by Dinesh Thakur Category: RDBMS

Relational operators are classified into two types:
• Traditional Set Operators
• Special Operators

 
by Dinesh Thakur Category: RDBMS

We have already seen relational algebra is a procedural language, in which user has to write the steps or procedure to obtain the required results but in general a user should not have to be concerned with the details of how to obtain information. In relational calculus user is not concerned with the procedure to obtain the results, he/she just tell his/her requirements and the output is available without knowing the method about its retrieval.



 
by Dinesh Thakur Category: RDBMS

Designing of database is most important responsibility of the software professionals who are dealing with the database related projects. For this they follow the Design Methodology. It helps the designer to plan, manage, control, and evaluate database development projects.



 
by Dinesh Thakur Category: RDBMS

A relation is said to be in First Normal Form (lNF) if and only if every entry of the relation (the intersection of a tuple and a column) has at most a single value. In other words "a relation is in First Normal Form if and only if all underlying domains contain atomic values or single value only."

 
by Dinesh Thakur Category: RDBMS

It deals with the cost of implementing locks depending upon the space and time. Here, space refers to data structure in DBMS for each lock and time refers to handling of lock request and release.
The cost of implementing locks depends on the size of data items. There are two types of lock granularity:



 
by Dinesh Thakur Category: RDBMS

A relation R is in Third Normal Form (3NF) if and only if the following conditions are satisfied simultaneously:
1. R is already in 2NF
2. No nonprime attribute is transitively dependent on the key.
Another way of expressing the conditions for Third Normal Form is as follows:
1. R is already in 2NF
2. No nonprime attribute functionally determines any other nonprime attribute.
These two sets of conditions are equivalent.

As these two definitions of 3NF imply, the objective of transforming relations into 3NF is to remove all transitive dependencies. So, first we are going to explain the concept of transitive dependency.

 
by Dinesh Thakur Category: RDBMS

In order to understand deadlock, let us consider the following example:

 

 
by Dinesh Thakur Category: RDBMS

Dr. E.F. Codd, the founder of the relational database systems, framed twelve rules to assist a database product to qualify as relational. An RDBMS product has to satisfy at least six of the 12 rules of Codd to be accepted as a full-fledged RDBMS. There is no RDBMS package commercially available that satisfies all the 12 rules. These rules are:



 
by Dinesh Thakur Category: RDBMS

There are two approaches used in algorithms to deals with the problems of concurrency control. These are:
• Pessimistic Approach
• Optimistic Approach

 
by Dinesh Thakur Category: RDBMS

Definition of second normal form is:

A relation R is in second normal form (2NF) if and only if it is in INF and very non-key attribute is fully dependent on the primary key.

 
by Dinesh Thakur Category: RDBMS

Denormalization is the process of attempting to optimize the performance of a database by adding redundant data or by grouping data. In some cases, denormalization helps cover up the inefficiencies inherent in relational database software. A relational normalized database imposes a heavy access load over physical storage of data even if it is well tuned for high performance.



 
by Dinesh Thakur Category: RDBMS

When a transaction requests a lock on a data item in a particular mode, and no other transaction has a lock on the same data item in a conflicting mode, the lock can be granted. However care must be taken to avoid the following scenario.

 
by Dinesh Thakur Category: Advanced Database Tech.

The distribution of data and applications has potential advantages over traditional centralized database systems. Unfortunately, there are also disadvantages; in this section we review the advantages and disadvantages of DDBMS.



 
by Dinesh Thakur Category: Advanced Database Tech.

Object Oriented Database (OODB) provides all the facilities associated with object oriented paradigm. It enables us to create classes, organize objects, structure an inheritance hierarchy and call methods of other classes. Besides these, it also provides the facilities associated with standard database systems. However, object oriented database systems have not yet replaced the RDBMS in commercial business applications.



 
by Dinesh Thakur Category: Advanced Database Tech.

Today, multinational companies and large organizations have operations in many places within their origin country and other parts of the world. Each place of operations may generate large volume of data. For example, insurance companies may have data from thousands of local and external branches large retail chains have data from hundreds or thousands of stores and so on. Corporate decision maker require access of information from all such sources.



 
by Dinesh Thakur Category: Advanced Database Tech.

A DDBMS may be classified as homogeneous or heterogeneous. In a homogeneous system, all sites use the same DBMS product. In a heterogeneous system, sites may run different DBMS products, which need not be based on the same underlying data model, and so the system may be composed of relational, network, hierarchical and object-oriented DBMSs.



 
by Dinesh Thakur Category: Advanced Database Tech.

Data can be stored in different computers by fragmenting the whole database into several pieces called fragments. Each piece is stored at a different site.

Fragments are logical data units stored at various sites in a distributed database system.



 
by Dinesh Thakur Category: Advanced Database Tech.

Data Replication is the process of storing data in more than one site or node. This is necessary for improving the availability of data. There can be full replication, in which a copy of the whole database is stored at every site. There can also be partial replication, in which case, some fragment (important frequently· used fragments) of the database are replicated and others are not replicated. There are a number of advantages and disadvantages to replication.



 
by Dinesh Thakur Category: Advanced Database Tech.

"A logically interrelated collection of shared data (and a description of this data) physically distributed over a computer network."



 
by Dinesh Thakur Category: Advanced Database Tech.

The definition of and DDBMS defines that the system should make the distribution transparent to the user. Transparent hides implementation details from the user. For example, in a centralized DBMS, data independence is a form of transparency it hides changes in the definition and organization of the data from the user. A DDBMS may provide a various· levels of transparency. However, they all participate in the same overall objective: to make the use of the distributed database, equivalent to that of a centralized database.



 

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About Dinesh Thakur

Dinesh ThakurDinesh Thakur holds an B.SC (Computer Science), MCSE, MCDBA, CCNA, CCNP, A+, SCJP certifications. Dinesh authors the hugely popular blog. Where he writes how-to guides around Computer fundamental , computer software, Computer programming, and web apps. For any type of query or something that you think is missing, please feel free to Contact us.