be appealing to the other person, and what is a greater act of kindness than that.
If you are shy, it will be helpful to have thought about a topic or two that you could talk about.
Follow the lead that your listener is expressing. If he or she appears interested, then continue. If he or she is looking at a clock or watch, or worse, looking for an escape strategy, then you have been going on for too long.
Interesting and funny quotes or facts can lighten things up, and make way for things to talk about. You could also use a set of conversation starter question cards for inspiration.
If talking over the phone, keep the person involved in the conversation at all costs. If you can’t come up with a good topic, try the “questions” game. Just keep asking them questions; random questions work just fine as long as they are appropriate. This technique can save a phone conversation. The questions should be open ended questions that do not require a yes or no answer. For example “How do you know the hosts?” This way you can ask questions about what they just said or follow up with how you know the hosts (for example) instead of acting as if the conversation is an interrogation.
Half of an effective conversation is the way you non-verbally communicate, and not necessarily what you say. Practice better non-verbal skills that are friendly and confident.
Read newspapers and magazines to increase your knowledge so you can have more interesting things to talk about.
Happy Talking..
Tuesday, January 26, 2010
WORDLESS WISDOM
"Every drop of tear is costly than anything in the world, but No One knows it's value until they have it in their own eyes for someone!"
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